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Marijuana Leaf Symptoms and Nutrient Deficiencies – Sick Plants

Cannabis – Symptoms and Deficiencies

No matter how much you care about your plants, there are always things that CAN and WILL go wrong with them in the process of growing. It doesn’t matter if you’re a beginner or a master grower, it is surprisingly easy to slip into a false sense of security with your beloved plants. Truth is, your plants are sensitive beings from seed to harvest.

Generally, most problems associated with cannabis growing fall into three broad categories:

  • Nutrient deficiencies – which can cause necrosis and chlorosis to your plant which is falling and/or yellowing of the leaves;
  • pH fluctuation problems – that are crucial to measure in cases of nutrient deficiency (different nutrients get absorbed by the plants at different pH rates);
  • Pests and diseases – that will show up if a plant is faultily nurtured and watered.

In this guide, we will attempt to identify every symptom that you notice on your plants and address every possible problem that might me associated with it.

Taking care of cannabis plants

Simple Tips for Healthy Plants

Quick tips to help prevent and rectify sick marijuana plants.

Avoid Over/Under Watering your Plants

Dropping water marijuana

Sounds simple enough? You’d be surprised how important that is to your plants (and how many people are doing this wrong)! In general, plants use their roots to absorb oxygen from water. When you overwater your plants you are practically drowning them in a pool of oxygen-less water. On the other hand, under-watering is practically asphyxiating your plants. In both cases, you are killing your own plants and you should probably stop doing that.

Effects of Over/Under Watering

In both cases, the effects on your plants will be the same: the leaves will start curling down and flopping all the way to the stem. Your plant will look lifeless and frail.

Overwatered marijuana plant

Underwatered marijuana plant

What to do

This is one of the most common newbie problems, and not just for cannabis growers. Luckily, its effects are easily reversible. For plants that have been over-watered, you just need to give some time without any water, until things start to stabilize. You can also help your plants by increasing the temperature or aerating their environment by poking a few holes in the soil, to increase the flow of air (if you’re growing in soil, that is). A good way to know whether your plants need water is by touching the topsoil. If it feels dry, then it might be time to pour your plants a drink.

For under-watered plants, you will notice that the pot of the plant will feel significantly lighter when picked up. That’s because all the water inside the soil has been used up. You can even use the “second container” method to determine how heavy your vessel exactly needs to be: just fill a similar second pot with the same (dry) growing medium and use it as a standard to determine just how dry your plant really is.

Temperature Regulation Problems

Marijuana leaves temperature problems

Chances are, your plants’ ancestors have travelled far and wide to be with you. Some strains include genetics that thrived in climates much different than yours. For example, Durban Poison grows on the streets in South Africa but needs special care in the US. Similarly, it doesn’t take much thought to deduct that a plant that thrives in Panama, might not feel all that comfortable in Portland, Oregon. While this is much less of a problem for indoor growers, where temperatures are much more controllable, fluctuations in temperature can play a major role in plant development. Luckily, this is also one of the factors that can be easily monitored and controlled by the grower.

Effects

While this is a multi-layered problem with many variables to take into consideration, the plants generally prefer a temperature around 70-85°F (20-30°C) during the day and they can be quite comfortable with slightly lower temperatures in the night. Younger seedlings in their vegetative stage require a slightly higher temperature.

Colder temperatures might lead to poor phosphorous absorption that can halt the development of your plants. You can easily spot signs of under-temperature plants by a deep-purple pigmentation on the leaves. Some plants that are grown in temperatures under 60ºF (15ºC), can freeze to death overnight. While it is largely a matter of genetics and there are strains that can indeed survive, their development will be severely hindered.

Effects of cold on marijuana plant

Effects of heat on marijuana plant

On the other hand, too hot environments can also lead to problems. You will notice that your plant is too hot when its leaves start cupping (folding). Overheating is usually not fatal (as opposed to colder temperatures), but will also delay plant growth, while leaving it susceptible to mold, bugs and burning of the leaves. Also, terpenes, the cannabinoids that are responsible for the smell and taste of your plants, can be burnt out at high temperatures.

What to Do

The first step in understanding how suitable your environment is for your plants, is by using your senses. Plants generally prefer similar temperatures to us humans, so if your room feels too cold or too hot, it probably is. Other than that very practical advice, you can do lots of things to ensure the optimal temperature for your plants. The very first of which should be to go get a great thermometer.

If your environment is too warm

  • Invest in a proper ventilation system. Not only will you regulate temperatures more effectively, but you will also improve air circulation which is crucial to the well-being of your plants.

Grow room ventilation system

  • Use LED Grow Lights. Their usefulness has been much debated over forums and magazines the last few years, but the general consensus is that a good set of LED grow lights can provide full spectrum lighting for your plants and lower energy costs, while at the same time running at much cooler temperatures. For the best grow lights on the market, consult our in-depth LED grow lights guide.

LED grow lights

  • Modify your plants lighting schedule. Different strains have different lighting habits during different growth stages with which you should become familiar (more research about each strain’s preferred light cycle can be found on our massive strain database.

Marijuana plant lighting schedule

  • Get an A/C unit. Although most of the above methods will most likely fix your heating problems, if issues persist a good old A/C unit might work wonders in regulating the temperature of your grow room.

AC units grow room

If your environment is too cold

  • If your grow room is in a room that can be insulated, insulating it would be your best bet. However, we know that this is not always possible. Therefore, you might need to invest in a dedicated grow box or grow tent (preferable for larger rooms). This should act as a very adequate insulation to your plants. Here on HTG we have extensively covered the pros and cons of both solutions and you can find in-depth articles about all the latest models in the above links.

Grow box marijuana

Grow tent marijuana

  • Proper ventilation is equally important, to distribute heat evenly.
  • Invest in a heater with a thermostat. This is advised for extreme cases only, however if you have to get a heater, be sure that it has a thermostat. Also, never, ever have your heater blow hot air directly at the plants.

Heater with thermostat

Eutrophication (or Nutrient Burn)

Marijuana leaves nutrient burn

As you might have gathered by now, plants love balance. They are sensitive to the extreme lengths over-eager growers can go in order to produce more, faster. In the final part of this chapter, we are going to inspect the problem of feeding your lovelies too much. If you tend to over-feed your plants like an over-protective parent, you’ll end up doing more harm than good. Contrary to what you might instinctively think, young plants do not require a lot of fertilizer. In fact, in the first month of growing, you should only use a quarter of the normal dosage for your plants, and then gradually step it up.

Nutrient burn symptom

Effects

The leaves of your plant start to fold in the middle and feel more hard. You might also notice gray and brown pigments on the blade of the leaf. In severe cases, the leaves turn golden brown and then die.

Nutrient burn brown pigment

What to Do

Be sensible with the amounts of fertilizer you use. If you observe any of the above signs on your plants, cease fertilization for a few days and resume when the symptoms recede. For more severe cases, a thorough wash of the pot with pH regulated water is advisable. Clean the soil with 5x the amount of your pot’s volume (e.g. 25lt of water for a 5lt pot). Pour the water in the pot, one gallon at a time, wait and repeat.

Nutrient Deficiencies

Now that we have covered some of the very basic concepts of plant caring, it is time to delve deeper into the vast topic of nutrient deficiencies that can affect your plants. Nutrients are all-too-important for your plants; they are the basis of their existence and, much like you, the plants need to receive them in a healthy amount, in order to produce their THC filled goodness. Below you’ll find a list of all the nutrients your plant needs in order to survive and flourish.

Essential mineral macronutrients (soil):

  • Nitrogen (N);
  • Phosphorus (P);
  • Potassium (K);
  • Calcium (Ca);
  • Magnesium (Mg);
  • Sulfur (S).

Non-mineral elements derived (air/water):

  • Carbon (C);
  • Hydrogen (H);
  • Oxygen (O).

Fertilizer bags and nutrient supplements, often feature three numbers in their packaging, that indicate the quantity of the three main elements (N, P and K) is contained in the product. The number are always listed in this order: N – P – K.

However, these are not all; there is also a plethora of micro-nutrients that play a variety of roles in plant growth and development:

  • Zinc (Zn);
  • Iron (Fe);
  • Manganese (Mn);
  • Molybdenum (Mo);
  • Chlorine (Cl);
  • Cobalt (Co);
  • Silicon (Si);
  • Boron (B);
  • Copper (Cu).

Although they are called “micro” nutrients and are indeed used in much lower amounts, make no mistake: these minerals are crucial to a plants’ health and many of the problems that we will see in detail below, are directly associated with insufficient amounts of said micronutrients in the growing medium. Generally, it is a good idea to obtain a reliable electronic pH tester, as these measurements are going to prove extremely useful to you during the whole growing process. All nutrient deficiencies are tied to pH level fluctuations both in soil or hydroponic setups, so it is important that you get these right.

pH soil tester

Boron Deficiency

Boron deficiency is the most widespread among plant maladies, but it is also surprisingly uncommon for cannabis plants. However, it can occur and it is best if you know what to do about it. The most common signs of boron deficiency are thick grow tips and golden brown spots on young leaves.

Boron deficiency

Effects

Boron deficiency can severely delay plant growth and lead to distorted growth of new tips, that will eventually lead to their death. The stems of the plant become harsh and the new leaves may fold and swirl.

Boron deficiency folding leaves

Boron deficiency swirling

Boron deficiency effects

Solution

  • Use proper nutrients for your plants. Chances are that your fertilizer or nutrient already contains sufficient amounts of boron to cover your cannabis plant needs. However, the problem might arise nonetheless, especially if you are using reverse osmosis filtered watered on out plants.
  • Adjust the pH to the appropriate levels. Here is where our good friend, the pH testing kit is going to prove useful.
    • In soil-based setups, boron is best absorbed by the roots in the 6.0 – 6.5 pH range (though it is recommended to keep your soil setup below 7.0 at all times).
    • In hydroponic systems, boron is best absorbed by the roots in the 5.5 – 6.2 pH range (in hydro, it’s usually advised to keep the pH between 5.5 – 6.5 at all times).
  • Keep your plants damp. The problem might arise in extremely dry conditions, so keep watering your plants properly and use a humidifier if need be. Generally, if the air humidity is below 25% you might have a problem.

Spray cannabis plants

  • Be ever vigilant. Just because you followed all of the above instructions, doesn’t mean that you should slip into a sense of false security; keep watching your plants closely and observe whether the symptoms disappear.

Tips from Growers

“When I spray my plants, on certain days I’ll spray them with the res water. Other days, fresh PH balanced water. Instead of just topping (as is done when not spraying) up my reservoir directly, I’ll spray balanced water until the res is full. My res gets 1/6 the fertilizer recommended for dirt. I have set this example as I have used other ferts and some of them are hotter than others. I keep my pH at 5.5-6.3. My mother plants get it after the budders are done with it (every five days). If you keep your plants on a schedule that works good for that location, you won’t have these types of deficiency problems. Hydro problems are far easier to fix than dirt problems.”

“One of the ways to fix a boron deficiency is to either foliar spray or water regular. Treat with one teaspoon of Boric acid (sold as eyewash) per 4 liters of water.”

Calcium Deficiency

Calcium deficiency marijuana

Calcium is (obviously) caused by the lack of calcium within the growing medium. More often than not, it is a result of insufficient transpiration (=the process by which moisture is carried through plants from roots to small pores on the underside of leaves). If not enough calcium is transported to the outer layer of the plant, the tissue is affected by calcium deficiency. This can be caused by inadequate watering or unnecessary usage of potassium or nitrogen-rich fertilizers.

Effects of Calcium Deficiency

Calcium deficiency can lead to an extremely acidic environment that can, in turn, develop into magnesium and iron deficiencies, while simultaneously delaying the growth of the plants. Cannabis plants affected by calcium deficiency may have very fragile and/or decaying stems. They also become very sensitive to heat and flowering is severely hindered.

Calcium deficiency marijuana leaves

Calcium deficiency marijuana detail

Calcium deficiency marijuana

Solution

  • It is important that your cannabis plants have sufficient levels of calcium. Therefore, use of supplements is not uncommon (although it should be practiced with care, as too much calcium might retro-react with other nutrients).
  • Avoid the excessive usage of potassium and nitrogen-rich fertilizers.
  • Use Dolomite Lime

A good way to supplement calcium in your organic or soil setup, is by using a product called “Dolomite Lime.” Dolomite is a great source of calcium and magnesium and can be mixed with your soil. The best thing about dolomite is it works slowly over the course of a few months. It has a neutral pH of about 7.0 and helps keep soil at the correct neutral pH range which is optimum for cannabis growth. You can order Dolomite Lime online, but it is easier to pick it up at your local gardening shop. If possible, try to get a better-quality dolomite.

How to Use: For indoor grows, add 6-7 teaspoons of fine dolomite lime to each gallon’s worth of soil. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with pH’d water. After getting the soil wet, mix the soil well and wait a day or two to let it settle. Then check the pH and add it to your plants. When growing outdoors, just follow the manufacturers instructions.

  • Adjust the pH to the appropriate levels.
    • Calcium stops being absorbed by soil at pH levels of 2.0- 6.4. On the other hand, it is best absorbed best in soil at a pH level of 6.5-9.1.
    • For soil-less setups, calcium is absorbed best at pH levels of 5.4-5.8 and stops being absorbed at 2.0 – 5.3.

Tips from Growers

“When addressing calcium deficiency, definitely keep your pH below 6.0 at all times in hydro. Calcium uptake is better with pH at the higher end of the acceptable hydro range.”

Copper Deficiency

Copper deficiency marijuana

Copper is regarded by many gardeners as a toxic element that doesn’t have a place in marijuana (or indeed any plants’) growth. This is not entirely wrong; too much copper can actually poison the plants. However, a little amount is necessary for healthy growing plants. Most soils on the market are deficient in copper by default, so you might need to introduce it to your plants yourself, only after your growing medium has been professionally tested and measured for copper deficiency.

copper is, in fact, important to the health of the plants and helps with building the stems and the branches of new growths. Furthermore, it contributes on carbohydrate breakdown and oxygen reduction.

Effects of Copper Deficiency

We have already established that too much copper will kill your plants pretty fast. On the other hand, plants that are afflicted by copper deficiency show the following symptoms

  • A lack of growth or irregular growth;
  • A slight, bluish tint on the green leaves;

Copper deficiency marijuana bluish tint

  • Plants may have a hard time showing maturity in vegging stages;
  • Drooping in the newer growths;
  • Leaves on the top of the plant may show veinal chlorosis (bleaching of the veins);
  • Growth and yield will be diminished along with spots on the leaves that are necrotic.

Copper deficiency marijuana potato

Copper deficiency marijuana signs

Copper deficiency marijuana bleaching

If severe copper deficiency happens at an early stage of the flowering of the plant, the affected leaves become less effective at photosynthesis, harming the quality of the end product.

Solution

  • As always adjust the pH to the appropriate levels.
    • In soil: copper gets locked out of soil growing at pH levels of 2.0- 4.5. Copper is absorbed best in soil at a pH level of 5.0-7.5.
    • For soil-less setups: copper is not absorbed by hydro and soil-less mediums at pH levels of 6.5-9.0. Copper is absorbed best in hydro and soil-less mediums at pH levels of 2.0-6.0. Best range for hydro and soil-less mediums is 5.0 to 6.0.
  • Another way to treat a copper deficiency is by foliar feeding with copper sulphate, Cu sulfate and Cu chelates. Those three can also be used in soil. Basically, any nutrient that contains copper can solve this deficiency pretty quickly. Just be careful not to put too many nutrients on your grow, or else you will have a nutrient burn problem.

Magnesium Deficiency

[insert- magnesium-deficiency-marijuana]

Magnesium is a nutrient that is especially useful in the photosynthetic process. Magnesium is responsible the formation of the central atom of chlorophyll. Therefore, the absence of sufficient amounts of magnesium means that plants begin to degrade the chlorophyll in the old leaves (magnesium is a mobile nutrient, which practically means that it can be moved from old leaves to new ones). If left untreated, a magnesium deficiency can quickly spiral out of control and cause loss of leaves as the plant will transfer magnesium out of older leaves to the newer sprouts. That’s pretty much the reason why magnesium deficiencies typically manifest themselves towards the bottom of the plant where the older leaves are.

Effects of Magnesium Deficiency

  • Chlorosis: a very distinct yellowing between leaf veins, which will stay green (as opposed to nutrient burn cases) giving the leaves a mottled appearance;

Magnesium deficiency marijuana chlorosis

  • Crispy and frail leaves, that have yellow spots within their margins;

Magnesium deficiency marijuana leaves

  • Magnesium is fundamental in steadying ribosome structures. Therefore, a lack of magnesium causes depolymerization of ribosomes, that can lead to pre-mature aging of the plant. After protracted magnesium deficiency, necrosis and dropping of older leaves occurs. Plants deficient in magnesium also produce smaller, woodier fruits.

Magnesium deficiency marijuana necrosis

Solution

  • Magnesium deficiency can be misidentified as zinc or chlorine deficiency, a virus, or as natural aging, so notice the details on your plants and cross-examine it with the symptoms on this list. Adding Epsom salts (diluted to 8.5 oz. per 2.2 gal. of water) or crushed dolomitic limestone to the soil can help address magnesium deficiencies.
  • Use Dolomite Lime:

A good way to supplement magnesium in your organic or soil setup, is by using a product called “Dolomite Lime.” Dolomite is a great source of calcium and magnesium and can be mixed with your soil. The best thing about dolomite is it works slowly over the course of a few months. It has a neutral pH of about 7.0 and helps keep soil at the correct neutral pH range which is optimum for cannabis growth. You can order Dolomite Lime online, but it is easier to pick it up at your local gardening shop. If possible, try to get a better-quality dolomite.

How to Use: For indoor grows, add 6-7 teaspoons of fine dolomite lime to each gallon’s worth of soil. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with pH’d water. After getting the soil wet, mix the soil well and wait a day or two to let it settle. Then check the pH and add it to your plants. When growing outdoors, just follow the manufacturers instructions.

  • Adjusting the pH to the appropriate levels.
    • In soil: magnesium gets locked out of soil growing at pH levels of 2.0-6.4. Magnesium is absorbed best in soil at a pH level of 6.5-9.1.
    • For soil-less setups: magnesium gets locked out of hydro and soil-less mediums at pH levels of 2.0-5.7. Magnesium is absorbed best in hydro and soil-less mediums at pH levels of 5.8-9.1. Best range for hydro and soil-less mediums is 5.0 to 6.0.

Tips from Growers

“A quick surefire sign for Mg deficiency is to mix up 1/4tsp MgSO4 (Epsom salt) to a gallon of clean water, adding a drop or four of a non-antimicrobial dish detergent (surfactant), apply that as a foliar, being sure to get it well saturated on the undersides of the leaves. If it greens up quickly, you need to supplement a little Mg in the mix. If not, it’s more likely it was a nitrogen deficiency.”

Manganese Deficiency

Manganese deficiency marijuana

Manganese (pronounced manga-knees) helps enzymes break down chlorophyll and photosynthesis production. It also collaborates with plant enzymes to reduce nitrates before producing proteins.

Effects of Manganese Deficiency

Young leaves of plants that are manganese deficient are usually spotted (mottled) yellow and have brown areas. Dead (Necrotic) yellow spots are formed on the top leaves, while the lower ones may have gray dots.

Other symptoms can include yellowing of leaves while the leaf veins can stay green, much like the case in magnesium deficiency. Magnesium deficiency can also produce a patchy effect on the leaves. As the plant gets newer growths, it will seem to get over the problem on its own because younger leaves may appear unaffected. However, on the top of the leaves, chocolate-colored spots can appear, while the severely affected areas of the leaves turn brown and wither.

Manganese deficiency marijuana brown spots

Manganese deficiency marijuana leaves

Manganese deficiency marijuana yellowing

Solution

When addressing manganese deficiencies, it is important to know that too much of it will cause an iron deficiency on your plants and weaken them significantly.

  • Adjusting the pH to the appropriate levels.
    • In soil: manganese gets locked out of soil growing at pH levels of 2.0-5.0. Manganese is absorbed best in soil at a pH level of 5.5-6.5.
    • For soil-less setups: manganese gets locked out of hydro and soil-less mediums at pH levels of 2.0-4.5. It is absorbed best in hydro and soil-less mediums at pH levels of 5.0-5.6. Best range for hydro and soil-less mediums is 5.0 to 6.0.
  • Foliar feed with any chemical fertilizer containing manganese, or mix it with water and water your plants with it. Any Chemical/Organic nutrients that have manganese in them will fix a manganese deficiency (be careful when using chemical nutrients; only mix them at half the strength to avoid nutrient burn). Other nutrients contain manganese are: manganese chelate, manganese carbonate, manganese chloride, manganese dioxide, manganese oxide, manganese sulfate, which are all fast absorption. Garden manure and greens and are both good sources of manganese and are medium/ slow absorption.

In case you add excessive chemical nutrients, follow the instructions on solving nutrient burn.

Molybdenum Deficiency

Molybdenum deficiency marijuana

Molybdenum deficiency is not all that common among cannabis plants and its symptoms might look like a nitrogen deficiency at first. It has been observed to appear more in marijuana strains that change colors in colder temperatures.

Effects of Molybdenum Deficiency

The symptoms will start with middle leaves that turn yellow. The signs of the deficiency will move toward the sprouts and younger leaves as they grow warped and coiled. Leaves might also turn pale and have a charred look. Their growth will be significantly set back and older leaves that have experienced chlorosis, will have rolled leaves, slowed growth, and reddish tips that curl inward.

Molybdenum deficiency marijuana charred look

Molybdenum deficiencies are usually present when there are also insufficient amounts of sulfur and phosphorus, so you might want to take a look into that as well.

Molybdenum deficiency marijuana leaves

Molybdenum deficiency marijuana flower

Solution

  • Adjusting the pH to the appropriate levels.
    • In soil: molybdenum is best absorbed by the roots in the 6.0 – 7.0 pH range
    • For soil-less setups: molybdenum is best absorbed by the roots in the 5.5 – 6.5 pH range.
  • Foliar feed with nutrients that contain molybdenum. Any Chemical/Organic nutrients that has molybdenum in it will fix a manganese deficiency (be careful when using chemical nutrients; only mix them at half the strength to avoid nutrient burn).

Iron Deficiency

Iron deficiency marijuana

Iron is an important component of the plants’ enzymes and is also important for the transportation of electrons while photosynthesis is happening.

Effects of Iron Deficiency

As we mentioned above, a cannabis iron deficiency looks like a magnesium deficiency. The key difference is that an iron deficiency will affect newer/top leaves, where a magnesium deficiency affects older/lower leaves. Iron deficiency usually manifests itself as an interveinal chlorosis of the youngest leaves, evolves into an overall chlorosis, and ends as a totally bleached leaf. The faded areas often evolve necrotic spots. The effects of the iron treatment will be immediately visible upon application.

Iron deficiency marijuana chlorosis

Iron deficiency marijuana bleached leaf

Iron deficiency marijuana closeup

Solution

  • Solving iron deficiency might actually a little bit trickier than the others. Iron reacts with many of the components that nutrient solutions are made of. If you are not careful, you might end up creating new problems in trying to solve the iron deficiency. For example: if you add to much iron without adding enough phosphorus, you can contribute to a phosphorus deficiency. You will be able to see the effects of the recovery stage as the veins will revert to their bright green color.
  • Adjusting the pH to the appropriate levels.
    • In soil: iron gets locked out of soil growing at pH levels of 2.0-3.5. Iron is absorbed best in soil at a pH level of 4.0-6.5.
    • For soil-less setups: iron gets locked out of hydro and soil-less mediums at pH levels of 2.0-3.5. Iron is absorbed best in hydro and soil-less mediums at pH levels of 4.0- 6.0.
  • Watch out for root problems with your plants. Iron deficiencies can show up with the plant is having root issues or if the plant is excessively watered, even when the pH measurements are right. There is a reason we listed proper watering among the very basics a grower can do. It’s a simple process that can save you a lot of trouble.
  • If you believe that you have an iron deficiency even though you get correct pH measurements, flush your system with clean, pH’d water and add a supplement that contains iron, calcium and magnesium.

Tips from Growers

“Add a few rusty nails to your water/ res. If it’s iron deficient, that should fix them.”

“I added lemon juice and brought the pH down, it’s currently at about 6.0 and gave them full dose nutrients in water. The stalks that were so yellow having gone back to a healthier green color so it seems to be working. I also removed the lowest pair of leaves.”

Phosphorus Deficiency

Phosphorus deficiency marijuana

Phosphorous is an essential component of cannabis plants development. It helps in root development and affects the vigor of the plant. It is one of the most vital elements in flowering too, as it helps germinate seedlings. Furthermore, phosphorus is a basic plant nutrient; it is needed in large amounts, hence it is categorized as a macronutrient. Phosphorus is also a crucial nutrient in the plants’ reproductive stages. Without this element, the plants will have a lot of problems blooming without proper levels of phosphorus.

Effects of Phosphorus Deficiency

Identifying the symptoms of phosphorus deficiency might be trickier than it sounds, as the visual effects on the plants are usually hard to spot. Perhaps the most characteristic giveaway is the fact that your plants’ development might have been halted and they might be dwarfed. Afflicted plants can also exhibit brownish leaves; as the condition works its way inwards a bit causing the part of the leaves to curl upwards. Fan leaves will show dark purplish and yellowish tones along with a dullish blue color to them.

It is also easy to mistake phosphorus deficiency for fungus problems. The key difference is that in phosphorus deficiency, the damage occurs at the end of the leaves. The sides of the leave have a frail feeling to it as if it had a pH problem.

Phosphorus deficiency marijuana leaf

Phosphorus deficiency marijuana curl upwards

Phosphorus deficiency marijuana progression

Solution

  • Adjusting the pH to the appropriate levels.
    • In soil Phosphorus gets locked out of soil growing at pH levels of 4.0-5.5. Phosphorus is absorbed best in soil at a pH level of 6.0-7.5.
    • For soil-less setups: Phosphorus gets locked out of hydro and soil-less mediums at pH levels of 6.0-8.5. Phosphorus is absorbed best in hydro and soil-less mediums at pH levels of 4.0- 5.8.
  • Watch out for cold temperatures. As we mentioned at the start of this article, proper temperature control can save your plant’s lives. Colder temperatures (lower than 60°F (15°C), as well as extreme temperature fluctuations, can make it harder for the plant to absorb phosphorus. Cannabis plants are more likely to show signs of a phosphorus deficiency when the temperature drops too low, or if they go through a cold spell.
  • Provide your plants with the right nutrients. All of the nutrients in the market contain phosphorus. Besides chemicals, there are several other options that can act as a phosphorus source for your plants: bone meal, worm castings, (gradual absorption), fish meal (medium absorption), soft rock phosphate (medium absorption).

Tips from Growers

“Some phosphorus deficiency during flowering is normal, but too much shouldn’t be tolerated. Red petioles and stems are a normal, genetic trait for many strains, plus it can also be a sign of N, K, and Mg-deficiencies, so red branches are not a definite sign of P-deficiency. Too much P can lead to iron deficiency.

Purpling: accumulation of anthocyanin pigments; causes an overall dark green color with a purple, red, or blue tint, and is the common sign of phosphate deficiency. Some plant species and varieties respond to phosphate deficiency by yellowing instead of purpling. Purpling is natural to some healthy ornamentals.”

Potassium Deficiency

Potassium deficiency marijuana

General Information about Potassium

Potassium is yet another important component for plant growth and development. Sufficient amounts of potassium in your plants means that they will grow sturdy and thick stems. It also aids with disease-resistance, water respiration, as well as photosynthesis. Basically, it is necessary for all activities having to do with water moving within the plant. Potassium is needed for all stages of growth, especially important in the development of buds.

Effects

Potassium deficiencies are practically a non-issue among hydroponic setups. That’s because it mainly occurs on outdoor soil grows. Problems with potassium deficiency can appear even when the soil is well fertilized and rich. Insufficient amounts of potassium in your plants can cause the plants’ leaves to grow at reduced speed. Afflicted leaves show a scorched tip and edges around the leaves. Branches are becoming frail and can snap easily.

Potassium deficiency has almost the same symptoms as iron. As we mentioned above, for potassium, the tips of the leaves twist and the edges burn and die. Older leaves may show a red color and leaves could curl upwards. You can also spot necrosis, that can happen on the margins of larger fan leaves. Older leaves will exhibit different patterns of color and turn yellow between the veins. The plants’ overall development is halted, especially during vegetative stage. Too little amount of potassium also slows the growth of buds during flowering stages. Relative humidity is key in preventing potassium deficiencies: if humidity is very low, potassium deficiency is almost a certainty.

Finally, potassium can get poorly absorbed when combined with too much calcium or ammonium nitrogen; cold weather doesn’t help either. Having too much sodium (Na) causes potassium to be displaced.

Potassium deficiency marijuana yellowing

Potassium deficiency marijuana early

Potassium deficiency marijuana brown edges

Solution

  • Adjusting the pH to the appropriate levels.
    • In soil: potassium gets locked out of soil growing at pH levels of 4.0-5.5. Potassium is absorbed best in soil at a pH level of 6.0-9.5.
    • For soil-less setups: potassium gets locked out of hydro and soil-less mediums at pH levels of 4.0-4.5, 6.0-6.5. It is absorbed best in hydro and soil-less mediums at pH levels of 4.7-5.3, 6.7-8.5.
  • Watch out for cold temperatures. As we mentioned at the start of this article, proper temperature control can save your plant’s lives. Colder temperatures (lower than 60°F (15°C), as well as extreme temperature fluctuations, can make it harder for the plant to absorb phosphorus. Cannabis plants are more likely to show signs of a phosphorus deficiency when the temperature drops too low, or if they go through a cold spell.
  • Provide your plants with the right nutrients. All of the nutrients in the market contain potassium, so if you are a grower, you probably have a good source of the component somewhere around your grow room.
  • Potassium deficiencies might also be confused with light burns. See our temperature control section on this article for more information.

Tips from Growers

“I always use p-k 13/14 in flowering, this really does help with flower production and the plants use of potassium.”

“You can add potassium naturally by adding a liquid solution of wood ash, chicken manure or semi-liquid manure but be careful to avoid nutrient burn. Grape and vine extracts also contain a lot of potassium.”

Sulfur Deficiency

Sulfur deficiency marijuana

Sulfur is essential for root growth, chlorophyll supply and plant proteins. Just like iron, sulfur is a mobile nutrient, that moves slowly in the plant. Hotter temperatures make sulfur harder to absorb, like iron. However, unlike iron, sulfur is distributed evenly throughout the plant, mainly in the big fan leaves. Sulfur is also a very useful element in vegetative growth.

Effects of Sulfur Deficiency

The symptoms of sulfur deficiency are identical to the chlorosis caused by nitrogen deficiency. However, in sulfur deficiency the yellowing of the leaves is much more constant over the entire plant, including the younger leaves. The roseate color often found on the base of the leaves and the petioles and is much less vivid than the one found in nitrogen deficiency. Advanced sulfur deficiency can be identified by the brown grazes and/or necrotic spots that often develop along the petiole, in which case the leaves tend to become stiffer and often curled and brittle.

Sulfur deficiency marijuana chlorosis

Sulfur deficiency marijuana progression

Sulfur deficiency marijuana sample

Solution

  • Adjust the pH to the appropriate levels.
    • In soil: Sulfur gets locked out of soil growing at pH levels of 2.0-5.5. Sulfur is absorbed best in soil at a pH level of 6.0 – 9.5.
    • For soil-less setups: Sulfur gets locked out of hydro and soil-less mediums at pH levels of 2.0-5.5. Sulfur is absorbed best in hydro and soil-less mediums at pH levels of 6.0 – 9.5.

Zinc Deficiency

Zinc deficiency marijuana

Zinc has a lot of functions in a plant’s health. First of all, zinc helps the plants reach optimal size and maturity, as well as the production of leaves, stalks, stems and branches. Zinc is a vital nutrient in many enzymes and the growth hormone auxin. Deficiencies in auxin levels can cause reduced development speeds. zinc is important in the formation and activity of chlorophyll and cannabis plants that have a good level of zinc, can handle long droughts.

Effects of Zinc Deficiency

In the early stages of zinc deficiency, younger leaves become yellowish and pitting develops in the interveinal surfaces of the mature leaves. Zinc deficiencies on some plants might manifest themselves with blemishes and bleached spots (chlorosis) between the veins. It appears on the older leaves first and then moves on to the immature leaves. Then, it will affect the sprouting points of the plant.

Zinc is an immobile nutrient, so the symptoms will happen and stay mainly in the newer sprouts. Plants that are afflicted by zinc deficiency usually produce meager yields, develop short shoots and have a knot of small distorted leaves near the tips.

Zinc deficiency marijuana chlorosis

Zinc deficiency marijuana yellowing

Zinc deficiency marijuana withering

Solution

  • Adjust the pH to the appropriate levels.
    • In soil: Zinc gets locked out of soil growing at pH levels of 4.5-4.7, 7.5-9.5. Zinc is absorbed best in soil at a pH level of 5.0-7.0.
    • For soil-less setups: Zinc gets locked out of hydro and soil-less mediums at pH levels of 5.7-8.5. Zinc is absorbed best in hydro and soil-less mediums at pH levels of 4.0-5.5.
  • Provide your plants with the right nutrients. All of the nutrients in the market contain zinc, so if you are a grower, you probably have a good source of the component somewhere around your grow room.
  • Be careful not to overwater your plants, as zinc deficiencies usually show up in plants that have root problems.

Nitrogen Deficiency

Nitrogen deficiency marijuana

Final in this series about nutrient deficiencies is nitrogen deficiency. Nitrogen in itself is one of the essential components for the proper development of cannabis. It is responsible for producing chlorophyll and amino acids, and it’s also indispensable to the process of photosynthesis. Nitrogen is also the basis for the tissue of the plant, meaning that development would stop immediately after a deficiency starts to manifest.

Effects of Nitrogen Deficiency

Leaves will start to turn pale green, then yellow, and start to die off as the remaining nitrogen in the plant moves towards the new growth. As the deficiency progresses up the plant, only new growth at the top will appear to be green. The lowest leaves will start to turn pale and eventually wither. Plants that suffer from nitrogen deficiency might also develop smaller leaves, while growth rate decreases. Branches and petioles gain a slight red or purple hue. If you notice your lower cannabis leaves turning yellow in the vegetative stage or in the beginning part of the flowering stage, your plant may be experiencing a nitrogen deficiency which will need to be addressed. It is not good if your cannabis plant is showing signs of an advanced nitrogen deficiency while still in the vegetative stage. It’s usual to lose a few yellow leaves off the bottom of your plant here and there, especially with large plants. But if you are losing a significant amount of yellow leaves, and the yellowing seems to be moving up the plant quickly, then you have a problem.

Nitrogen deficiency marijuana closeup

Nitrogen deficiency marijuana pale

Nitrogen deficiency marijuana wither

Solution

  • Adjust the pH to the appropriate levels.
    • In soil: nitrogen gets locked out of soil growing at pH levels of 4.0- 5.5.
    • For soil-less setups: nitrogen gets locked out of hydro, soil-less mediums at the levels of 4.5-5.0. Nitrogen has the best absorption rate at a pH of 5.5 to 8.0.
  • Provide your plants with the right nutrients. There are many pre-mixed nutrients on the market, which contain nitrogen. Alternatively, you can use some of the following organic supplements that are high on nitrogen:
    • Calcium nitrate (CaNO3)/ Foliar Feeding;
    • Urine;
    • Fish emulsion;
    • Cottonseed meals;
    • Alfalfa;
    • Manure;
    • Feather meal;
    • Fish meal.

Tips from Growers

“Avoid excessive ammonium nitrogen, which can interfere with other nutrients. Too much N delays flowering. Plants should be allowed to become N-deficient late in flowering for best taste.

Bugs and Pests on Cannabis

Bugs and Pests

Put simply, pests and bugs are the nemesis of growers. Here on HTG we have addressed the issue in the past. It is practically impossible not to encounter them in your grow environment. For bugs, your marijuana growing setup is like the Garden of Eden: a friendly environment, abundant with food and relatively safe from predators. That is of course until you go all Sherlock Holmes on them with your 8X magnifying glass (that’s the minimum magnifying power you’ll need to spot them critters). It’s best to check for pests under your plant’s leaves. Alternatively, you might need to try to spot slight stains on the top of the leaves in order to realize they’re even there. Most of them are incredibly tiny, so there is a good chance you’ll miss them if you’re not too careful.

If you’re thinking chemical pesticides, you’d better forget it. Contrary to other plants, cannabis does not like chemicals (not to mention your end product will be poisoned, ergo un-smokeable). Luckily, there are many organic alternatives, like neem oil, pyretine or pine soap solution. You can also make your own all-purpose natural pesticide from red pepper, chili powder or soap and water. Below, we will list all the major threats to your plants and their feeding habits, as well as ways to get rid of them.

  • Tetranychus urticae (Spider Mites, Broad Mites);
  • Fungus Gnats;
  • Whiteflies;
  • Thrips;

For flying pests, carefully placed traps around your grow room might be a pretty good prevention measure, however, nothing can replace regular inspection with a magnifying glass. Let’s take a (much) closer look at the insects one by one.

Mites

Spider mites cannabis

Broad mites cannabis

Mites are orange-toned arachnoids, and they are almost inconspicuous: less than 0.5 mm long. They are one of the worst infestations that can happen and usually they occur from inadequately sterilized soil (see: cheap soil) or if you move outdoor plants indoors. Usually, these pests occur when the humidity is below 80%. If you notice fine spider webs with larvae among the leaves of your plants, then you are certainly dealing with spider mites (and the infestation is already at a very advanced stage). If your cannabis plant’s leaves are taking a rough yellow undertone and are starting to fall off, it is probably infested with spider mites.

Spider mites webbing

Mites love dry and warm environments, so to exterminate them, it is often sufficient to spray your plants regularly and maintain a healthy level of ambient humidity. If you have already noticed that some of your plants are infected by mites, remove them from your grow room immediately, to avoid spreading the infection and apply an organic pesticide (see above for more information), paying extra attention to the underside of the leaves. Raising humidity and lowering the temperature also helps a lot with mites and will often be sufficient in reducing their population. However, you should bear in mind that mites are extremely resilient and it will take a lot of work to take them out. Check regularly, even long after you think the problem disappears. Also, never let pets around your plants: they can infect them with mites.

Fungus Gnats

Fungus gnats marijuana

Fungus gnats are a common nuisance for soil cannabis growers. They appear on over-watered plants, thriving in the humid and decaying conditions that careless growers have created for them. Higher temperatures and a wet top soil, guarantees that you will deal with fungus gnats sooner or later. Fungus gnats love to lay their eggs on the wet soil. These eggs later develop into larvae, that like to gnaw on whatever they come across. Their insatiable hunger can deal a lot of damage to your plants’ roots.

Fungus gnats are especially threatening to younger plants and should be addressed as soon as you realize that they have infected your plants’ soil. Unlike other pests, fungus gnats are easy to spot. While adult gnats are not so much of a threat, they do spread diseases to your plants and they are almost certain to have laid their offspring in your wet cannabis plants’ topsoil. Obviously, the best way to avoid fungus gnats, is to avoid over-watering your plants. That is enough to prevent them from ever bothering your plants. If you have already been infected, there are some ways you can get rid of them.

Fungus gnats symptoms

  • Fill your grow area with yellow sticky surfaces. Fungus gnats love yellow. So these traps will help you measure your effectiveness (you will be able to see all trapped gnats).

Fungus gnats yellow traps

  • Don’t water your plants for a while. Before you start applying insecticide over your soil, you’ll want to exterminate all larvae. There is no better way of doing this, than drying out your topsoil.
  • Blow air directly over your marijuana plants. Just use a fan or any other device with air-blowing properties. Gnats will find it difficult to fly around your plants and the air will dry out your soil.

Whiteflies

Whiteflies pest cannabis

Whiteflies live on the undersides of cannabis leaves and love to chomp on the plant leaves. Although they are significantly smaller than regular fruit flies (also they are, quite obviously, white), they still very capable of spreading dangerous diseases to your plant. This airborne threat can ruin your harvest if left untreated.

Whiteflies can be prevented by sticky traps all over your grow room. If you notice that they have started infesting your leaves, spraying them with neem oil will usually do the trick. Also, soap and water is considered to be an effective home remedy, like thinned garlic and onion juice as a foliar spray. Diluted SM90, a commercial wetting agent, is a good way to control whiteflies

Thrips

Thrips cannabis plants

Although barely visible, thrips can mean a lot of trouble for your plants. They reproduce in a menacingly fast rate and that makes them very difficult to deal with. They have little piercing mouths that suck the sap right out of the leaves of your plant, turning them white. So, if you notice that your leaves looked like they had all the life sucked right out of them, this is because exactly that happened. Also, their condition is not reversible, meaning that if the infestation is left untreated, thrips will kill your plants. Another way to spot thrips is by the excrement they produce on the leaves, which is black, with a tint of green. Finally, thrips can transfer viruses to your plants.

A surefire way to repel thrips (for outdoor grows) is to use garlic. Also, it has been found that the color yellow attracts the thrips and should be advised not to have this color around your grow. If you have already been infected, spray them with neem oil or use lady bugs against them. In severe cases of infestation, you need to use biological warfare, like pyrethrin-based insecticides.

Aphids

Aphids marijuana pests

Much like thrips, aphids are extremely tiny, meaning that spotting them might be a challenge in itself. Generally, they like hiding underneath the leaves and suck the nutrients off leaves. This causes a very noticeable discoloration to the leaves, which turn yellow and wither. Aphids can also carry viruses and diseases transmittable to plants. They seem to thrive in environments around 60-80ºF (15-25ºC). Like all of the pests feeding on plants, they produce excrement (honeydew), that can act as a magnet to other bugs and ants, creating an additional headache to growers.

Although ladybugs tend to naturally solve the problem, there are several home remedies you can implement to reduce aphid infestation:

  • Tomato leaf spray. Immerse one to two cups of chopped tomato leaves in two cups of water and allow it to steep overnight. Dry the leaves through a sieve or cheesecloth into a spray bottle. Add some more water and spray your marijuana plants (especially underneath the leaves).

Tomato leaf spray

  • Garlic oil spray. We have already referred to diluted garlic as an effective all-purpose home remedy. You can make it easily by adding three cloves of finely sliced garlic to two teaspoons of mineral oil and let it soak for 24 hours. Then pour it through a sieve into a gallon jug of water and add one teaspoon liquid dish detergent. Then add the final product to a spray ahead. It should be noted that this mixture is rather strong and that you should apply with care: find an area of your plant and test it first. If you notice any damage on your plant, dilute the mixture some more until you hit the sweet spot.

Garlic oil spray

Keeping your Marijuana Plants Healthy

Many of the different conditions that you may come across bear similar symptoms. That makes identifying the problem a real headache and can distract you from using a suitable targeted approach. Luckily, this guide covers all of the special aspects of every condition and will hopefully help you maintain a healthy garden.

Although pests, deficiencies and diseases can be encountered at every stage of the growing process, your best course of action is always prevention. Cannabis plants are in most cases very delicate and if you undertake the task of growing them, you should be advised that big, plentiful yields and unforgettable highs are just the reward of love and dedication towards your plants. Whether you’re a beginner or a pro, if you are indeed growing responsibly, you’re certain to catch the best kind of bug: the habit of personally crafting and enjoying one of nature’s most precious gifts to humanity.

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2 thoughts on “Marijuana Leaf Symptoms and Nutrient Deficiencies – Sick Plants

  1. stormy says:

    This site is amazing. I am a professional in the gardening world, major. And this site is phenomenal!! Who the heck produces this site…is it JORGE CERVANTES??? Sure sounds like you and your encyclopedia that I use for everything, not just Cannabis. My goodness, I am a professional that is very impressed and will be using and sending this site to many others.

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