Cannabis plants are incredibly rewarding to grow. However, the problem with growing a plant is just that – you have to grow it. Even the easiest-to-grow plant can fall prey to a wide variety of pests, diseases, nutrient deficiencies, and problematic growing conditions. Troubleshooting cannabis plants can be tricky, but with a solid resource guide, most cannabis plant problems can be easily fixed. Here’s how to handle some of the most common problems you might face with your cannabis plants.
Common Signs of Environmental Stress and How to Fix Them
The easiest problems to fix are the ones that you might be making. If you’re growing plants inside, you’re in charge of every aspect of their environment. Fixing those problems can be as simple as getting an extra light!
Heat stress is the result of warmer conditions than cannabis plants can tolerate. The excess heat can result in water leaving the plant too quickly and the breakdown of the photosynthetic process.
Symptoms: Leaves pointing upward, curling inward like a taco shell, or turn brown and crispy.
Solution: Turn down the temperature and water regularly. Moving lights away from the plants, adding a fan to your indoor garden, or improving ventilation all help. Your plants can recover fully from this, depending on extent of heat stress.
The plants that most growers want to harvest are female cannabis plants. These are the plants that grow buds, where the highest level of cannabinoids are found. Hermaphrodite plants are caused when male plants mix into your crop resulting in pollination and the formation of seeds. Hermies are bitter and contain significantly lower levels of cannabinoids, so naturally, you’ll want to avoid this.
However, sometimes female cannabis plants can become hermies without pollination. This is caused by disease, inconsistent flowering light periods, and heat stress.
Symptoms: “Bananas,” AKA long curved growths, or pollen sacs instead of female pistils. You cannot tell if this is happening until the flowering or pre-flowering stage at the earliest.
Solution: Prevent hermies by keeping your plants healthy, respecting their light-dark cycles, and avoiding big temperature swings. Once you have spotted a male plant or a hermie, remove the male plants or sections of plant. They will never grow buds, so you will not be able to harvest them. They also may pollinate your female plants, which you want to avoid.
Light burn is the plant equivalent of sunburn. While it is unusual, if plants are kept too close to their grow lights, it’s possible to exceed the amount of light that a cannabis plant can photosynthesize. The extra light radiation then burns the plant.
Symptoms: Leaves closest to the light source turning yellow and pointing upward. Leaves don’t fall off, however. Not to be confused with nitrogen deficiency, where leaves yellow, wilt, and fall off.
Solution: Move grow lights further away from the plant. Leaves may not recover, but the plant should be fine.
Nutrient burn occurs when there is too much fertilizer in the soil, resulting in nutrients blocking the flow of water through the plant.
Symptoms: Bronze/brown “burns” at the tip of leaves, due to lack of water flow in the plant. If the burn progresses, the brown moves inward on the leaves, which start to curl and crisp.
Solution: Stop using fertilizer if you’re adding it to the water. Flush out any watering system you may be using with pure water, and be slow to add fertilizer back to your rotation. Browned leaves will not recover, but the plant should be fine and brown will cease to spread.
If your plants are getting too much water, they aren’t getting enough oxygen. You also invite other problems, like root rot.
Symptoms: Drooping, wilting leaves after watering. The entire leaf will curl down. Possible yellowing in the leaves if overwatering is chronic.
Solution: Allow the root ball to dry all the way out before watering again. When the cannabis plant stops looking wilted, slowly reintroduce regular waterings, spaced further apart.
If using a hydroponic system, better aerate the water.
Cannabis plants need the pH of their soil to remain stable to efficiently absorb nutrients. Fluctuations stress the plant and cause spotting in the leaves. This is more likely in hydroponic systems, but sometimes happens in soil as well. Ideal pH is 6.2-7.0 for soil, and 6.2 to 6.5 for hydroponic systems.
Symptoms: Tan or brown spotting on leaves toward the bottom of the plant. Spotting occurs on the inner part of the leave, along veins.
Solution: Test the pH of the growing medium regularly, to see when and which way pH is fluctuating. Use vinegar and baking soda or a commercial product to adjust pH.
Not enough water can result in your plants’ crisping and dying of thirst.
Symptoms: Wilting, soft, papery or wrinkled leaves that look better after watering. The plant itself may start to lean. If underwatered long enough, leaves turn brown and crunchy and will start falling off.
Solution: Water your plant more often. Soil should be dry on the top inch or two, but don’t let it get dusty or bone dry between waterings.
While cannabis plants appreciate breezy environments to help reduce pest loads, too much wind can damage foliage. Too much airflow can cause leaves to lose water too quickly and curl.
Symptoms: Curled, “claw”-shaped leaves near the fan. Leaves further away from the fan are fine. Leaves may have small brown spots.
Solution: Move fan so it is further away from the plants, or so it is not directly aimed at them.
How to Check for and Remedy Common Nutrient Deficiencies
All nutrient deficiencies can potentially be caused by environmental stress, like underwatering or heat stress. If your plants have symptoms of other stressors and nutrient deficiency symptoms, focus on the stressors first and see if your nutrient deficiencies resolve before you address the deficiencies themselves.
Rare. Usually, a result of underwatering or a very dry environment, as cannabis plants do not need much boron.
Symptoms: Thick growth tips, spotting on new growth. May present as calcium deficiency, as cannabis needs boron to process calcium. Usually presents with underwatering symptoms as well.
Solution: Water plants more frequently. Make sure fertilizer is appropriate for cannabis plants, and make sur plant has enough nitrogen and phosphorus.
Calcium helps cannabis plants handle heat and adds structure to the plant. A deficiency is usually caused by a pH problem at the roots.
Symptoms: Speckled brown spots on leaves, usually appearing on new growth or heavily-light exposed leaves.
Solution: Check the growth medium pH to make sure it is within normal parameters and treat if it’s not. Otherwise, adjust fertilizer and possibly add a calcium-magnesium supplement. The leaves won’t heal, but new growth should look healthy once the problem is corrected.
Some strains of cannabis are prone to copper deficiencies when they’re flowering. This results in small, unhealthy buds. Usually caused by a pH problem at the roots.
Symptoms: Leaves turn dark with purple and blue undertones at the center, with light green or white edges. Most prominent in leaves that are well-lit.
Solution: Adjust the pH at the roots to the correct range.
Iron is vital to photosynthesis and enzyme function in cannabis plants. Usually, an iron deficiency is caused by a pH problem at the roots.
Symptoms: New growth appears bright yellow, without any green. Leaves sometimes fill in green over time, but sometimes the damage is too much and the foliage dies.
Solution: Check and fix pH levels in the growth medium.
Magnesium is essential to photosynthesis. Magnesium deficiencies can be caused by an overabundance of calcium or a pH imbalance in the growth medium.
Symptoms: Yellowing on the inside of lower and older leaves. These leaves may become crispy to the touch and usually fall off if left too long.
Solution: Test growth medium pH and fix if necessary. Otherwise, supplement magnesium and lower any calcium supplementation.
Manganese is necessary for respiration and photosynthesis in cannabis plants. Deficiencies are usually caused by pH imbalances at the roots or an overabundance of iron.
Symptoms: Yellowing of leaves from the base of the leaves outwards. Potential for mottled brown patches. Overall stunted growth.
Solution: Lower pH levels in the growth medium, and stop iron supplementation.
A rare deficiency outside of hydroponic systems. Molybdenum is naturally present in most mediums, so deficiencies are usually the result of pH imbalances at the roots.
Symptoms: Orange, red, or pink coloring moving from one part of the leaf and expanding. Yellowing of the leaves not affected by orange coloring.
Solution: Check the pH of growth medium and raise if necessary. Flush your watering system with pure water and then begin using of cannabis-friendly fertilizer made for your system.
Nitrogen is a key component of any plant. A lack of nitrogen can kill a plant from ineffective photosynthesis.
Symptoms: Pale, lime-colored leaves. Lower leaves yellow, wilt, and fall off.
Solution: Increase nitrogen supplementation – most fertilizers will help. Plants in the flowering stage need less nitrogen than plants growing foliage, so be cautious of over-supplementation.
Too much nitrogen prevents plants from flowering well, resulting in low yields and subpar buds. Nitrogen toxicity is usually caused by over-supplementation by the grower.
Symptoms: Dark green, shiny leaves, weak stems, claw-shaped leaves.
Solution: Stop supplementing nitrogen.
Phosphorus is closely linked to calcium in cannabis plants, and deficiencies often occur at the same time as calcium deficiencies. Usually caused by pH imbalances at the roots.
Symptoms: Lower leaves start to warp and get mottled spots, curl down, and darken. Stems turn red – however, this alone is not a sign of phosphorus deficiency.
Solution: Check growth medium pH and fix it if necessary.
Potassium helps regulate the transport of other nutrients in the plant. Potassium deficiencies are usually caused by pH imbalances.
Symptoms: Burnt edges and tips of leaves. Appears similar to nutrient burn, but leaves turn yellow at the edges as well.
Solution: Check pH balance at the roots and fix if necessary. Consider using tap water instead of RO water. Make sure it isn’t light burn, by checking all leaves for signs as opposed to the leaves nearest the lights.
Zinc helps regulate new growth upwards. A lack of zinc results in plants no longer growing upwards. Zinc deficiencies are usually caused by a pH imbalance at the roots.
Symptoms: New growth starts turning yellow between the veins, and leaves appear “banded.” The stalk stops growing quickly, resulting in new leaves being bunched together instead of spread evenly up and down a main stem. If flowering, the buds stop growing and may die.
Solution: Check pH at roots and correct if necessary.
How to Remedy Sick Cannabis Plants
Due to the fungus Botrytis cinereal, cannabis buds can sometimes rot from the inside out. Signs include yellowing, crunchy leaves and mushy buds. The buds turn black or purple and may appear fuzzy in a bad way.
PLEASE Be Aware: Bud rot is toxic to humans, and affected buds need to be disposed of immediately and with caution.
Solution: Increase air circulation, lower humidity, and remove affected buds immediately. Consider removing foliage from plants that are very bushy, to help keep buds from rotting.
Leaf Septoria (Yellow Leaf Spot)
Leaf Septoria is caused by a variety of plant bacteria and fungi in warm, wet weather. It looks like yellow circles with hazy edges that spread over time. There is often a small black speck, a spore, in the center of the circle.
Solution: Remove all affected leaves carefully. Sanitize tools used to prevent spreading again in the future. Increase airflow around the plants, and remove leave litter. Spray with Neem Oil – if a fungus is causing the problem, it will help.
Caused by overwatering and the growth of bad bacteria, root rot results in slimy, dark, brown roots. They often start twisting together. Root rot is most common in heavily-overwatered plants or in hydroponic systems. Root rot results in drooping plants.
Solution: Stop overwatering, increase water oxygenation in hydroponics systems, and introduce healthy bacteria to the water through a commercial product like Hydroguard.
White Powdery Mold
This mold appears as dusty white patches on the leaves or stems of your cannabis plants. It looks like powder or dust and spreads easily. If caught early, it is easily treatable, but if left alone it can ruin an entire crop. It is encouraged by high humidity and still air.
Solution: Lower your garden’s humidity and increase airflow and ventilation. Spray your plants with water and wipe them down, then spray again with Neem Oil or Spinosad.
Common Types of Cannabis Pests
Aphids are green bugs that live underneath leaves and suck the juice out of your plant. They can kill a plant easily if it gets infested, and can spread quickly. They also secrete honeydew that can attract sooty mold.
Solution: Introduce ladybugs and other aphid predators to your garden to eat the aphids. Spray the plant with insecticidal soap or Neem Oil.
These bugs live on the stems and leaves of your plant. They consume nutrients from the sap, weakening your crop, and do not move once they have attached to the plant.
Solution: Use a power sprayer to knock off the barnacles, and then spray with Neem Oil, Spinosad, or insecticidal soap.
Contrary to their name, broad mites are so tiny that they can’t be seen. They cause droopy, twisted, blistered, and glossy leaves. The symptoms are similar to heat stress and root problems. The parts infested look worse than the rest of the plant.
Solution: Remove affected parts of the plant. Spray with Spinosad, Neem Oil, or insecticidal soap.
Caterpillars and Inchworms
These pests leave smooth-edged holes in your leaves. They also leave leaf pellets on your leaves. A large number can devastate your crop.
Solution: Spray your plants with BT Spray, a safe, biological insecticide made with the bacteria bacillus thuringiensis, which kills caterpillars and not other, beneficial bugs.
Fungus gnats look like tiny fruit flies. Their larva live in wet soil and may eat rotting roots. They usually appear when plants are overwatered, or when the soil stays wet too long.
Solution: Let the soil of your plants dry out down an inch or two between waterings and they should go away on their own. You can also wrap the pots of the plants in plastic up to the stem and suffocate them out.
Grasshoppers, crickets, and locusts all eat cannabis plants more or less at random. They eat the edges and centers of leaves and can eat through stems, killing the entire plant.
Solution: Use Neem Oil, Spinosad, or insecticidal soap to kill any grasshoppers that eat your plants. You can also cover your rows with floating row covers because these bugs are too big to fit through the mesh.
These bugs can jump from plant to plant, as well as fly, so they spread easily. They suck the nutrients out of cannabis plants and leave behind brown or yellow spots that can kill the leaf. There are thousands of varieties that all look different.
Solution: Keep an eye on your plants for spots, especially in dry times. S[ray plants with insecticidal soap, Spinosad, or Neem Oil to remove the problem.
Leaf miners actually live inside the leaves of your plant. They leave squiggly lines in the leaves, showing where they have “mined” through, eating the nutrients that help your plant thrive. They are the larvae of many species that all do the same kind of damage.
Solution: Remove affected leaves so the larva cannot spread to other leaves or mature into the adult bug. Spray with Spinosad or BT Spray to kill any adults.
Mealybugs are white hairy bugs. They leave behind white powdery patches that look like white powdery mildew and secrete honeydew that can attract ants and sooty mold.
Solution: Knock off as many mealybugs as you can with water or other methods, then regularly apply Neem Oil, Spinosad, or insecticidal soap until you are sure they are gone.
Slugs and Snails
Slugs and snails eat leaves, buds, and plants wholesale. They also leave trails of slime on the plants they have attacked. The damaged areas have “scalloped” edged.
Solution: Encourage the presence of slug and snail predators in your garden, like toads and beetles. Surround your plant with diatomaceous earth or eggshells, or wrap the base of the plant in a plastic bottle cloche.
Spider mites create dusty webbing at the intersection of leaves and stems, and on the underside of leaves. They also create mottled yellow spots on the leaves. They are almost invisible, but they colonize quickly in areas without air movement.
Solution: Get some source of airflow for your plants, rinse with water, and then spray with Neem Oil, Spinosad, or insecticidal soap.
Stink bugs primarily eat the flowers and buds of cannabis plants, so they are a danger to your crop. They are also bad neighbors for people. The first sign of stink bug infestations is a patch of eggs underneath a leaf – they are relatively large and obvious, for insect eggs.
Solution: Get rid of any plant litter in the area in which adult stink bugs may hide. Use Neem Oil, Spinosad, or insecticidal soap to wipe off the eggs and larva. Avoid squishing the bugs or you will be covered in their awful smell.
These bugs are tiny and fast-moving insects that suck out the nutrients from your cannabis plants’ leaves. The larva looks like tiny, still worms. Thrips leave shiny, slimy spots on the leaves where they bit the plant. This can kill the leaves and is unsightly.
Solution: Spinosad, Neem Oil, and insecticidal soap can all clear your plant of thrips, but the leaves likely won’t recover aesthetically.
Whiteflies look like tiny white moths flying around your plants. They live on the underside of the leaves and suck nutrients from the plant. This can cause white spots on the leaves. However, the bugs are noticeable before the leaf damage, usually. Their eggs are almost impossible to get off the plant.
Solution: Spray the plants with Neem Oil, Spinosad, or insecticidal soap. Just be cautious to wash any of these off your buds.
Cannabis plants, as with any other type of plant, require a steadfast maintenance routine to ensure that they yield a healthy harvest.