12 Common Cannabis Leaf Problems and How to Fix Them

Julien Bissonnette | June 03, 2022

Canada Grow Supplies offers some of the best hydroponic supplies in Canada to ensure that your plants and new growth are healthy and thriving. If this is your first time foraying into the world of growing, you will need a guide, a gentle nudge in the direction of a healthy garden, and avoid mishaps as 82.3% of growers experience cannabis leaf problems- here are the top twelve of them. 

The marijuana plant is a weed that is very alike to other garden favourites such as the leafy green urticae (stinging nettle) and though it is a weed, it can require a great deal of care as with our other garden favourites. Let’s look at the topmost persistent problems facing growers today.

 

Frequent Problem % of Growers Facing Problem
Spider Mites 35.85%

 

Heat Stress

 

33.96%

 

Powdery Mildew

 

28.30%

 

Under Watering & Overwatering

 

26.43%

 

Nitrogen Toxicity & Deficiency

 

24.53%

 

Light Burn

 

20.75%

 

Aphids

 

18.87%

 

Bud Rot

 

16.98%

 

Nutrient Burn

 

13.2%

 

Whether you are interested in harvesting for gummies production, hemp crafting, or for cannabis strains, where should you start in the process? With cannabis seeds? First, take a look at these 12 frequent cannabis plants grower problems, and how to fix them so you are prepared to tend to your garden from the outset.

12 Common Cannabis Leaf Problems


1. Spidermites

Spidermites (tetranychus), the bane of any grower’s existence, well next to the pest thrips that is. Weed plants can get this pest more commonly than they get others so when spider mites arrive it is very exhausting and often damaging to the cannabis plants to properly deal with them. The trick is to catch these fuzzy red bugs early, to do so, monitor your plants and comb through them every couple days in search of signs of spider mite or other pests. Check on the underside of the buds especially as they like to hide there. Use a magnifying glass to enhance your vision of them, they are tiny spider looking mites that crawl on and will eat at your marijuana leaf.

 

One way to ensure you catch the early signs of these bugs is by looking out for small light-coloured spots on the cannabis leaf, these dots will be very close together and small. You may even see webs- very similar to those of spider’s that will cover the leaves. This is usually only in the case of a plant that has not been taken care of and will likely be too late to then save. However, as stressed, check out for mites constantly and then you can address problems early on.

 

A very organic and adorable option to deal with the pest is to employ ladybugs! They are very cheap to buy at your local gardening store and will gobble up the mites in a snap! This is important as the bugs can reproduce at an alarming rate, so make sure to kill every single last one of them in order to create a barrier and avoid a reemergence.

 

 

2. Heat Stress 

Cannabis buds in their gentle little vegetative stage can only handle so much heat, though let us not forget that the grow light, one of the essential pieces of equipment, is so important for growing indoors and providing enough light. Plants need artificial sunlight but can get too much heat. One must be careful that the heat emitted by these lights can be handled by the plants. Heat stress is caused by harm from light sources (sunlight or artificial). This is a good reason to try LED lights, they emit less heat and can still provide the artificial sunlight your plant so needs. Grow lights are particularly important in making a space to nurture new growth.

 

3. Powdery Mildew

Powdery mildew Infestation is a fungal malady and leaves its’ branching filaments or hyphae, which is speckled in appearance, all over your buds. White powdery mildew (golovinomyces)- akin to the similarly named downy mildew, erysiphales, or trichoderma- appears as mildew like white spots, a very common type of fungi that eats at your plant while busily multiplying and spreading. Cannabis growers encounter this often as a result of too high a humidity, to avoid this in your grow room try the Hyper Fan Digital Mixed Flow Fan to keep the air flowing and to lower the humidity. These powdery white dots, and other nuisances like it such as septoria, can also be misted away with a mildew eradicating spray or a fungicide!

 

4. Under Watering

Like all plants, marijuana will not deal well with the wrong amount of water, whether that be too much or too little. But not to worry, if caught soon enough this problem has an easy solution and a quick remedy. With under watering you will see your plants leaves begin to droop, simply water the plant when you notice this and the buds will pop right back up in 30 minutes or so! Be careful not to drench it though, then you will begin the cycle of under/over watering all again. If the leaf seems dry and not vivid and lush, this is a good sign that the plant needs some rejuvenation with water. 

If you are working with hydroponics then a good pump is recommended to keep the water moving at the appropriate amounts. We stand by our Active Aqua’s pumps submersible pumps which are engineered explicitly for hydroponic systems, they are BPA free and are built to last with high quality components. 

 

5. Over Watering

 

 

If you have overwatered too liberally it can be deadly and can cause root rot, you will notice this is occurring when the leaves begin to turn yellow and the growth slows down considerably. It is clear when you have been over-watering a plant as it causes the stems and leaves to become turgid and the leaves to curl inward due to this rigidity. As growth has diminished it is time to dry out the plant as much as you can, place it near a dryer and do not water it again for many days until the soil is dry and not still wet down at the roots. As you water it less frequently you can put your finger in an inch deep in the soil and test that it is dry, then you know it is time to re-water.


 

 

If you are in need of a fan get the Spider Farmer® SF2000 with LED Grow Light, Tent, and Fan- it includes all of the necessary elements in order to grow successfully- especially if you have over-watered and looking for drying and proper air circulation. Or if you are doing aeroponics you can purchase the Flood Valve W / Fast Drainage Port Kit to quickly recirculate and control the amount of water.


 

 

 

 

 

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6. Nitrogen Toxicity and Deficiency

Cannabis plants are liable to get too little or too much of nitrogen in the soil. If you have nutrient deficiencies it is best to use foliar spray to help if you do not have the healthiest soil and to replenish it. Cannabis plants survive on nitrogen (also phosphorus and potassium), thus if they have too much or too little things go awry. The leaves will die after they turn electric yellow if the flower requires more nitrogen, what you do is simply fix the pH by adding nutrients that is high in nitrogen into the soil. Be careful as buds, close to harvesting time, often turn yellow as the plants last growth faze leeches nitrogen from the system. If this is the case, do not bother adding more nutrients to your soil, it is good to go!

 

If you have too much nitrogen you can tell this by the claw shape that the leaf will take on, curling inwards and downwards and becoming a dark green colour. Be careful of this, to remedy it lessen the amount of nitrogen you mix into the feedings.

 

7. Light Burn

  

If as a grower you have placed your plants too close to a light source they can actually bake or at the very least turn a blue-green cannabis bud yellow-brown. To prevent this, watch out for yellow leaves next to lights and move your plants away that are closest to the grow lights, or switch them up with other plants. It is paramount to stop the yellow and brown spots from spreading to other parts of the plant which happens with light burn. 

If you catch this issue in time, you will save yourself a whole load of trouble. Simply raise your lights anywhere from 5 inches to 1 foot. Your light position will vary dependent on what flowering stage you are at or whether it is a new growth or not determines the strength required for the lights. There is helpful information in the manual that accompanies your lights that will aid you in determining the distance required for that specific light.

 

 

 

 

8. Aphids

 

 Aphids are very similar to whiteflies however mimic spider mites and in that they cleave to the bottom of the fan leaves; the underside of the cannabis plant will be covered with these little green leaf miners that have longish legs and a trapezoid body, they are pretty minute so using a magnifying glass to view them is preferable. These planthoppers will crawl around and make a drink of the weed by sucking the nutrients and water from the leaves. This causes the leaves to wilt an eventually die. This pest is the absolute worst, similar to a vampire.

 

The solution is the same as with spider mites and pythium (fungus gnats), use aphids! These bugs are hard working at eating predatory pests, it is as simple as adding the ladybugs to your plants and they will figure out how to do the rest. But be sure to use this remedy quickly, otherwise the aphids will create an inhospitable environment for the lady bugs to even create a solution. 

 

9. Bud Rot

Bud rot, or Botrytis, is one of the worst leaf mold and root problems that a cannabis plant can have. It is similar to mildew in that it has spores and is caused by high humidity levels (a minimal air flow situation) or overwatering. It basically is the rotting of your cannabis flower, moldy weed, but it can be difficult to spot even though the leaves actually do have mold. This is because it is an interior problem first, spreading to the outside and later turning it moldy and brown, destroying the entire bud.

 

It can be a fairly easy fix to stop bud rot in its’ tracks, one great way is to invest in a fan such as the Active Air 16″ Oscillating Wall Fan. This is crucial to lowering the humidity in your grow room so that the weed can grow mold free with good air flow. Another step is removing all of the infected buds- this may be difficult however many of the cannabis buds are harmed in the middle- so break apart your weed to check the centre. It can seem like a big waste but it is pointless to use this weed, it will only make you ill.

 

10. Nutrient Burn

  

Your plant may yellow from over-watering, being under-watered, and something called nutrient burn. This is a frequent symptom that plagues newbies to a more adept grower alike and comes from an over-nurturing instinct to feed plants beyond their limited capacities. So a good rule of thumb is to remember when feeding ones plant that restraint is preferred. Remember the common fertilizer N-P-K is made of nitrogen, phosphorus, and potassium- all robust elements to be used with measure.

Essentially you burn your plants when providing them with too strong nutrients, or feeding them too much nutrient-rich mix, or perhaps when doing these things too frequently. You can spot nutrient burn when your plants’ leafy edges are browning and quite literally look scorched and brittle, the growth is substantially slowed at this point. 

To avoid a crispy appearance and poor growth rate, note that the pattern of the burn occurs from the tips of the plant, so be sure to check if the colour of your tips are changing. If you notice something awry abstain from feeding them the nutrients for a week or even two before you continue. It is best to wait for the plant to flush out the nutrients and return to balance again.

 

 

11. Thrips

 

Thrips are the fear of any expert grower and are sometimes a houseplant inevitable eventuality, these are not cannabis-specific and infest other greenery. If you get them, do not fear, here are step-by-step ways to deal with this dark sliver of a predatory pest that eats the trichome, or hairs and vegetative matter of your leaf.

 

First, remove any of the infected plants leaves or stems. This may seem drastic, but it is necessary to separate the pest-free from the infected areas. They will spread similar to lice in school yards and reproduce uncontrollably. It is best to try removing bugs with blasts of water on the infected area, but be sure not to be too rough and break or damage your plant when doing so.

 

Next, gently apply neem oil, a pungent natural oil spray that will scare any predator off (it is ingestible and tastes as horrible as it smells) or you can use insecticides soap and apply it carefully with a silicone cloth to the leaf tips. Be stingy and careful when applying to new growth or plants in their flowering stage as these are powerful oils and soaps. Or anoint hydrogen peroxide on the plant, also do this sparingly.

 

Another tell-tale tactic is to allow for other pests such as mites to eat the invasive critters, sometimes this is preferable as the mites are easier to get rid of afterwards and they will kill the unyielding bugs. It is a risky gamble, but they will hold you in a death grip otherwise, think of this tactic as organic and working with the thrip’s natural predators!

 

Be sure to take away from your experience that you must tirelessly work to prevent future infestations by constantly checking your weed for outbreaks of these common pests so that you can ‘nip them in the bud’. It is best to separate healthy plants entirely in a grow tent, for instance order the all star Mars Hydro Tent Kit replete with LED grow lights, hanger kits, a grow tent with an inline duct fan, carbon filter, grow bags, and a humidity thermometer.

 

 

 

 

 

12. Incorrect pH Range

Having the incorrect pH levels causes the plants to suffer under undue stress while trying to absorb the nutrients and water that you give it. It is an incredibly typical situation for growers to struggle ensuring that cannabis plants are healthy and keeping the correct pH range; having a pH tester is necessary for plant success. 

What essentially happens is when the pH levels are off the plant goes into shock and stops absorbing nutrients any longer until the homeostasis is returned. This is generally the first go to issue that growers have with their marijuana plants, even before the culprit nutrient deficiency- which would be a disaster to assume was the issue in this case as your plants are already weighed down and would exhibit more symptoms if you overfed them incorrectly. Use a pH meter and add nutrients accordingly. 

 

Other Leafy Troubles

 

There are many vegetative stages that a plant can go through, and (unfortunately) a bevy of deficits to be had that we haven’t covered above. One such is chlorosis, which is when a plant has insufficient chlorophyll. There is a multitude of other nutrient deficiencies like phosphorus deficiency, which means that there are inadequate amounts of that particular nutrients, more deficits include manganese deficiency, magnesium deficiency, potassium deficiency, copper deficiency, sulfur deficiency, zinc deficiency, iron deficiency, boron deficiency, calcium deficiency, and nitrogen deficiency. 

For these problems use the appropriate materials in your soil and purchase a grow tent while ensuring you have adequate pumps for hydroponics or aeroponics, and fans for air circulation. Keep a vigilant eye out for pests and watch how much you feed and water your marijuana plant!

 

FAQ’s

How can I fix it when I have watered too much?

Water less frequently and let your plant dry out, place it next to a dryer and let it get good air flow. If you are in need of a fan and a grow kit the Spider Farmer® SF2000 with LED Grow Light, Tent, and its’ Fan includes all of the necessary elements in order to nurture new growth successfully, especially if you have over-watered and are instilling a new proper air circulation regime.

 

What do I do with thrips?

1. First, remove any of the infested pot leaves or stems.

2. Next, gently apply neem oil or hydrogen peroxide carefully to the foliage

3. Keep healthy plants completely separate from the unhealthy

4. Constantly check your flowers for outbreaks of these common pests

 

How to avoid nutrient burn?

Simply put, do not overfeed your plant any of the various nutrients. In the same way that a plant can be overwatered, it can be overfed. It is best to restrain when adding nutrients into your plant until you see how they react to what you have added before topping up more. Your flower can have too much nutrients, otherwise it will stop growing properly and will yellow in colour. Fight your inner over nurturing instinct and abstain from adding abundantly. 

 

 

What’s best for light burn?

If your plants leaves are starting to yellow, it could be because of watering, not watering, enough, nutrient burn, and also light burn (check this first). Starting by removing your plant away from the direct light source will be the quickest way to reverse your plants frying. There are a couple of ways to correct this, one is to invest in LED’s such as the GE LED Arize Factor ML900 which does not get hot over time and will not singe your plants. You can also switch your plants around that are closest to the lights to disperse the ‘cooking’ effect. For your growing lights there is helpful information in the manual that accompanies each kit and will aid you in determining the distance away from the plant required for that specific light.