When trying to grow your own cannabis, each marijuana leaf can tell a story about the current health of the plant.
Underlying marijuana plant problems often show up in very obvious ways. Yellow leaves on a cannabis plant can indicate a nutrient deficiency, for instance. Or, you may see cannabis low humidity symptoms, such as slow growth in young plants.
Luckily, all of these problems can be fixed, as long as you catch them early enough! Cannabis may not be as easy to grow as industrial hemp, but it’s still not nearly as picky as other plants.
To help you deduce exactly what your marijuana plant needs, you can use the following marijuana leaf symptoms to diagnose problems early on and hopefully fix them to have a great harvest.
Marijuana Leaf and Stem Structures Look Limp or Wilted
Droopy leaves usually relate to not giving the cannabis plant the right amount of water.
Your first step is to rule out underwatering. If you’re underwatering your plant, this is one of the easier problems to fix. But if you wait too long, you can easily stunt its growth or kill off your entire plant. An underwatered plant will have dry soil. All you have to do to check the soil dampness is poke your finger into the soil about an inch deep – just enough to creep past your first knuckle. If the soil feels light, airy, and as dry as desert sand, then you haven’t been giving the plant enough water.
Ideally, you will water the plant every 2-3 days. If your soil gets dry much more consistently than that, you should use a richer soil that absorbs more water. You may also be using too small of a pot, which causes the roots to drink up all available water faster than usual.
On the other hand, if you poke your finger in the soil and feel that it’s damp, you may have overwatered your plant. Overwatering is a serious problem that should be addressed immediately. If you don’t address it, you could starve your plant of oxygen and cause root rot. Your first step is to commit to not watering the plant for at least two days. Also, check the current soil water levels and how the plant is potted in general. Make sure the bottom has ample drainage. If you have too little drainage, consider drilling more holes into the pot, repotting the plant with a gravel/soil mix on the bottom, or downsizing the pot in general.
Yellow Leaves on Cannabis Plant or Other Discoloration
Yellow leaves on your cannabis plant can indicate a broad range of problems with your marijuana plant, most of them related to nutrition.
First, you want to rule out overwatering or underwatering issues as described above. Either problem can lead to plant death, which causes yellow leaves and dropped leaves, especially if the plant has contracted root rot.
If you don’t think you have water-related issues, here are a few symptoms and what they can possibly indicate:
- Yellow or brown tips – Nutrient burn, which comes from giving the plant too many nutrients or nutrients in too high of a concentration.
- Top inner leaves turning yellow and white – Iron deficiency.
- Lower leaves with oldest growth turn yellow between veins – Magnesium deficiency.
- Leaves turning yellow between veins with brown spots – Manganese deficiency.
- Lower leaves yellowing and falling off – Nitrogen deficiency.
- Yellowing and dark splotches appear on leaves that drop off – Phosphorous. deficiency
- Yellow along smaller veins with brown or yellow edges – Potassium deficiency.
- Lower leaves turning yellow at base, spreading to tips – Sulfur deficiency.
- Top leaves turning greenish yellow – Zinc deficiency.
- Upper leaves dark with tips and edges turning yellow – Copper deficiency.
- Yellowing stems that feel hollow, brown spots – Calcium deficiency.
- Newer growth is thick and unusual looking, with yellowing and brown spots – Boron deficiency.
Because many of these symptoms appear similar, you may find benefits in keeping a log of your plant’s nutritional intake. You can also experiment with supplementing just one plant exhibiting these problems with a nutrient, while leaving a control plant alone to see if the problem clears up.
Also be aware that marijuana leaf discoloration can come from plants that burnt by grow lights or sunlight.
Curled Cannabis Leaves
Curling downward can be the result of underwatering. Curling upward can be caused by heat stress. Marijuana leaves that are curled away from the plant can indicate windburn, usually as a result of being too close to a nearby fan.
Another condition can cause a particular type of curling called “nitrogen toxicity”. Nitrogen toxicity occurs when too much nitrogen is present in the plant or the soil. You will see dark green marijuana leaf colourations with the tips of the leaves curled aggressively downward.
Cannabis Low Humidity Symptoms
In addition to watered soil, cannabis plants prefer a mildly humid environment. This humidity allows the plant to absorb water through stoma, microscopic holes found underneath the marijuana leaf.
For young plants, the ideal relative humidity is 70%. This level ensures that the plant can absorb plenty of water without having to rely upon its root system. Also, if the humidity is too low, the plant may shut out its stomata (the plural of stoma) and cause growth to slow to a crawl. Extremely slow plant growth is one of the most common cannabis low humidity symptoms.
On the other hand, if the humidity is left too high, the plant will absorb less water through its roots, which leads to fewer nutrients in the plant. After the young plant’s growth spurt, reduce the relative humidity in the room by 5% each week to around 40% for a maturing plant getting ready to bud.
Bug Bites and Other Marijuana Plant Problems
Bugs leave telltale signs on cannabis leaves and in the soil. You may see tiny bites on your plant or unusual “bubbles” throughout the leaves. The leaves may also curl and turn glossy or waxy, indicating that aphids or mites may be sucking the leaves dry.
If you are having cannabis plant issues that can’t be diagnosed by any of the above tips, look for signs of infestation on your plant or in your soil. Check your water levels, check your soil pH, adjust temperature and humidity, and keep a close eye out for any other emerging symptoms.