by Nebula Haze
Leaves have burnt tips, yellow tips, brown edges… These are some of the most common symptoms growers see on their cannabis plants. It can be hard to identify the cause because a lot of different things can cause similar symptoms.
Today I’ll break down all the reasons you might see brown tips or yellow leaf edges. Get to the root of the problem and get back to green healthy leaves!
Nutrient burn is a common cause of burnt leaf tips, but not the only one!
1.) Nutrient Burn
There are a few possible causes for discolored leaf tips, but one of the most common is nutrient burn.
This happens when you are giving cannabis plant too high levels of nutrients. Usually, the first signs of cannabis nutrient burn are yellow or brown tips on leaves after increasing the overall amount of nutrients. As time goes on, the brown continues inward and the tips start curling up. The tips will be dry and easily break off with any pressure.
Nutrient burn is brown and appears on the tips of leaves and causes ends to curl up
2.) Light Burn
Plants can get light burn (sort of like a sunburn) even if the temperature is completely under control. The symptoms are usually concentrated close to the grow lights.
A lot of growers don’t realize that light stress (lights being too close) can cause yellow tips. This symptom is often mistaken for nutrient burn. You can tell the difference because the yellow tips on appear on leaves close to the light. With nutrient burn, the tips are usually brown and appear all over the plant.
Yellow tips from the grow light being too close (light stress)
Light burn can cause the leaves closest to the light to turn yellow or brown around the edges
3.) PH or Nutrient Problem
Certain nutrient deficiencies are often mistaken for nutrient burn.
Here are some common nutrient deficiencies that can also cause burnt or yellow leaf tips and edges. Nearly all of these examples were caused by Incorrect pH (the #1 cause of nutrient deficiencies).
A potassium deficiency causes the edges of leaves to appear burned
A potassium deficiency can express itself in a few different ways
A copper deficiency causes dark leaves with yellow edges
A magnesium deficiency can also discolor the leaf edges
The best way to prevent nutrient deficiencies is to make sure you’re giving your plants the right type of nutrients and pH’ing the water to the proper level depending on your growing medium. But that doesn’t mean more is better. It’s important not to overload your plants with too high levels of nutrients.
Too Much Nitrogen (Nitrogen Toxicity) causes dark green leaves that often feel dry and crispy and get discolored edges
What about Calcium deficiencies?
It used to be that a lot of growers thought brown tips were caused by a Calcium deficiency. However, we’ve since learned that’s incorrect. Here is what a real Calcium deficiency looks like.
Calcium deficiencies don’t cause brown tips. This is a calcium deficiency.
Another example of a calcium deficiency (no brown tips). It mostly affects the middle of leaves.
4.) Heat Stress
Even if your grow light is a good distance away from your cannabis plants, they can still get stressed out by too much heat. Cannabis plants generally prefer temperatures under 85°F / 30°C, though some strains are more sensitive to heat (shorter, bushier strains are often more sensitive to heat than the longer, lankier strains).
Most plants are fine with a few hot days, but if it’s hot every day for weeks, your plants can really start to suffer. Most marijuana plants can handle a small heat spell, but they don’t want to live in a desert! Learn 5 secrets to controlling heat in the grow room.
Heat Stress can burn leaf edges
The following plant experienced 100°F (38°C) temperatures for several days during a heat wave. Burnt leaf tips doesn’t even begin to describe what happened to this poor plant.
An extreme case of heat stress
5.) Root Problems, Root Rot or Bad Watering Practices
Chronic overwatering can sometimes cause unusual deficiencies even if the pH is spot on, like this plant grown in muddy soil. The biggest sign that these symptoms are caused by overwatering and not pH (or something else) is that the plant is always droopy.
Another example of a deficiency that’s actually caused by overwatering (notice how this seedling is also droopy)
6.) Bugs or Pests
If you ever experience a big infestation, bugs and pests can cause a surprising number of symptoms including burnt leaf tips or edges.
Fungus Gnats are one of the most common. They look like tiny flies buzzing around your topsoil. Although a few fungus gnats won’t really hurt your plants, a ton of them will damage the roots, causing symptoms similar to other types of root problems. This can include brown or burnt leaf edges.
A bad fungus gnat infestation can cause a variety of symptoms
Leaves with brown tips, burnt tips, and yellow tips can be hard to diagnose because so many problems can cause similar symptoms. Once you know the cause it’s easy to fix, but if you don’t know it’s impossible! I hope this article helped you figure out what’s causing your symptoms so you can get back to growing.
You’ve got this!
You may enjoy the following articles…
- Why Are Leaves Dry or Crispy?
- The Solution to Yellow Leaves
- What Causes Red Stems?
- Fix Curling or Clawing Leaves (“The Claw”)