If you’ve ever had to ask yourself “Why are my weed leaves turning brown?” you know the struggle. When you’re growing cannabis, nothing is more disheartening than seeing young plants lose their healthy appearance. For most DIY or home-growers, growing weed represents a serious investment of time and resources. Often, it’s a labor of love. So when leaves start to curl and turn brown, and growth starts to slow, panic can set in.
The good news is that browning is kind of an early warning sign for problems with your grow. If you can diagnose the problem correctly and take the right steps quickly, you have every chance of saving your plants.
This guide lays out several of the most likely causes of weed leaves turning brown. It also provides some immediate steps you can take to reverse course and return your plants to a healthy grow cycle.
Why Are My Weed Leaves Turning Brown?
Whatever the cause, the answer to “why are my weed leaves turning brown?” is almost always an imbalance in the nutrients your plants need to grow up healthy.
The tricky part is identifying what exactly that imbalance is. Because browning is a common symptom of many grow problems, there’s some trial and error involved in figuring out what exactly needs to change.
1. Light Burn or Heat Stress
Before checking in on the soil you’re using to grow your plants, make sure no environmental factors are causing your weed leaves to brown.
Check your lights and the temperature of your growing situation. Whether you’re an indoor or outdoor grower, light burn can be one reason why you’re asking yourself, why are my weed leaves turning brown?
Although cannabis grows best in sunny climates, there are limits to how much heat and light it can take. If there’s too much light, stress will appear on the serrated edges of the leaves. You’ll see curling, yellowing, and browning.
The solution, however, is rather easy. Just find a way to lower the temperature in the grow area. Or, you could add fans to improve air circulation. Even more simply, just move your plants further away from the lights or heat source. You can even try reducing the number of lights.
2. Nutrient Burn
Many first-time growers encounter problems with nutrient burn. The issue arises especially in hydro setups, where growers prepare a liquid nutrient solution for their plants.
Inexperienced growers sometimes think more is better. More light, more nutrients, more bud, right? Actually, more is not always better, and over-saturating your cannabis plants with nutrients is a common way to end up with brown weed leaves.
You can diagnose nutrient burn if your weed leaves are turning brown at the tips first. If the browning starts to spread to the whole leaf, or the tips start to curl, it’s time to move quickly!
Flush your system with plain water. And be patient. Your plants will need some time to recover. When you go back to adding nutrients, start with small amounts and build up. Use recommendations on nutrient solutions you buy as a maximum amount. You probably need much less.
3. Phosphorous or Potassium Deficiency
For soil growers, the most likely response to the issue of why are my weed leaves turning brown is a problem with the macro-nutrient balance in the soil.
When you buy soil from a store, the package is labeled with three super-important numbers. These numbers are called PKN, and they represent the amounts of potassium (K), phosphorous (P), and nitrogen (N) in the soil.
While it’s totally possible that you could be facing a problem with too much potassium or phosphorous, you’re far more likely to be facing a problem with too little, or a deficiency.
Symptoms appear in the form of browning and yellowing on the tips and margins of leaves. The whole plant will soon become brittle, and eventually, begin to die.
If the issue is specifically phosphorous, you’ll notice slow growing, stunted plants, and maybe even some purple coloring. Leaves will go brown, curl under, and die. Tiny buds on flowering weed plants are another sign of low P.
The solution is to slowly increase the levels of P and K in your soil. You can also flush the soil to remove or dilute salt buildups that can trigger P and K deficiency. Cold weather may also be a cause for outdoor growers.
4. Nitrogen Toxicity
Remember that other number on the PKN scale on your cannabis soil mix? Nitrogen is another macro-ingredient that can be responsible for turning weed leaves brown.
Nitrogen toxicity, however, is a bit harder to diagnose. And that’s because its symptoms look like deficiencies. So you may think the reason why are my weed leaves turning brown is that something is lacking. When in reality, you have too much nitrogen.
Fortunately, there is one tell-tale sign of a nitrogen-related problem. The leaves will turn yellow and begin to curl and brown. But the rest of the plant will remain a dark green.
There’s a weird curling or cupping thing that happens to weed plants with too much nitrogen. This symptom is called “The Claw”. Many growers mistake this as a sign for over-watering. Different strains get “The Claw” differently. Some will bend at 90 degrees, some will curl, turn yellow-brown, and fall off.
5. Root Rot
Sometimes, problems with the leaves are just the visual manifestations of problems you can’t see. Root rot is a plague for cannabis growers and can be a major cause of brown weed leaves.
Root rot begins when you have too much water and not enough oxygen around your roots. Rotting roots are easy to tell. They’re brown and smell like rotting. Instead, they should be white to cream-colored.
Plants with root rot can’t supply the nutrients needed for the plant to grow. Soon, leaves will turn yellow, then brown, then start dying rapidly. You can tell the problem is with the roots because the plants will drink less water.
Root rot is irreversible. However, the plant can grow new roots. It can be difficult to git rid of root rot, so most people scrap the plant and start over.
The Final Hit: Why Are My Weed Leaves Turning Brown?
In this guide, we’ve looked at five of the most likely culprits causing your beautiful weed leaves to turn brown. Here’s a quick summary.
- Environmental issues like excess light and heat can burn plants and turn leaves brown.
- Deficiencies or toxic buildups of macro-nutrients in the soil can turn leaves brown and are harder to diagnose.
- Root rot is basically a death sentence for your plant and will cause leaves to turn brown and die rapidly.
Luckily, generations of cannabis cultivators have figured out how to tell what is actually causing weed leaves to turn brown, and also the correct steps to fix it.