Why are my leaves turning yellow / brown / red / spotted?

Sometimes your yields don’t turn out the way you want them. It is possible that your leaves curl up or down or turn yellow, brown, red or even get spots. This problem can have multiple causes and you want your plants to be happy. Hopefully, I can explain to you what you can do to get your cannabis in perfect health and solve the problems you are having.

What is wrong with my plant?

First of all, you need to figure out what is wrong with your plant. Are your leaves having a different color than is usual or are they curling up or down? We are going to figure out what is wrong and what we can do about it. Usually, you can follow three steps to determine what is wrong with your cannabis plant. Only proceed to the next step if you are sure that you can exclude the previous step. If you are sure none of these three possibilities is the one you are encountering, then look to the other options that we have summed up at the end.

The top 3 causes of plant problems:

1. pH imbalance
2. Nutrient Deficiency
3. Watering problem

Other possible causes:

• Light burn;
• Heat stress / cold shock;
• Not enough light;
• Bugs or pests;
• Bud Rot.

#1 Problem: pH Imbalance

The pH of the growth medium where your plants are in is very important to nutrient uptake. For hydroponic systems, the perfect pH range is 5.5 – 6.1, so make sure you test your water. Marijuana soil has a perfect pH range of 6.3 – 6.8 to optimize nutrient uptake. If your medium is outside its perfect range, your leaves will turn yellow because some nutrients won’t be able to be taken up by your plant. Check out the image below to see which nutrients are being taken up in which range.

You can solve your pH imbalance in various ways. In all cases, you will need a pH testing device, such as a digital pH Pen, pH test strips or pH drops. If you can’t test your pH, you don’t know how to correct it if necessary. If you think there is a pH imbalance, test the water that runs out of your soil or the water in your reservoir (when using a Hydroponics system). You can correct the imbalance by using chemicals that correct your pH up- or downwards. It is a fairly common problem that your imbalance is caused by using too many nutrients. These nutrients cause your soil or water to have too much salt. Fixing a pH imbalance is almost never fixed by adding more nutrients and only cause your problems to become only bigger. Use the pH adjustments after you have added the nutrients so you can make sure that the pH balance is right of your nutrient mix and not just the plain water you’re adding.

#2 Problem: Nutrient Deficiency

Are you sure that your pH is correct? Only if the answer is yes, you can start looking at the nutrients your plant is getting. Take a look at the image below to see what could have been the nutrient that your plant is lacking. If you think a nutrient deficiency is what causes your plant to behave differently than usual, make sure you get the right nutrients for your plants.

#3 Problem: Watering Problem

This problem is easy to fix. You can either give your plant too much or too little. If you are giving your plant too much water, you are watering it too often. As long as your container has holes at the bottom of your pot, the amount of water you add at once doesn’t matter. There are two easy steps you can remember to water your plants:

1. Make sure that the soil is so dry that you can feel dry soil a knuckle deep. Check this by sticking your knuckle in the dirt and feel it.
2. Add water and nutrients until the water leaks out of your drainage (the holes at the bottom of the pot). After you have watered it, return to step one and repeat.

Other possible problems

There are various other problems that can cause your plants to turn yellow. If the first three options are not the cause of your problems, check out the next options and you can probably find the solution to your problem. Yellow leaves (or any other problem) are fairly common among beginning and advanced growers.

Light Burn

Light burn is developed when your grow lights are placed too close to the plant. You can see that the leaves that are closest to the light are turning yellow. Also, it is not easy to pull out the old leaves even when the leaf is completely dead. It usually takes about 6 weeks to develop light burn for a plant. This is because the plant doesn’t produce enough leaves anymore to replace the old ones.

Even if the temperature is right in your grow room, it can happen that your lights are too close to the plant. This will cause your leaves to turn yellow. Therefore, the solution is very simple; place your lights higher above your plants. Increasing the distance will cause the plants to grow more steadily and doesn’t require the plant to work too hard anymore. When in doubt, check out the recommendations of the light manufacturer!

Please notice that some plants are more sensitive than others. It is common that plants react differently to the same height of your grow light. Pay attention to every plant and make sure that you keep optimizing the light distance.

Temperature Problems (Heat Stress / Cold Shock)

Temperature problems can be caused by lights that are too close to your plants as well. Although, it can also happen when your grown room doesn’t have the optimal temperature. Your leaves will start to turn yellow on the outside at first or they start to curl up/down. Make sure that there is good air circulation in your grow room and that you hand test the temperature of the lights.

You can hand test by placing your hand at the top of your plant underneath the light. If your hand starts to feel getting burned after 30 seconds, your light is too close. Placing your containers off the floor is also a good idea if you think the floor will get cold in the night.

Although very rare, too cold environments make your plant look pale and causes your plant to die. Especially, when you place your plant outside make sure doesn’t have to survive in temperatures close to freezing.

Not enough light

When the shell of your seedlings first crack, the plant is pale and white/yellow. Only when your plant gets enough light the leaves will turn green. You can detect this problem quickly by checking if your seedling is tall with small leaves. Your leaves will stay yellow and pale if there is not enough light. The solution is simple: add more light! Make sure you get a grow light. We wrote a complete guide to pick the best grow light for your growing.

Bugs or Pests

Getting rid of bugs or pests is very hard. The best thing you can do is prevent them getting into your grow room. You can do this by not visiting other grower’s gardens and only adopting clones if you 100% trust them. Also, try to prevent going directly to your garden from the outside. At last, if your plants are getting fresh air from outside, protect the vent with a screen that keeps bugs out.

Bugs or pests are easily spotted on your plants. You will notice that your leaves turn yellow and get spotted. These spots are probably the bugs that feast on your plant. Please act quickly after you detected these kinds of leaves or it will damage your complete harvest.

Bud Rot

It can happen that your leaves turned yellow overnight. When this happens, inspect your plants closely! Your leaves will be yellow on select parts of the biggest bud and they will fall right of your plant. You will see white, gray or brown mold growing on the inside of the cola.

Bud rot can have multiple causes. Some of them are; humidity above 60%, low temperatures, lack of air circulation, bushy plants and outdoors in rainy/humid weather. If you fix these problems, you can prevent bud rot from happening.

Sometimes yellow leaves are normal!

Keep in mind that yellow leaves are normal from time to time. It can happen that your first leaves turn yellow and die because your plant is growing. These first leaves will not get enough light anymore and they will die. Also, when it is harvest time your plant will have yellow leaves. This is very common and nothing to worry about. Also, from time to time you will have a mutation in your plant where some leaves will be completely yellow. This is no problem and your leaves can still be perfectly healthy unless there are one or two yellow leaves.

Hopefully this article helped you in getting your plant healthy again. What is a problem that you have encountered in the past that made your plant look unhealthy? How did you solve it? I would love to hear some experiences of you in the comments below!