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Growing pot plants is a whole lot of fun, plus when all is done, you end up with a pile of bud to smoke, extract THC from, and use in other ways too. However, there is nothing worse than growing your own pot and then having problems with the plants, problems which look bad and indeed can be extremely problematic. One of the issues you might encounter is that your weed plant’s leaves are turning yellow.
So, why are the leaves on my pot plant turning yellow? This is a bit of a difficult question to answer because your cannabis plant leaves could be turning yellow due to a number of reasons, 11 of which come to mind right away. Yellowing pot leaves could be due to nutrient deficiencies or nutrient burns, over heating or being too cool, an improper pH level, under watering, pests, and many other things too.
Let’s take a look at the 11 big causes of cannabis leaves turning yellow and what the solution to each issue is.
11 Reasons For Weed Plant Leaves Turning Yellow
There are actually a plethora of reasons as to why the leaves on your weed plant could be turning yellow.
Let’s take a quick look at 11 reasons why your pot plant leaves are yellowing, and the solution to each problem too.
1. Bad Watering Habits
The first reason why your weed plant leaves could be turning yellow is due to bad or improper watering. It is in fact more common to over water cannabis plants than to underwater them, and on a side note, watering at the wrong times can cause issues too.
However, it is the under watering of your weed plants that can cause the leaves to turn yellow. Simply put, if you do not provide your cannabis plants with enough water, they will dry up and turn yellow due to not having enough moisture in their system.
As we mentioned above, yes, it is more common to over water than under water cannabis plants, but it does still happen. Now, under watering is not always the cause of yellow leaves, and due to the many other causes of yellow cannabis leaves, it can be hard to identify.
However, if your weed plants perk up immediately after watering, you can be pretty sure that a lack of watering is the problem. This can be a bit of a trial and error process, but the simple solution here is to just provide your weed plants with more water.
2. Improper pH Level
One of the main and most common reasons as to why your pot plant leaves are yellowing is due to the soil having an improper pH level. This is very important, because an improper pH level, which can be either too high or too low, will cause the roots to operate well below their normal efficiency.
They won’t be able to suck up enough moisture, and even if there are lots of nutrients in the soil, pH issues will cause the roots to be unable to absorb enough nutrients, thus leading to nutrient deficiencies.
When it comes to soil, the ideal pH level for weed plants is between 6 and 7, and for hydro grow ops, a pH level between 5.5 and 6.5 is required. (it’s a good idea to get yourself an accurate pH meter, we have covered some good options here).
Just by looking, it is impossible to tell if the soil of your pot plants has the right pH level. This is why you need to get a pH pen or some kind of pH testing kit.
You need to test the soil and the water you are feeding your pot plants for the proper pH level. Now that you have identified a less than ideal pH level, you can begin to use products such as pH+ or pH- in order to increase or decrease the pH level.
Keep in mind that a little of these products goes a long way, and a few too many drops of either can create big changes, so go slow.
3. A Nitrogen Deficiency
Now, a nitrogen deficiency can be result of an improper pH level or due to bad watering habits. As we noted above, both of those issues can cause the roots of the weed plant to be unable to absorb the proper amount of nutrients, and nitrogen is a very important nutrient for weed plants.
Maybe you have been using the same soil for too long and all nutrients have been sucked out of it, maybe you do not give your plants enough nutrients, or it could be due to the other issues we just mentioned.
If there are yellow leaves near the bottom of the plant which are loose and fall off, it could be a nitrogen deficiency.
One easy solution here, besides taking care of the other problems we discussed above, is to provide your pot plants with higher levels of nitrogen.
There are many nutrient mixes out there for pot plants which are specifically intended for this purpose.
If you have had your pot plant in the same soil for more than 2 months, you may want to transplant the plant into new soil that has a fresh load of nutrients ready to go.
We have covered a massive guide on what kind of soil you should be using for the best results; you can check it out by clicking here.
4. Heat Stress or Cold Shock
Yet another cause of cannabis leaves turning yellow is due to heat stress or cold shock. Now, cold shock is less common, it can occur.
If your plants are regularly in temperatures under 10 degrees Celsius or 50 degrees Fahrenheit, it can cause the leaves to turn pale and yellow, and it can eventually kill the plant.
On the other hand, if the temperature in the grow room is excessively hot, it can cause your plant to burn and dry up, thus making it turn yellow.
If you cannot hold your hands in the grow room, especially right under the lights, without feeling uncomfortable hot, well then it is probably too hot in your grow room.
Anywhere over 28 or 29 degrees Celsius has the potential to cause this problem.
The solution here is to ensure that your weed plants always have the proper temperature for sustained growth. For one, you should definitely get an accurate and high quality thermometer, just so you can actually measure the temperature.
You need to ensure that during the night, the temperature does not drop below 60 degrees Fahrenheit, and does not exceed 85 degrees Fahrenheit during the day.
If it is too cold, you can get a heater or more lights, plus more reflective materials help too, and you can turn the ventilation back a notch too. If the grow room is too hot, you can move the lights further away from the plants, get some kind of AC unit, or you can increase ventilation to let more hot air out of the grow room.
On a side note, if you have the containers on a cold floor, it will make the whole pot plant more susceptible to cold shot.
5. Light Burn
The next reason why your pot plants might be turning yellow, especially the leaves, is due to light burn. If your leaves have light burn, you will notice that the leaves closest to the lights are shriveling and turning yellow, and the yellowing leaves won’t pull off the plant easily either.
Light burn can be really bad for pot plants, especially during the flowering stage, as you will not only burn fan leaves, but flowers or buds as well.
Light burn can happen due to a number of reasons. Some plants simply cannot handle the lights being on 24/7 during the veg cycle, so you might want to decrease lighting to 18 hours per day. Weed leaves that work too hard die early, kind of like people.
Depending on the type of grow light you have, the light could just be too close and providing your plant with either way too many lumens or too much heat, and therefore, the solution to this is to move the grow lights further away from the plants, or to get slightly weaker and cooler grow lights.
HPS and LED lights are commonly known for producing light burn.
6. Not Enough Light (for seedlings)
When it comes to seedlings, which are the really small sprouts that come out of the soil before the vegetative stage begins, a cause of yellowing leaves can be that they are not getting nearly enough light.
If a seedling that has freshly cracked out of its shell is not getting enough light, the leaves actually start off as yellow, and if they continue to not get enough light, they will probably stay yellow and never really turn green.
This can be disastrous, as this early stage is very important indeed.
If your seedling is not getting enough light, chances are that it will also be really thin and stretched vertically.
The simple and quick solution here is to just provide your seedlings with more light and more light intensity.
7. Bud Rot
Bud rot is another thing which can cause leaves to turn yellow, but of course, but rot in itself can be caused by a multitude of problems.
If your pot plant is suffering from bud rot, you will notice that there are yellow leaves on the large buds, that the yellowing appears overnight, and the yellow leaves fall out, plus these leaves are usually at the base of the buds.
Bud rot can occur due to excessive humidity levels over 60%, so try and keep the humidity below 50% whenever possible. Bud rot often occurs when temperatures are too low, but also sometimes when they are too high.
Bud rot can also occur when your plant is too bushy, has too many leaves, and if you have too many growing in an inadequate space.
If you can, keep the temperature above 75 Fahrenheit during the night, provide some good air circulation, keep humidity down, and defoliate a plant that is way too bushy.
Sometimes getting rid of a few leaves can save the others.
8. Magnesium Deficiency
Just like with nitrogen, magnesium is another very important nutrient which pot plants need for growth. As you know by now, improper watering, lighting, or an improper pH level can all contribute to nutrient deficiencies.
Maybe you are just not providing your plants with enough nutrient solutions, or maybe they are growing in dirt which is old and has had the nutrients already used up.
That said, a magnesium deficiency is generally caused by an inadequate pH level.
So, the solution to a pot plant magnesium deficiency is first to ensure that you are watering your plants properly. Next, you want to ensure that the pH level of the soil and water you are giving your plants is proper.
If this still does not work, transplanting the weed plant into new and nutrient rich soil could also help. If none of this works, there are various nutrient blends that contain magnesium, as well as many pot plant magnesium supplements too.
9. Iron Deficiency
Yet another issue which can cause the leaves on your cannabis plants to turn yellow is an iron deficiency. Once again, nutrient deficiencies such as this usually always occur due to the soil not having the right pH level.
It can be caused by improper watering habits, too much light, and being in soil which is void of nutrients.
What is odd about pot plants with iron deficiencies is that the leaves do not start green and turn yellow, but in fact, they will usually already come in yellow, and then may turn green over time.
Once again, just like with the other nutrient deficiencies we looked at so far, if you measure and maintain the proper pH level, if you engage in proper watering practices, do not overheat your plant, and maybe even provide it with fresh and nutrient rich soil, you should be able to avoid or fix this problem.
If the water you are using to feed your plants does not contain enough iron, you can always use a special plant based iron supplement in order to increase iron levels for your cannabis plant.
Related: Causes & prevention for rusty spots on your leaves.
10. Bugs & Pests
Another problem which may cause the leaves of your pot plant to turn yellow is an insect infestation, or sometimes a spider mite infestation, which are actually spiders not insects.
The bottom line is that bugs and pests of all sorts, for various reasons, can cause weed plant leaves to yellow and die. In worst case scenarios, these pests may actually eat large portions of your plants, multiple inside of them, and suck them dry of moisture.
So, of course, you need to prevent pest infestations, and if they occur, you need to take care of them quick.
This is a bit of a harder problem to combat, as there are various pests which can cause issues for your cannabis plants, and each pest requires a different approach to get rid of.
Some things like poor or too much watering, a lack of cleanliness, low or high humidity levels, low or high temperatures, and lots of ways for pests to get inside can all lead to pest infestations.
Spider mites and fungus gnats are the two most common pests which cause the yellowing of leaves, so you best find out how to take care of these two critters.
- Here is a guide to identifying and getting rid of spider mites.
- 2 Reasons for white spots on leaves.
11. Nutrient Burn
Finally, the last thing which can cause your weed plant’s leaves to turn yellow is due to nutrient burn.
Yes, that is right, just like your cannabis plant can be getting too little nitrogen, iron, or magnesium, it may also be getting too much of any or all of those nutrients.
If you are sure that the pH level is fine, the temperature and humidity is fine, circulation is good, that there are no pests around, and that your plants are definitely not getting too few nutrients, your weed plants could be suffering from nutrient burn.
This is actually a pretty severe problem and sometimes there is no good solution, at least not one that will totally repair or fix your plant.
If you have been giving your plants way too many nutrients for too long, you may have caused irreparable damage.
However, what you can do is to spend a few days flushing your plants with pure water and do not give them any new nutrients.
If this causes the leaves to go back to green from their current yellow, you know that nutrient burn was the problem.
When Not To Worry About Yellow Pot Plant Leaves
Something that we need to mention here is that weed plant leaves turning yellow is not always a bad thing. Sure, it is usually not a good thing, but in a certain case, it just does not matter.
If your weed plant is almost done flowering and is more or less ready for harvest, many of the larger fan leaves will turn yellow and fall off.
This is totally normal and it is a sign that your cannabis plant is reaching the harvesting time.
We really hope that we have been able to help you here. Yes, it is definitely stressful when you see your cannabis leaves turning yellow, and yes, often it is a sign of a major issue, an issue if left untreated can have dire consequences for your plants and your final yield.
No matter what the issue is, if your leaves are turning yellow, you need to get to the root of the problem and correct it ASAP, or else chances are that your plants will totally die.