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Why Do Cannabis Plant Leaves Turn Yellow


Cannabis plant leaves turn yellow sometimes, but there’s more than one reason as to why. We’re going to explain each of the most common reasons and how to remedy them. Growing cannabis is expensive, so we want to help make sure that your plants stay healthy, green and produce great flower. If you’re a new grower, this issue may come up more frequently as you’re still learning the ropes, no worries, in many cases, it’s a fixable problem.

Insect Infestations

Mites and other insects can be attracted to cannabis plants due to the ingredients in the plant food, fertilizer and/or soil. Broad/Russet mites can cause yellowing of the leaves as they start to feast on the leaves. Leaves can also become a bronze color. This issue is very hard to clear up as the leaves are likely to die rather than recover and you don’t typically see the insects either.

What you can do is treat the plant for broad/russet mites. Even when you notice that the plant appears to look good, you should still treat the plant for several weeks. They lay eggs inside the plant, and those are rather difficult to kill. Spray your plants with the treatment before you turn the lights off for the day. Neem oil is great for treating your cannabis plants for mites.

Tip: Treat your plants for 5 weeks after you notice that there are no signs of mites.

Nutrient Deficiencies

Some nutrient deficiencies, particularly a boron and copper deficiencies, can cause yellowing of the leaves on your cannabis plant. Most of the time you’ll notice yellow spotting rather than an entire yellow leaf. With a copper deficiency, the veins of the leaf or tips of the leaf are likely to turn yellow. Copper deficiencies typically show during the flowering stage of growth.  Increase your boron additive slightly and the issue should be resolved. You’ll also want to correct pH balance issues, which are also a big factor. Boron should test between 6.0 and 6.5 pH in soil tests.

Nitrogen Deficiencies

If you have leaves on the lower portions of your cannabis plant that are turning yellow, it’s likely a nitrogen deficiency. Older leaves and those closer to the bottom are more susceptible to the issue. The leaves can actually fall off of your plant altogether.

To remedy a nitrogen deficiency, make sure that newer leaves aren’t stealing nitrogen from the older leaves. Don’t panic if you notice the issue during the last few weeks of growth though, this is pretty normal. Now, if you are seeing this issue in the vegetative state (before buds start forming), you’ll need to fix it quick. Consider changing your plant food to a pre-mixed option that includes nitrogen. If this isn’t an option for you, consider an organic option.

Too Much Fertilizer

If you’re not growing organically, over-fertilizing your cannabis plant can cause the leaves to turn yellow. It is a common problem for new cannabis growers. To remedy this, you’ll want to transplant your cannabis plant into soil that has a proper ratio of fertilizer, food and soil as soon as possible. You can also consider flushing the plant by only feeding it water for a few days.

Too much Water

As with any living plant, too much water can actually smother it. The leaves can turn yellow because the roots aren’t able to breathe. So, cut back on the amount of water you’re giving your plant and all should be fine in a week or so.

Closing Thoughts

It is important to test your plant’s soil often for proper pH levels. The sooner you catch a problem the easier it will be to remedy. If you do not properly diagnose and treat the issue that makes the leaves turn yellow, you risk losing your entire cannabis plant. Speak with an experienced grower before venturing into growing cannabis for the first time; you can avoid a lot of these issues.

Need Help Growing Cannabis? Read Leafist’s related articles:

Hydroponic or Organic – Which Method of Growing Cannabis is Best?

Common Issues When Growing Marijuana

From Seed to Harvest – A Guide to Successfully Growing Marijuana

The Differences between Growing Marijuana from Seeds and Clones

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