Problem: A cannabis nitrogen deficiency will cause the older, lower leaves on your plant to turn yellow, wilt away and eventually die. The plant typically appears pale or lime-colored.
The yellow leaves of a nitrogen deficiency may show signs of brown, and they will usually become soft and sort of “fold” in, before possibly turning crispy but ultimately falling off on their own.
If the yellowing leaves are at the top of your plant or the yellow leaves are mostly new growth, then you probably don’t have a nitrogen deficiency. Nitrogen deficiencies usually affect the oldest, lowest leaves first, or the entire plant becomes light-colored.
Nitrogen is a mobile nutrient, which means it can move throughout the plant as needed. Cannabis needs nitrogen to keep leaves green and make energy from light. All new leaves get plenty of nitrogen to make them green and help with photosynthesis. The leaves that get the most light are the newest, youngest leaves, so the plant “wants” to give those leaves priority for getting light.
If new leaves aren’t getting enough nitrogen, the plant will start to “steal” nitrogen from the older, lower leaves, so that it can give it to newer leaves. This is what causes the yellowing and wilting of a nitrogen deficiency.
It’s relatively normal for your cannabis plant’s leaves to start turning yellow towards the end of your flowering cycle as the plant becomes nitrogen deficient while creating buds.
However, if your cannabis plant is losing lower leaves fast due to yellowing (if yellowing and dying leaves are “climbing” up the plant from the bottom), especially in the vegetative stage before the plant is making buds, you have a problem that you will need to fix as soon as possible.
You don’t want a nitrogen deficiency in the vegetative stage!
If you notice your lower cannabis leaves turning yellow in the vegetative stage or in the beginning part of the flowering stage, your plant may be experiencing a nitrogen deficiency which will need to be treated.
It is not good if your cannabis plant is showing signs of advanced nitrogen deficiency while still in the vegetative stage. It’s normal to lose a few yellow leaves off the bottom of your plant here and there, especially with very big plants. But if you are losing a significant amount of yellow leaves, and the yellowing seems to be moving up the plant quickly, then you have a problem.
As a grower, you’re interested in how much nitrogen to give your plants at what time. The ratio of nitrogen to other nutrients has a huge effect on growth and bud formation.
Vegetative Stage – higher levels of Nitrogen (pretty much any plant food will do)
Most complete plant foods that you get at a gardening store contain high levels of nitrogen (N).
Flowering Stage – lower levels of Nitrogen (use “Bloom” or Cactus nutrients)
It’s extra important to find a nutrient system with lower levels of nitrogen for the last part of your plant’s life. Many “Bloom” or “Flowering” style base nutrients are just the ticket.
It’s normal for plants to show signs of a nitrogen deficiency as the plant gets close to harvest. This is actually a good thing! Too much nitrogen can actually prevent proper budding and can reduce the overall taste and smell of your plant. This is why all “bloom” and flowering nutrient formulas are relatively low in nitrogen.
Don’t worry about yellow leaves close to harvest! It’s normal to see a few Nitrogen-deficient leaves in the flowering stage. Nothing to worry about unless you see the yellowing leaves start climbing up the plant.
So don’t sweat it if you see your cannabis show some signs of nitrogen deficiency late in the flowering stage! Relatively low levels of nitrogen in the late flowering stage helps promote proper cannabis bud development and will increase your yields!
Solution: You can find many pre-mixed nutrients from the store which contain nitrogen or you could use nitrate from soda or organic fertilizer which are both good sources of nitrogen. In fact, almost all plant nutrients of any kind will include nitrogen. If you haven’t been providing any nutrients to your plants, try supplementing your regular nutrients with a bit more nitrogen and see if the plant starts recovering.
If you’ve already been using nutrients, then you probably don’t have a nitrogen deficiency. If you’re seeing the signs of spreading nitrogen deficiency even a week or two giving nitrogen to your plants through nutrients, then you need to figure out what else is causing the yellowing so you can stop it.
More About Nitrogen and Your Marijuana Plants
Sometimes you can get the signs of a cannabis nitrogen deficiency if the pH at the plant root zone is too low, even if the nitrogen is there. This is because when the pH at the roots is not right, your plant roots can’t properly absorb nutrients.
Nitrogen is especially important during the vegetative stage of your cannabis plants. As your plants start flowering, they will need lower amounts of nitrogen.
Nitrogen is one of the 3 nutrients that is included in almost every kind of plant food.
When looking at plant nutrients, you’ll almost always see 3 numbers listed, like 3-12-6 or 5-10-5. These numbers represent the percentage of Nitrogen (N), Phosphorous (P) and Potassium (K) contained in the bottle. Just about all plant life on Earth needs these 3 elements to grow.
The very first number, “3” in the case of the picture to the right, always displays the proportion of nitrogen in this nutrient bottle compared to the other 2 nutrients (Phosphorus and Potassium respectively).
Nitrogen is in all plant nutrient formulations because it’s vital to plant processes.
Note: During the last few weeks before harvest, marijuana plants start pulling all the remaining nitrogen from their leaves as part of the bud-making process. This causes yellowing leaves to start towards the bottom of the plant. This is part of the natural flowering process and you don’t need to fight it. You may notice that marijuana leaves are yellowing in almost all pictures of marijuana plants with big buds that are close to harvest. You tend to get smaller yields from nitrogen-toxic plants with dark green leaves at harvest.
Remember: It’s Normal For Marijuana Leaves To Start Turning Yellow As Harvest Time Approaches