Nitrogen Deficiency vs. Nitrogen Toxicity in Your Weed
Nitrogen Deficiency vs. Nitrogen Toxicity in Your Weed
When it comes to a nutrient problem in your cannabis crop, you can do more harm than good if you don’t correctly identify the problem. Nitrogen is a critical component in the proper growth and function of marijuana. Understanding this macronutrient will equip you to grow high-quality cannabis while saving yourself stress if you encounter a deficiency or toxicity issue.
✅ Understanding Nitrogen’s Role in Cannabis
When I’ve gone to survey grow operations when I worked with a consultant agency, I found that the most common problem in marijuana gardens had to do with nitrogen. I can’t count the number of times that I’ve seen canopies as far as the eye can see that was a deep yellow. This nutrient is responsible for a host of functions within our beloved marijuana crop. Let’s take a look at what nitrogen is responsible for before we outline common problems.
First and foremost, nitrogen is a crucial component in the production of chlorophyll. Some of you may remember this term from biology class, so hopefully, this time you remember! Chlorophyll is the pigment that’s responsible for the plant’s green color. More importantly, it functions as a light-absorbing pigment that enables plants to photosynthesize the Sun’s rays into food.
Without this function, plants would not exist in their current form as they do today. This key adaption is what has driven plants all over the world.
Another function of nitrogen is its role in amino acids. Amino acids are the building blocks of proteins, and without these proteins, plants would not survive. Just like with our own bodies, we require proteins to function correctly, and it’s not different for plants.
All of the required nitrogen is taken up through either the root system or through foliar sprays. The form in which nitrogen is taken by the plant is either nitrate (NO3) or ammonium (NH4). These two forms are essential to remember, but even more important is to understand the dosage.
Remember, nitrogen is the main component for your plant to produce new leaves. Besides the root system, the cannabis canopy is crucial for the survival of your cannabis plant. The leaves are the engine, the light is the fuel, and the chlorophyll is combustion. Nitrogen allows for all of these critical components to happen, so it’s with the utmost importance that you take the time to understand and respect the role of nitrogen fully.
🎯 Feeding Cannabis Nitrogen
If you’ve grown weed, then you’ve seen all the cannabis nutrient products and their display of the macronutrients N-P-K. N stands for nitrogen, the other two are phosphorous and potassium, but we’ll focus on the other two in another series.
As your cannabis plant begins to grow and uptake nutrients, the available supply of nitrogen will decrease. This means that you’ll need to feed your cannabis plant nitrogen continually. Of course, the type of nitrogen you feed your plant is dependant on the method in which you’re growing.
The most straightforward method is to buy nutrients that are considered “safe.” This means that buying a bottle of plant fertilizer that consists of an N-P-K of 10-10-10 is generally a safe standard. The reason for this is because all marijuana strains have different nutrient needs, and a gentle 10-10-10 ratio is best for starting out.
Nitrogen is quickly absorbed through cannabis, and you’ll notice fairly quickly if you gave too little or too much. Let’s take a look at identifying problems related to nitrogen.
👾 Nitrogen Deficiency
Nitrogen deficiency has to be one of the most common problems that growers face. Suddenly your marijuana plant is turning yellow. You don’t understand why the lower leaves are beginning to wither and die off, but you do see it as a problem. Before you go throwing more plant nutrient, stop and identify the problem.
It’s common that growers do more harm than good when they blindly start adding things to their cannabis crop without first identifying the issue at hand.
The biggest giveaway for nitrogen deficiency is the yellowing of lower leaves. The reason this occurs is that the plant has run out of available nitrogen to uptake. This causes higher leaves that are closer to the light to steal the lower leaves’ nitrogen. If left alone, the lower leaves will eventually fall off, and the problem will continue from bottom to top until the plant cannibalizes itself in search for nitrogen.
You’ll know if your plant is recovering if the yellowing doesn’t continue and leaves begin to regain their healthy green shade. Light green is always a sign that a nitrogen deficiency is close to happening.
The worst time for a nitrogen deficiency is at the beginning of the vegetative stage, where the plant is focusing on growing foliage that will help once the flowering stage begins. Alternatively, it’s at the end of flowering that growers tend to intentionally create a nitrogen deficiency to rid the plant of chlorophyll.
Now that you’ve identified the problem, increased the dosage of plant nutrient, you should wait a few days to confirm if your plant is recovering. Remember, patience is half the battle when it comes to growing marijuana.
The Only Time You Want a Nitrogen Deficiency
There is, in fact, a time when you actually do want a nitrogen deficiency. The only time you’ll ever want this as a marijuana grower is during the end of the flowering stage. Depending on the strain, you want your cannabis leaves to turn yellow around week 8-10 of flowering.
But why? This is a situation that is very specific to growing marijuana because it all has to do with the end product. You guessed it- it has to do with the buds that we’ll eventually smoke after the drying and curing process.
Chlorophyll as we learned, is the necessary pigment in absorbing light. Near the end of the flowering process, we’re going to sadly kill our plants to harvest them. The issue with chlorophyll is that this pigment as contains a smell similar to hay or dry grass, which we taste when smoking the finished product
Lack or excess of nitrogen in your marijuana
The easiest way to get rid of this smell and taste is by flushing out as much of the chlorophyll as possible. Growers will usually start only watering their plant with small amounts of nutrient to force a nitrogen deficiency. This is extremely apparent when you look at pictures of growers harvesting their plants. What you’ll see is large buds and most of the leaves a bright yellow color.
This isn’t an essential step because you can also get rid of excessive chlorophyll during the drying process. All you’ll need to do is leave your plants in complete darkness for a few days to speed up the dissipation of chlorophyll from the leaves.
⚠️ Nitrogen Toxicity
The opposite of a nitrogen deficiency is when we see nitrogen toxicity. This is equally as common as nitrogen deficiency because new growers tend to overdose their plants with nitrogen. It’s a fact that new growers kill their cannabis plants by loving them too much.
It’s common that growers cause nitrogen toxicity by following even the recommended dose found on their nutrient product. The recommended dose offered by nutrient companies is just a general amount because some strains will need either more or less. Once again, no strain is created equal, and this means that each strain you grow will more than likely require varying dosages of nutrient.
When encountering a nitrogen toxicity issue, you’ll see a deep shade of green on the leaves of your marijuana plant. The deep shade of green can worsen and even take on a slight deep blue hue in extreme cases. This is a very noticeable symptom and is therefore easy to identify and fix before real damage occurs to your cannabis plant..
Another noticeable symptom of nitrogen toxicity is called the “claw.” The ends of the fan leaves will point down, similar to the way a bird claw looks. This symptom is also present when overwatering cannabis plants, but if you’re not overwatering, then this should lead you to believe that you’re amid a nitrogen toxicity issue.
To add to the list of symptoms is also leaf tip burn. When too much nitrogen is added, the plant tries to get rid of it through the ends of the leaves. This results in the leaf tips looking necrotic and seemingly burned.
Nitrogen: excess vs. lack
If nitrogen toxicity is allowed to continue,then the plant will cease many necessary functions to sustain vigorous growth. You should never let a toxicity issue to gain a foothold on your plants because it will result in a more extended recovery period.
It’s dangerous to suddenly stop giving nutrients when noticing a nitrogen toxicity issue because the plant is still up taking the other necessary nutrients. If you stop giving nutrients, you may find yourself in the exact opposite situation: a nitrogen deficiency!.
Small steps are vital in not creating a bigger problem. Adding or decreasing nutrients will take a few days to show results.
🔥 The Role of pH and Nitrogen Issues
As we all know, there are a host of problems that can go wrong while we’re growing our marijuana crops. A major complicating factor for nitrogen toxicity or deficiency is when it’s accompanied by pH issues.
Depending on the medium that we’re growing in, pH plays a vital role in the health of our plants. This is extremely apparent when growing in hydro or aeroponic systems. These systems don’t have the natural buffer found in soil-grown plants. Cannabis grown in soilless systems rely on their caretakers to set the pH to a correct level that allows the plants to take up plant nutrient effectively.
If you don’t set the pH to a correct level (usually 5-6pH), then you’ll compound your problems as you see deficiencies or toxicities starting to mount up. The root zone doesn’t enjoy the wrong pH and will stop taking up nitrogen, thus creating a nitrogen deficiency.
These are just a few examples of the intricacies of growing marijuana. Most aspects of the plant are interconnected, which leads to one problem affecting another portion of the plant.
For marijuana plants to develop smoothly, the pH and dosage must be continually monitored.
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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.
Example of cannabis Nitrogen deficiency – yellow bottom leaves. Almost all plant nutrients contain Nitrogen
Nitrogen-deficient plants often appear pale or lime-colored. The leaves on this marijuana plant don’t have obvious leaf symptoms like spots or markings, but they are pale all over the whole plant. Almost lime green. The light-colored leaves are a sign the plant needs more Nitrogen (and nutrients in general). On the flip side, plants that are receiving too much Nitrogen turn dark.
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 is “climbing” up the plant from the bottom), especially in the vegetative stage before 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 an advanced nitrogen deificiency 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). These nutrient system tend to work well in the vegetative stage.
Some examples of cannabis-friendly one-part Vegetative nutrient systems…
Pretty much any complete plant food
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.
Some examples of good one-part Flowering nutrient systems…
If you can’t order online and can’t find a good one-part base Bloom formula locally, you do have other choices. Though not an ideal choice, most Cactus plant foods will contain good nutrient ratios for growing cannabis during the budding stage. So in a pinch, you can use the cactus nutrients that can be found at most gardening stores.
The first cannabis plant pictured below is showing signs of nitrogen deficiency late in flowering; nitrogen deficiency in late flowering is completely normal and even desired. The last picture is an infographic about nitrogen and your marijuana plant.
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 help 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 of 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 nutrient 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. If you aren’t sure about your root pH, learn more about pH & growing cannabis plants here.
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 3 numbers on the front of plant nutrient bottles list the amount of Nitrogen, Phosphorus, and Potassium.
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 her leaves as part of the bud-making process. This causes yellowing leaves starting 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
Occassionally a nitrogen toxicity is mistake for a deficiency. Could your plant actually be nitrogen toxic? (pictured below)
This picture shows a Nitrogen Toxicity
- Bronze or brown patches
- Brown or slimy roots
- Brown or yellow leaf tips/edges
- Buds dying
- Buds look odd
- Bugs are visible
- Curling or clawing leaves
- Dark leaves
- Drooping plant
- Holes in leaves
- Mold or powder
- Pink or purple on leaves
- Red stems
- Shiny or smooth leaves
- Spots or markings
- Twisted growth
- Wilting leaves
- Yellow between leaf veins
- Yellow leaves
This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.
A nitrogen deficiency causes the lower/older leaves of a cannabis plant to start yellowing, wilting, and dropping off on their own. Learn how to fix it.