For a cannabis plant to grow to its full potential, it needs many different kinds of nutrients. In this guide, you will learn how nitrogen is used by a cannabis plant, and how to fix nitrogen deficiency and excess problems.
It is important to ensure your plant always has access to the right amount of nitrogen, for the right stage of its growth. Your plants will use more of it in the vegetative cycle than they will in the flowering phase.
If you any questions about how nitrogen is used by a cannabis plant, that aren’t covered here, feel free to ask for help in our cannabis growers forum
- What is Nitrogen
- How is Nitrogen used by Cannabis Plants
- Nitrogen Deficiency in a Cannabis Plant
- Nitrogen Toxicity or Excess in a Cannabis Plant
What is Nitrogen
Nitrogen is found in all living things. It is used to make parts of DNA and RNA and is vital to life as we know it.
A healthy cannabis plant will have around 3-4% nitrogen in its plant matter above ground. This is higher than any other element.
Nitrogen is used a lot by a cannabis plant throughout its whole life cycle, and is considered a “Macronutrient“. Your plant will always need nitrogen, and at no stage during your grow will you completely cut it from the plants diet (unless flushing before harvest).
Nitrogen in Plant Growth
Your cannabis plants will use nitrogen in many ways. It will be used to build the stems, branches, and leaves of your plants.
Your cannabis plant will stop making new leaves and branches when it heads further into the flowering stage. Instead it will use Phosphorus and Potassium to build flowers/ buds.
Nitrogen is also used in the process of making chlorophyll, without nitrogen, your plants will not be able to make the food they need, nor have the elements they need to grow. So, though nitrogen is used heavily during veg, you will still need a good amount during the flowering process too.
You will find when using bottled nutrients, there will usually be a “grow” nutrient, and a “bloom” or “flowering” nutrient. The grow nuits will be higher in nitrogen than the bloom nuits. You can tell what is in these nutrients by looking at the “NPK ratio”.
The three main ingredients you will find in plant food is, nitrogen, phosphorus, and potassium, N, P and K.
On these bottles, you will see three numbers, displayed like so:
NPK Ratio, will look something like this
3/2/1 ( May be displayed 3:2:1)
3 = Nitrogen
2 = Phosphorus
1 = Potassium
These are the three most important elements to cannabis plant growth, but they are not the only ones your plant will need.
Along with the NPK, your nutrients will have some trace elements like, calcium, sulphur, manganese mixed in them too. But the NPK ratio is used to give you a guideline of how much nitrogen, phosphorus and potassium are in your nutrient solution.
Grow foods, used for vegging plants will have a higher nitrogen content that bloom foods will, but, bloom food will still need nitrogen in them too, just not as much.
In the later stages of flowering, your plant will only need nitrogen to make chlorophyll so it can continue to make food from photosynthesis.
How is Nitrogen used by Cannabis Plants?
Nitrogen is used by a cannabis plant at varying levels throughout its life cycle. It will use it in large amounts during the vegetative stage, and as the plants head into the flowering cycle, the need for it will be reduced.
Vegetating Cannabis Plants and Nitrogen
A vegetating cannabis plant will have a high demand for nitrogen. This is because your plant is working hard to build leaves to catch light, and stems and branches to hold them leaves, and eventually, hold flowers.
Because of the higher need for nitrogen in the vegetative stage of a cannabis plants life cycle, “grow” nutrients will usually come with a higher nitrogen content that any other nutrient.
Flowering Cannabis Plant
As the plants begin to flower they will stop growing leaves and branches and move onto producing flowers. The cannabis buds are not made out of nitrogen, and too much can make your buds taste bad, and not be as dense as they should be.
As a result, “bloom” foods will often reduce the amount of nitrogen, and increase the amount of PK in their solution.
The nitrogen is still there though, as the plant still needs it to create chlorophyll, so it can photosynthesize. Some growers however will completely cut nitrogen out of their feed a couple of weeks before harvesting, but this of course can cause nitrogen deficiency.
Nitrogen Deficiency in a Cannabis Plant
Perhaps the most common deficiencies you will find in a cannabis plant is the nitrogen deficiency. It is used up so much by the plant, that the amount of nitrogen available to the plant from the medium can quickly be used up.
Nitrogen is a “mobile” nutrient. This means, if a cannabis plant needs some nitrogen in a specific part of the plant, it can be moved from one leaf to another.
Your plant will take nitrogen from the lower leaves, and move it to the top leaves
The Effects of Nitrogen Deficiency on a Cannabis Plant
A cannabis plant that is suffering from a nitrogen deficiency will start to show signs on the lower leaves of the plant first.
As nitrogen is needed for new growth, some of the new growth may also grow a little pale. The plant will take nitrogen from these lower leaves to feed the new growth. This will cause the leaves to turn yellow.
Because nitrogen is also used by the cannabis plant to make chlorophyll, with ut it, the plant will lose the green colour in its leaves.
As the plant can not make enough chlorophyll, the lush green look of the plant will begin to fade and turn yellow.
Without sufficient chlorophyll, the plant cannot photosynthesize, and eventually, will begin to wilt.
How to Spot Nitrogen Deficiency
Firstly, an overall pailing of the plant is a sign there is a problem. If the leaves at the bottom of the plant, and middle of new growth are yellowing, you probably have a nitrogen deficiency.
In extreme cases, the plant will start losing leaves, and stop growing, and if the problem isn’t sorted quickly, the plant can die.
How to Treat Nitrogen Deficiency in a Cannabis Plant
A nitrogen deficiency in a cannabis plant is most likely caused by 2 things:
Lack of nitrogen in the medium
The pH of the medium is not optimal
The first thing you should do whenever you are treating a cannabis plant deficiency is check the pH of the medium.
For soil grows, you should balance your medium to 6.5, and for hydroponics and coco, you should balance it at 5.8:
If the pH, is within range, then the problem is probably down to lack of nitrogen in the medium.
To fix a nitrogen deficiency in a cannabis plant, you need to add more nitrogen to the medium, but how to do this will differ on how you are growing your plants.
High Nitrogen Plant Foods
There are many plant foods you can use that are high in nitrogen, but you need foods that are going to be quickly available to your plants. Salt based nutrients are ready to be used by your plant straight away, whilst most organic foods will have to be broken down by the microbes in the medium before the plants can actually use it.
Salt Based Nutrients
Most indoor growers will use “salt based nutrients”. These are chemically altered nutrients that are readily available to the plant. When it comes to fixing a cannabis plant deficiency, salt based nutrients are fast acting and reliable, but not ideal for use with organic grows.
Grow nutrients, used for the vegetative stage, are always high in nitrogen, and increasing the amount you feed your plants will improve the situation.
Be light with the increase, Just a couple of points over your usual EC, or add around 10-15% of your usual dosage to the feed. Watch the plant for restoration of colour, it should start to look better within a couple of days.
Organic Sources of Nitrogen
With organic growing, a deficiency will take a little longer to fix. The nitrogen source you use, will need to be broken down by the microbes in the medium, and will take a few days before the plant cant start to use them.
Seaweed: Liquid seaweed will be the fastest acting nitrogen heavy food. You can feed it into the root zone, and if you’re in veg, you can foliar feed some to your plant. This will send nitrogen directly to where it is needed and will speed up the whole process.
By using worm castings you can offer a wide range of nutrients to your plants. Top dress, or water your plants with some worm castings mixed into the water. This will deliver a good amount of nutrients to your plant, and fix a nitrogen deficiency within a week
You must be careful when increasing the amount of nitrogen available to your plant. Too much can be detrimental to the growth, especially during the flowering period.
Nitrogen Excess in a Cannabis Plant
A cannabis plant needs a lot of nitrogen, but too much, can be harmful to the plant. If there is too much nitrogen in the buds after harvest, they will be harsh to smoke, and taste like hay, or grass.
It is always better to under feed a plant than over feed it. If you see a nitrogen excess in your cannabis plant, dont worry, it can be easily treated.
The Effects of Nitrogen Excess
Nitrogen is used by a cannabis plant to build stems, leaves and branches, and also to make the green pigment chlorophyll. If there is a lot of nitrogen, there will be a lot of chlorophyll.
This chlorophyll will stay in your buds, and be hard to break down after harvest. Your plants will also grow a lot of leaves, rather than flowers. For a better quality final product, you need to ensure that if you have a nitrogen excess in your cannabis plant, you fix it quickly.
How to Spot Nitrogen Excess
The first signs of a cannabis plant with a nitrogen toxicity will be dark leaves. The leaves will store up the nitrogen and chlorophyll, and they will become dark, and heavy.
A common sign of nitrogen deficiency is called “The Claw”. It is called the claw because the tips of your leaves will begin to curl downwards.
If your cannabis plant is in flower, and there is too much nitrogen available, the buds will not grow as dense as they should. Instead, they will be airy, lighter and fluffier. The flavour and smell of the final product will also be affected, as it will smell and taste like cut grass.
Treating Nitrogen Toxicity in a Cannabis Plant
“It is better to underfeed a cannabis plant, than over feed one!”
Flushing the medium
If there is too much nitrogen in your medium, it can force its way into the plant via osmosis and cause a toxicity. If you have excess nitrogen in your cannabis plant, the best thing you can do is flush the medium, which will lower the amount of nitrogen available to your plants.
For full hydroponics systems, you can either completely change the reservoir water, or dilute it with some fresh water. Make sure the pH is within the correct range, and monitor the plant for a couple of days for any changes.
You can use these guides to help you find out if your plants are over or under fed in hydro setups:
Flushing Soils, or Coco like Mediums
When you flush soils, or soil like mediums you will need a lot of water. The general rule of thumb is use 3 x water, as you have medium in your pots. For example:
10L pot, will need to be flushed with 30L of water
To fix an excess in a cannabis plant, flush the medium by pouring water through it, at the correct pH, but no added nutrients.
Monitor the EC or PPM of your run off, until it is in the range you need it to be in. This will differ from plant to plant, so if you need help here, then check out this guide on EC, or get help in the forum:
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