Nitrogen And Cannabis Plants

Nitrogen And Cannabis Plants

Luke Sholl
Luke Sholl
Last updated:

Nitrogen is one of the primary nutrients that your cannabis plants need for healthy growth. In this post, we’ll take a look at the functions of nitrogen, and let you know how you can identify and treat nitrogen deficiencies and excess.

Nitrogen is one of the three primary nutrients that plants, including cannabis, require to grow. If your cannabis plant doesn’t get enough of this important element, or excess, severe growing problems can and will occur. In this article we are taking a look at the role that nitrogen has for growing cannabis. You will also learn how you can identify, treat and prevent nitrogen deficiency or toxicity when growing weed.

What Is Nitrogen?

What Is Nitrogen?

Nitrogen, the most common chemical element in our atmosphere (also abundantly found in soil and water) is vital for all living things. For plant growth, it has a particular important role as it is needed for the production of chlorophyll, the plant pigment that is essential for photosynthesis.

Nitrogen (N) is a “primary” macronutrient for cannabis because it requires abundant amounts throughout its life, with particular high requirements in the growing stage. It shares its place as an essential plant nutrient with phosphorus (P) and potassium (K), the other two primary macronutrients. Nitrogen is also a mobile nutrient. This means your cannabis plant can draw it from older leaves to new growth if there is a scarcity. This is why a nitrogen deficiency normally first shows on older leaves at the bottom.

Good soil for cannabis will always have enough nitrogen, but it’s possible for it to be present in a form that is not immediately available to the plant. In that case, it’s essential to ensure a healthy presence of microbes in the soil that can break it down.

Nitrogen Fixation

For plants to take up nitrogen, natural nitrogen in its molecular form must first undergo a process known as nitrogen fixation. In this process, molecular nitrogen (N2) that occurs naturally is converted into a form that is available to plants.

First, nitrogen from the atmosphere is deposited into soil and water through rainfall. Microorganisms in the soil are then converting it into ammonia, nitrites and nitrates which can be used by plants. There are other ways how nitrogen can be “fixed”, for example some of it happens through lightning in the atmosphere, or it can be a man-made process used for producing nitrogen-rich fertilizer.

Tip: The availability of nitrogen is dependent on pH level of the soil or water/nutrient solution. When growing in soil, nitrogen isn’t available to plants at a pH level below 5.5pH. When growing in hydro or coco, nitrogen is available at a wide range of values from 2-7.

Why Do Cannabis Plants Need Nitrogen

Why Do Cannabis Plants Need Nitrogen

Cannabis needs nitrogen during its entire life cycle, although plants will need much more of it during vegetative growth. This is the reason why cannabis nutrients for “vegging” will usually have more nitrogen than flowering nutrients. The element is needed by plants to produce chlorophyll, proteins, amino acids and other important biological compounds. This is especially needed so your weed plant can grow its stem, leaves and branches. If nitrogen is not available in sufficient amounts, growing problems will occur, and your plants will most likely die.

Functions Of Nitrogen

We’ve mentioned most of these to an extent, but nitrogen functions boil down to these points:

  • Essential for vegetative growth, but also needed during flowering (although at lower amounts).

  • Essential for photosynthesis (chlorophyll production).

  • Increases plant resistances to diseases and pests.

  • Increases resistances to frost.

Needs During Early Stage

Cannabis doesn’t require nutrients in the first 2-3 weeks of growth. Not feeding early will promote the growth of roots and will benefit overall plant health. Start feeding when plants have reached a height of 15-20cm. Stick to low amounts (25-50% of recommended dosages) for the first feeds.

Needs During Vegetative Phase

From week 4 on, when your cannabis plants have entered the vegetative growing stage, they will require plenty of nitrogen, along with other essential cannabis nutrients. When using a cannabis nutrient for vegetative growth, go by the recommended feeding schedules and dosages. Know that nutrient requirements for cannabis can vary, for example, depending on the size of your plants, and how fast and vigorously they grow. A small autoflowering cannabis plant, for instance, will need less nitrogen than a large, vigorously growing feminized plant. You should also consider that overfeeding is easily possible!

Needs During Pre-Flowering

Pre-flowering occurs right before your cannabis goes into flower. In just 1-2 weeks, your plants will undergo vigorous vegetative growth, with some plants stretching considerably up to 2-3x times their current height. To accommodate this particular vigorous growth your cannabis will have maximum nutrient requirements, especially for nitrogen. The feeding schedules of commercial cannabis nutrients are usually taking this into account. Just make sure that you don’t prematurely switch to flowering nutrients before the vegetative growth of your cannabis comes to a total halt.

Needs During Flowering

When pre-flowering has commenced and vegetative growth has come to a halt, your cannabis has officially entered the flowering stage. From now on, your plants won’t grow much of anything “green” any more and will instead focus on developing their buds. Now they need less nitrogen but will want increased amounts of phosphorus and potassium. Again, good commercial flowering nutrients should accommodate this in their feeding schedules.

Tip: Nutrients for growing cannabis are typically available in two variants: one nutrient for vegetative growth, and another for flowering. Each will have the proper nutrient ratios for your cannabis depending on growing stages. This means they’ll be rich in nitrogen (N) for growth, and will have less nitrogen, but more phosphorus (P) and potassium (K), for flowering.

Nitrogen In Chemical Vs Organic Fertilizer

Nitrogen In Chemical Vs Organic Fertilizer

Nutrients for cannabis will either be mineral-based (chemical) or organic. Mineral nutrients (ie. most types of cannabis nutrients for growing in soil) provide nutrients directly to the plants, typically in a form that is readily available to the plants.

In contrast, when growing organically, one isn’t so much feeding the plants, but instead creating a suitable environment for beneficial microorganisms in the soil. Microorganisms feed on organic matter, like compost, and convert it into nutrients for the plants. Commercial (mineral) nutrients often contain nitrogen in the form of ammonium or nitrate, or both. However, growers have plenty of organic options.

Related article

How To Grow Organic Cannabis At Home

Good organic sources of nitrogen include:

  • Manures such as chicken manure

  • Compost and other organic matter, ie. grass clippings or alfalfa pellets

  • Coffee Grounds

  • Legume plants (beans, peas) alongside your cannabis. Legumes convert atmospheric nitrogen gas into a biologically-available form. This makes them excellent companion plants for your cannabis.

Nitrogen Deficiency

Nitrogen deficiency when growing cannabis is relatively common. The chances for a deficiency to occur are naturally higher with rapidly and vigorously growing cannabis plants. Nutrient requirements, and therefore the chances for a deficiency (or toxicity), also depend on the strain (not all of them are equally hungry).

What Causes Nitrogen Deficiency?

What Causes Nitrogen Deficiency?

There can be various reasons behind a nitrogen deficiency. Here are the most common ones when growing cannabis.

  • The pH at the root zone is too low, ie. pH <5.5 when growing in soil. A low pH causes nitrogen lockout, which means the plant can’t even access nitrogen when it’s present.

  • High levels of zinc and manganese have built up at the root zone.

  • Insufficient levels of nitrogen in soil.

  • Cold temperatures in the growing area.

  • Stagnant moisture in the growing medium (due to poor drainage).

  • Damaged or diseased roots from root rot, fungus or pests.

  • When growing hydroponically: too much light, which leads to algae production, which breaks down nitrogen in turn.

  • High levels of calcium, potassium or ammonia. This often results from too much lime in tap water, or using clay soils that are rich in chalk.

  • Plant stress from excessive temperatures or too much light.

  • Poor ventilation in the grow room.

  • Overfeeding (excess of other nutrients can “lock out” nitrogen).

Related article

Cannabis Nutrient Lockout: What It Is And How To Solve

How To Recognise Nitrogen Deficiency

Fortunately, nitrogen deficiency is relatively easy to spot. But know a deficiency seldom comes alone: Your plant may also show signs of other deficiencies. These are the most common signs of a nitrogen deficiency:

Early Stages:

  • Old lower leaves on your plant are gradually turning yellow. Discolouration starts at the leaf tips and moves inwards.
  • Slow or stunted growth.
  • Weak plants, which are particularly susceptible to disease and pests.

Later Stages:

  • Yellow leaves fall off.
  • Overall poor plant health.
  • Fewer and smaller buds with poor yields.

Tip: When only bottom fan leaves are yellowing with no other signs of problems with new growth on the top, it is very likely a nitrogen deficiency.

Know that yellow bottom leaves due to nitrogen deficiency is common, especially during flowering. But a few yellow leaves late in the flowering stage shouldn’t be too much of a concern if harvest is just one or two weeks ahead. Remember, you are not growing leaves, but cannabis buds. Nitrogen deficiency is much more a problem during growth.

How To Treat Nitrogen Deficiency

How To Treat Nitrogen Deficiency

How you treat nitrogen deficiency will depend on your growing method and your medium (soil, coco, hydro etc.) used.

  • In Soil

    When growing in soil and insufficient levels of nitrogen in your nutrients are the reason for the deficiency, increase nutrient amounts or add a nitrogen-rich fertilizer to your feeding regimen. For quick emergency response, quickly provide nitrogen to your plants via foliar feeding. But more commonly, a nitrogen deficiency is not caused by the grower, but by pH problems, such as those caused by overwatering and complications at the roots. The latter can happen when minerals have accumulated in the soil over time, throwing off the pH.

    If pH issues are the reason, adjust pH level of your feed/water to correct levels. The optimal pH for growing in soil is 6.5-7.0pH. If the soil is too acidic and causes lock-out (<5.5pH), flush it with plenty of plain water at the correct pH. After flushing with an amount of water equal 2-3x pot size, provide nutrients at recommended dosages, along with maintaining the proper pH.

  • In Hydro/Coco

    If you’re going in a hydroponic growing medium, check the EC/ppm in your tank. If it’s too low (<150ppm), amp up their nutrients to more appropriate levels. For a quick first-aid, foliar spray your cannabis with a low dosage of a nitrogen-rich nutrient. When growing in coco, check the amount of nutrients that you’ve provided with an on-site soil test. Based on what you learn from that, increase the nutrient intake of your plants to more appropriate levels.

Nitrogen Excess (Toxicity)

Nitrogen Excess (Toxicity)

Compared to other nutrient excesses, a nitrogen excess (toxicity) is relatively common when growing weed. This is because most nutrients contain nitrogen in ample amounts, as do commercial potting mixes.

Overfeeding, and therefore nitrogen toxicity, can happen if someone is growing with pre-fertilized soil. Many of these contain nutrients for 3-4 weeks, so premature feeding means plants will get too many nutrients. Especially smaller plants (autoflowers etc.) are susceptible to being overfed for this reason. Likewise, giving improper nutrients (such as fertilizers for a different growth stage) can also cause nitrogen excesses.

How To Recognise Nitrogen Toxicity

How To Recognise Nitrogen Toxicity

Nitrogen overfeeding when growing cannabis can show with the following signs:

  • Leaves turn a dark green colour.
  • Delayed flowering
  • Weak stems
  • Weak appearing foliage, leaves bend downwards
  • Plants have poor resistances to diseases and pests.
  • Final product has a grassy taste.

How To Treat Nitrogen Toxicity

Just like with a nitrogen deficiency, you treat a nitrogen toxicity depending on your marijuana growing method:

  • In Soil

    Getting rid of the accumulated nutrients in the soil will be your first course of action. Flush the plants with 3x the capacity of the pot with plain, pH water. After flushing, double-check the pH level at the root zone. Repeat the procedure, if necessary, until pH is in the optimal range. (Soil: 6.0-7.0ph). Proceed with giving nutrients at a low dosage, and gradually increase to recommended levels.

  • In Hydro & Coco

    Get rid of accumulated nutrients by flushing medium with pH water. When growing hydroponically, dilute or change water in your tank. Afterwards, provide feed at 50% the normal EC and gradually increase.

How To Prevent Nitrogen Toxicity

How To Prevent Nitrogen Toxicity

There are several things that you should have an eye on if you want to prevent a nitrogen toxicity. Namely, you should watch your nutrient levels, pH levels, your soil, and the type of cannabis you’re growing.

  • In Soil

    Feed your plants at adequate, recommended nutrient levels. When growing with pre-fertilized soils, do not feed in the first 3 weeks, and allow the plants to take up available nutrients.

    When growing autoflowers, be aware that they, due to their smaller size, require fewer nutrients than feminized plants. Feed 50% or 25% of the recommended dosage for your autos. No need to increase if plants grow healthy.

Related article

Do Autoflowers Need Nutrients?

  • In Hydro & Coco

    The growing medium isn’t a factor when growing in hydroponic or coco-based growing mediums. You’re already providing all of the nutrients, so it’s all about feeding at optimal levels. Just keep an eye on your nutrient EC/ppm and pH, ensuring they remain at the recommended levels. When in doubt about your feed, err to the lower end of what you assume is required. That way, you’ll be able to ensure overfeeding doesn’t become an issue. If you’re growing autoflowers, be sure to reduce feed to accommodate their lower nutrient requirements.

Luke Sholl
Luke Sholl
Luke Sholl has been writing about cannabis, the wellness potential of cannabinoids, and the positive influence of nature for over a decade. Working with several cannabinoid-centric publications, he publishes a variety of digital content, supported by strong technical knowledge and thorough research.