Cannabis nitrogen deficiency (and toxicity): Guide to spotting, fixing, and preventing problems

Nitrogen deficiency in cannabis is one of the most common problems when growing, especially for beginners. This is because nitrogen is one of the main essential elements plants need. 

This growing guide focuses on nitrogen for cannabis plants, nitrogen deficiency and toxicity, their causes, and how to fix them.

This guide is part of a series designed to break down cannabis fertilization into reliable and actionable knowledge.

watering cannabis plants veg stage - safe nitrogen levels, no nitrogen deficiency. . ph: Alicia Muzio (Grow with Jane)
Cannabis plant growing with healthy leaves. ph: Alicia Muzio (author)

Macronutrients are the main nutrients plants need to grow strong, and you can see them labeled as NPK on fertilizer packages, short for nitrogen (N), phosphorus (P), and Potassium (K).

Bottles of fertilizer with NPK 3:1:2 and CalMag labels, showing key nutrients for cannabis growth*

Here’s a guide with a summary of macronutrients (NPK), secondary nutrients, and micronutrients.

Each of these essential elements plays a vital role in the plant’s development and overall health. It’s key to understand how they work, how they interact with each other, how to recognize nutrient imbalances and their causes, and how to fix them.

Mobile vs Immobile nutrients 

In cannabis growing, knowing about nutrient mobility helps spot deficiencies early.

Nutrients are either mobile or immobile based on whether they can move within the plant. 

Mobile nutrients like nitrogen, phosphorus, and potassium can move from the older leaves to the new growth (leaves, stems, seeds and flowers).

So nitrogen deficiency shows first on the older, lower leaves. This is extremely important.

Cannabis in vegetative stage - week 5 - mild nitrogen deficiency. ph: Alicia Muzio (Grow with Jane)
Mild nitrogen deficiency in weed plant – ph: Alicia Muzio (author)

Immobile nutrients, such as calcium, iron, and all the micronutrients, can’t relocate or move inside the plant once absorbed, so deficiencies appear in new growth and top leaves.

By recognizing where in the plant issues like yellow leaves, curled tips or brown spots show up, growers can make quick adjustments to keep plants healthy and thriving.

Role of nitrogen in plant growth and development

Nitrogen is one of the most important nutrients for cannabis plants, especially during the vegetative stage. 

Nitrogen is key for making chlorophyll, the pigment used for photosynthesis. Photosynthesis is the process by which plants convert light into energy. Nitrogen is also a building block for amino acids, proteins, and enzymes, all of which are crucial for cell growth.

Light green leaves in cannabis can indicate low nitrogen. Ph: Eir Health – Unsplash

Nitrogen is needed throughout the whole cannabis plant cycle.

During the vegetative phase, cannabis plants need higher nitrogen levels to produce green leaves and strong stem growth.

As plants transition to the flowering stage, nitrogen requirements decrease slightly as the plant shifts its focus from vegetative growth to the reproductive phase with flower production.

Nitrogen concentration 160 mg/L (sufficient N). (Bernstein, 2020). no nitrogen deficiency
Nitrogen concentration 160 mg/L (sufficient N). (Bernstein, 2020)

Notice that this plant doesn’t have a nutrient deficiency, all the nutrients are provided. By the end of the flowering stage, there is a normal process called “senescence”, the leaves show chlorosis (yellowing), even if nitrogen and other nutrient levels levels are sufficient.

Figure 1. Control plant during (a) week five when no foliar deficiency symptoms were visible and (b) week six, (c) week seven, and (d) week eight, as fan leaves developed increasing levels of foliar chlorosis. (Llewellyn, D. 2023). no nitrogen deficiency.
Figure 1. Control plant during (a) week five when no foliar deficiency symptoms were visible and (b) week six, (c) week seven, and (d) week eight, as fan leaves developed increasing levels of foliar chlorosis. (Llewellyn, D. 2023)

In a recent study (Bernstein, 2021), researchers found that nitrogen levels play a big role in the chemical profile and growth of cannabis plants, especially during flowering. They tested fertilizers with different nitrogen amounts, from low to high. Researchers discovered that while higher nitrogen levels promote plant growth, they reduce the concentration of cannabinoids and terpenoids—the compounds responsible for cannabis’s effects and aroma.

Nitrogen concentration 240 - 320 mg/L  (high N). (Bernstein, 2021)
Nitrogen concentration 240 – 320 mg/L (high N). (Bernstein, 2021)

When nitrogen levels drop, cannabis plants struggle to grow. This happens because their ability to photosynthesize slows down, water management becomes less efficient, and they can’t produce enough chlorophyll—the pigment that helps them capture energy from light. But they’ve also found that low nitrogen levels can also cause stress and induce higher concentrations of cannabinoids and terpenes, so it’s still a subject that needs further studies.

Nitrogen concentration 30-80 mg/L  (low N) - Plants show signs of N deficiency. (Bernstein, 2021)
Nitrogen concentration 30-80 mg/L (low N) – Plants show signs of N deficiency. (Bernstein, 2021)

In future guides, I’ll dive deeper into the types of nitrogen available in fertilizers (nitrate (NO₃⁻), ammonium (NH₄⁺), water-insoluble nitrogen and urea, the right balance between ammonium and nitrate, and the different nitrogen sources available to help you make the best choice for your plants.

Let me know in the comments if you are interested in this topic!

Nitrogen Deficiency in Cannabis

Nitrogen deficiency in cannabis is the most common deficiency during the vegetative stage. Some common symptoms are:

Signs of nitrogen deficiency:

  • Pale green or yellowing leaves, particularly older leaves at the bottom of the plant
  • Yellowing starts from the tip of the leaf inwards the center of the leaf
  • After yellowing, the leaf becomes brown necrotic (brown) and dies.
  • Overall stunted growth
  • Weak stems 
  • Early leaf drop
  • Early or premature flowering, which can lead to lower yields
Yellowing (chlorosis) starts at the leaf tip, spreads toward the center, and progresses to brown necrosis before the leaf dies. Grow with Jane
Yellowing (chlorosis) starts at the leaf tip, spreads toward the center, and progresses to brown necrosis before the leaf dies.

Plants with nitrogen deficiency initially show mild stunting and light yellowing or paling of the lower leaves first. The yellowing of each leaf begins at the tips of the leaf and progresses toward the center.

cannabis plant nitrogen deficiency - grow with jane
The yellowing pattern starts from the tip of the leaf inwards the center of the leaf.

As the deficiency worsens, yellowing intensifies, spreading from the bottom leaves up to the middle foliage as the plant moves nitrogen from the lower leaves to the new growth.

If the yellowing starts climbing up the plant, then you must take action and find out what’s causing the block or deficiency and correct it.

In advanced deficiency stages, the affected leaves turn completely yellow, eventually becoming necrotic, brown, and dropping off.

These pictures show how nitrogen deficiency progresses over time during the vegetative stage, from early signs to more advanced stages. (Cockson et al. 2019)

If nitrogen levels are too low, cannabis plants won’t produce enough chlorophyll, leading to slow growth and weak, underdeveloped plants. This is especially critical in the vegetative stage, where a lack of nitrogen can severely stunt the plant’s growth.

Nitrogen deficiency causes

Nitrogen deficiency symptoms may appear in cannabis plants even when nitrogen is present in the growing medium. Here are some reasons why nitrogen deficiency may show up:

Small pot

Nitrogen deficiency is common for plants grown in small pots or containers. As the nitrogen in the soil mix is depleted because the plant has absorbed it all, leaves start turning yellow and the plant stops growing.

Tip: This is easily fixed by transplanting to a bigger pot with fresh substrate and adding nutrients.

Cannabis plant in a small container with N deficiency. Ph: Testeur de CBD – Unsplash

Cold temperature

Another common cause of nutrient deficiencies is cold soil temperature. Cold temperatures can make it harder for plants to absorb nutrients, especially if the soil or water is below 10°C (50°F) and this is true for nitrogen as well.

Tips: To help your plants absorb nutrients effectively, ensure the environment temperature stays above 18°C (64.4°F) and below 26°C (78.8°F) to avoid cold soil.
If you’re growing in cooler conditions, consider using a heating mat or placing your plants in a warmer area to maintain optimal temperatures for nutrient uptake.
Water temperature should be around 18°C to 22°C (64.4°F to 71.6°F) for optimal oxygen and nutrient uptake but it may vary with the environmental conditions and setup.

Wrong pH

A common cause of nitrogen deficiency is improper pH levels in the root zone. Cannabis plants need the pH to be within a specific range to absorb nutrients effectively—typically between 5.5 and 6.5, in soil could be around 6 and 7. If the pH falls way outside of this range, even if nitrogen is present, the plant’s roots may be unable to take it up.

Tip: Check out the pH and EC of the inflow and runoff water if you suspect a nutrient deficiency. Calibrate your meters correctly for accurate results.

Try to keep pH around 5.5 – 6.5 in soilless media for better results. pH Crystalweed – Unsplash

Nutrient antagonism

Certain elements can interfere with nitrogen uptake in cannabis, leading to deficiency symptoms even when nitrogen is available. One of the main antagonists are potassium (K) and calcium (Ca). 

When there’s an excess of potassium or calcium in the soil or nutrient solution, it can damage the plant’s ability to absorb nitrogen properly. This can result in nitrogen deficiency, despite sufficient nitrogen levels in the soil. Balancing all essential nutrients is key to ensuring your plants can absorb each one effectively and avoid imbalances that could stunt growth.

Tip: Don’t overapply PK boosters (they contain high phosphorus and potassium) and cal mag products (contain calcium) to avoid nutrient antagonism and nitrogen deficiency/block.

Bottles of fertilizer labeled "PK Booster" and CalMag, highlighting essential plant nutrients.* grow with jane
Bottles of fertilizer labeled “PK Booster” and CalMag, highlighting essential plant nutrients.*

Form of nitrogen

Organic forms of nitrogen (labeled as slow-release fertilizers and “water insoluble nitrogen”) take longer to become available to plants because they need to be broken down by microorganisms in the soil, a process that occurs more slowly compared to synthetic fertilizers. This can also manifest as a deficiency in the short term. 

Tip: These forms of nitrogen shouldn’t be used to correct deficiencies if possible. (compost, slow-release fertilizers, and “water insoluble nitrogen”). Try instead fertilizers that contain fast acting nitrate nitrogen for a quick fix.

Urea is a widely used, affordable nitrogen fertilizer that dissolves in water and provides fast (or slow) nutrient release, depending on the formula. While urea can readily absorbed by plant roots, the excessive application of urea can lead to plant damage or “burn”. Choose products formulated for cannabis for better results.

Watering issues

Additionally, overwatering or poor drainage can lead to root problems that also limit nutrient uptake. 

Tip: Make sure that you water until 10% runoff if you are growing in peat, coco, and pre-fertilized soil mixes. Take out the runoff water after an hour so the plants don’t absorb it again.

avoid overwatering cannabis plants
Overwatering can cause nutrients to leach out of the substrate

How to fix Nitrogen deficiency

Nitrogen deficiency is one of the most common cannabis deficiencies. Ensuring the right balance of nutrients, monitoring pH, and providing proper watering practices are key to preventing nitrogen deficiency.

First, make sure you’ve read all the possible causes in the section before this and apply the fixing tips if necessary. If everything seems to be fine and the nitrogen deficiency is still there, then nitrogen levels may be too low in the soil mix.

If nitrogen levels are too low, adding water-soluble nitrogen, like nitrate, might solve the problem quickly.

Photos week by week of nitrogen deficiency:

Nitrogen deficiency week 3:

Figure 2. (a) Lower leaves starting to yellow from nitrogen deficiency in week three. (Llewellyn, D. 2023) - Grow with Jane blog
Figure 2. (a) Lower leaves starting to yellow from nitrogen deficiency in week three. (Llewellyn, D. 2023)

Nitrogen deficiency week 4:

Figure 2. (b) nitrogen deficiency progressing on fan leaves from mild (top) to severe (bottom) by week four. (Llewellyn, D. 2023) - grow with jane blog
Figure 2. (b) nitrogen deficiency progressing on fan leaves from mild (top) to severe (bottom) by week four. (Llewellyn, D. 2023)
Figure 2. (b) nitrogen deficiency progressing on fan leaves from mild (top) to severe (bottom) by week four. (Llewellyn, D. 2023) - grow with jane
Figure 2. (b) nitrogen deficiency progressing on fan leaves from mild (top) to severe (bottom) by week four. (Llewellyn, D. 2023)

Nitrogen deficiency week 5:

Figure 2. (d) Nearly all fan leaves are yellowing and browning, with stem discoloration and early yellowing of sugar leaves by week five. (Llewellyn, D. 2023). - grow with jane blog
Figure 2. (d) Nearly all fan leaves are yellowing and browning, with stem discoloration and early yellowing of sugar leaves by week five. (Llewellyn, D. 2023).

Many commercial nutrient formulas branded for cannabis growing in the vegetative stage come with an adequate ratio of N to phosphorus and potassium (e.g. NPK 3:1:2).

Bottles of Urea Nitrogen and NPK 3:1:2 fertilizer, emphasizing nitrogen for cannabis cultivation.* - grow with jane blog
Bottles of Urea Nitrogen and NPK 3:1:2 fertilizer, emphasizing nitrogen for cannabis cultivation.*

After fertilizing with nitrogen or a balanced NPK formula, plants should start recovering within a week.

Completely yellow or brown leaves won’t recover and can be cut out but pale green leaves should recover their healthy-looking green tone.

Healthy plants with green leaves – ph: Crystalweed – Unsplash

Nitrogen toxicity in cannabis

Signs of nitrogen toxicity (excess)

  • Leaves turn dark green (increase in photosynthetic pigment concentrations)
  • Leaf tips turn brown and necrotic (dead tissue)
  • Leaf tips and leaves curling down (clawed leaves)
  • Necrotic brown leaves with curly burnt tips 
  • Reduced bud size during flowering
  • Excessive leaf growth. Plants more susceptible to pests and diseases
  • Flowering may be delayed with excess nitrogen
  • Bad-flavored flowers, harsh to smoke
Dark green leaves with brown or yellow tips indicate excess nitrogen. Ph: Joe Ciciarelli – Unsplash

Causes of nitrogen toxicity

Overapplying fertilizers with nitrogen

Applying excess nitrogen can lead to nutrient lockout, where the plant struggles to absorb other essential nutrients, ultimately affecting flower production. 

High nitrogen levels can cause nutrient uptake competition, resulting in nutrient antagonism that limits the plant’s ability to absorb potassium, creating a relative potassium deficiency even when potassium levels in the soil are sufficient.

Too much nitrogen can cause toxicity, harming the plant and reducing yields. Bad taste in buds with overfertilization is also very common.

Cannabis leaf with necrotic tip due to nitrogen toxicity Ph:  Elsa Olofsson  - Unsplash
 - grow with jane blog
Cannabis leaf with necrotic tip due to nitrogen toxicity Ph:  Elsa Olofsson  – Unsplash

N toxicity in pre-fertilized growing media

Be cautious when using pre-fertilized soils, especially for young plants. Seedlings should not be grown in these types of media. While these soils may seem convenient, they can sometimes cause “nutrient burn” by providing too much fertilizer too quickly. Overwatering can release even more nitrogen, making the situation worse.

Plant with excess nitrogen showing clawed dark leaves. Ph: Crystalweed – Unsplash

Pre-fertilized substrates and slow-release fertilizers may not be the safer option for cannabis growing, as temperature also influences the release rate. Under temperatures above 21°C (69.8°F), the fertilizer releases faster than expected and can cause a nutrient burn or toxicity.

Tip: If you’re transplanting established plants into pre-fertilized soil, that’s fine, but this is best suited for plants in the vegetative stage, especially if you plan on training them for a longer period. 

For autoflowers or plants you want to harvest sooner, it’s better to avoid pre-fertilized soil with slow-release nutrients. Excess nitrogen during the flowering stage can actually reduce your yield.

transplant cannabis vegetative stage
Transplanting plants in the vegetative stage into pre-fertilized soil

How to fix Nitrogen toxicity

If you notice some form of nitrogen toxicity, you can try leaching/flushing the soil with water until there is 20 – 30% runoff. Resume feeding with a diluted nutrient solution, ensuring balanced levels of nitrogen.

Monitor runoff for proper electrical conductivity (EC) to avoid further overfeeding, and adjust your feeding schedule accordingly. Always start with lower nutrient doses and gradually increase.

Summary

Nitrogen is essential for cannabis growth, but both deficiency and toxicity can cause problems.

Low nitrogen levels lead to slower growth in cannabis plants due to reduced photosynthesis, poor water management, and limited production of pigments essential for energy capture (chlorophyll). The studies cited below found that when nitrogen levels are low, the plant experiences stress, which can trigger increased production of secondary metabolites like cannabinoids and terpenoids. However, severe nitrogen deficiency can harm overall plant health and development.

Nitrogen concentration 30-80 mg/L (low). Ph: (Bernstein, 2020)
Nitrogen concentration 30-80 mg/L (low). Ph: (Bernstein, 2020)

Conversely, too much nitrogen can harm growth, either through toxicity or by disrupting the plant’s ability to process carbon effectively. High nitrogen levels support vigorous growth and the production of primary metabolites nitrogen-rich compounds, such as chlorophyll (for green leaves), but they may reduce secondary metabolite levels (cannabinoids and terpenes). This happens because the plant prioritizes creating compounds that rely on nitrogen, rather than those like cannabinoids and terpenoids.

Nitrogen concentration 240-320 mg/L (high). (Bernstein, 2020)
Grow with jane blog
Nitrogen concentration 240-320 mg/L (high). (Bernstein, 2020)

The studies cited on this matter and most growers’ anecdotal evidence show that nitrogen levels need to be just right—adequate but not excessive—to support healthy growth and function. Striking the right balance with adequate nitrogen ensures healthy growth while maintaining optimal secondary metabolite (cannabinoids and terpenes) production, critical for cannabis quality and potency.

Sufficient Nitrogen concentration: 160 mg/L (Bernstein, 2021)

Conclusion

By choosing the right fertilizers and adjusting nutrient ratios, you can keep your plants healthy and thriving. Every plant is different, so stay attentive to their needs.

Nitrogen deficiency usually happens because of shortages or imbalances in what the plant gets—like the nutrient mix, type of soil, or added fertilizers. But even if a nutrient is supplied at the right levels, deficiencies can still appear due to other reasons like nutrient lockout in the soil, competition with other elements, uptake antagonism, or an off-balance pH in the root zone.

Measure pH with pH stripes if you don’t have a pH meter

Troubleshooting plant issues is more complex than simply matching symptoms to a nutrient deficiency chart. Successful problem-solving requires a holistic approach, taking into account the overall nutrient profile, pH stability, environment and how different elements interact with each other.

Regularly inspecting your cannabis plants under white or natural light for signs of nutrient deficiencies is a crucial habit for any grower.

Often, by the time visible symptoms like yellowing leaves, necrotic tips, or stunted growth become obvious, the plant has already been experiencing the deficiency for several weeks. This delay can significantly impact overall health and yield, making early detection critical.

Healthy cannabis plant in flowering - ph: Premium Cultivars - Unsplash
Healthy cannabis plant in flowering – ph: Premium Cultivars – Unsplash

Let me know in the comments if you have any questions or have faced nitrogen issues in your grow.

In the next guide of this series, we’ll explore the role of Phosphorus (P) in cannabis fertilization. Stay tuned and happy growing!

Sources:

Llewellyn, D., Golem, S., Jones, A. M. P., & Zheng, Y. (2023). Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants, 12(3), 422. https://doi.org/10.3390/plants12030422

https://www.mdpi.com/2223-7747/12/3/422

Cockson, P., Landis, H., Smith, T., Hicks, K., & Whipker, B. E. (2019). Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences, 9(20), 4432. https://doi.org/10.3390/app9204432

https://www.mdpi.com/2076-3417/9/20/4432

Saloner, A., & Bernstein, N. (2021). Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products, 167, 113516. https://doi.org/10.1016/j.indcrop.2021.113516

https://www.sciencedirect.com/science/article/pii/S0926669021002806

Saloner, A., & Bernstein, N. (2020). Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science, 11. https://doi.org/10.3389/fpls.2020.572293

https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.572293

Photos and images:

Alicia Muzio (Author) https://growithjane.com/author/alicia/

Stock photos from photographers: https://unsplash.com/

*AI-generated images of fertilizer bottles highlighting key fertilizer labels for reference purposes only, created with https://www.canva.com/dream-lab 

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