Learn | 05.20.2023

Nitrogen Toxicity In Weed: How To Fix It

Here's what to do when your plant has an excess of nitrogen.

Cannabis plants can suffer various issues, from root rot and purple leaves to unwanted pests like thrips. Some issues are more common than others.

Once your plant starts showing signs of stress, you must take action if you want a bountiful harvest. After all, keeping your cannabis plants under stress for long periods of time will result in a poor harvest, stunted growth, and low-quality buds come flowering time.

One of the most common issues that cannabis plants encounter is nitrogen toxicity. Fortunately, it’s very preventable and manageable once it kicks in. Keep reading for more information about detecting nitrogen toxicity, why it happens, and how to fix and prevent it.

What Is Nitrogen Toxicity In Cannabis Plants?

Nitrogen toxicity is when your plant has an excess of nitrogen. Like humans, animals, and other plant species, an excess of a certain element can have negative health impacts.

In terms of cannabis nitrogen toxicity, this happens when the grower is overfeeding the plant. Most plants need three essential elements to survive:

  • Nitrogen
  • Phosphorus
  • Potassium

Most plant-food products like nutrient mixes and blends will have a set of three numbers. These numbers indicate the ratio of the elements named above in their respective order.

This could look like “3-12-6” or “5-10-5.”

  • The first number indicates the nitrogen level
  • The second number indicates the phosphorus level
  • The third number indicates the potassium level

In the case of cannabis nitrogen toxicity, it’s essential to know how much nitrogen is in your plant food. That way, you can better understand if your plant is dealing with nitrogen toxicity (especially if the nitrogen levels are around 5). If the grower does not follow the directions of how much plant food to administer and how often, this could result in nitrogen toxicity.

How To Detect Nitrogen Toxicity In Cannabis Plants

Your plant starts looking sad. More specifically, it starts drooping down, yellowing, or showing signs of stress. This indicates that your plant is not growing how it should be, meaning there’s likely an excess of nitrogen.

Detecting nitrogen toxicity in cannabis plants is fairly easy once you’ve determined that other reasons, like pests or light burn, are not the cause of your stressed plant. If your plant’s environment is exactly what it needs to be for that strain to thrive, and if there aren’t any pests ruining your plant, then nitrogen toxicity is likely what’s affecting it.

The most common signs of nitrogen toxicity in cannabis plants are as follows:

  • Leaves appear darker, a dark green shade that’s usually darker than normal
  • Leaves may droop and turn down
  • Yellowing leaves near the roots (nutrient burn)
  • Leaves will look like a downturned claw
  • Clawed leaves will begin to turn yellow with time
  • Clawing will continue to worsen if the plant is constantly in heat and has other pH issues (this leads to an increase in water intake that leads to an excess of nitrogen)

How To Fix Nitrogen Toxicity In Cannabis Plants

Fixing nitrogen toxicity can be pretty straightforward. Once you’ve narrowed down that your plant is suffering from nitrogen toxicity, here are some steps to fix it.

Reduce Feeding: If you’re feeding plant food to your weed plant, reduce the amount you’re giving and how frequently. It’s essential to follow the feeding schedule on your plant food’s label to ensure you’re not giving it too much or too little. Even if you are following the schedule and your plant is still suffering, reduce feeding and cut it back by half.

Find Plant Food Suitable For Each Growth Phase: Similarly, different stages of your plant’s growth may need different formulas. Make sure you use the correct plant food for each stage, especially the flowering and budding phases. As mentioned above, there are different nitrogen-phosphorus-potassium ratios in plant food, and some are more suitable for specific growth phases.

Flush The Plant: Some plants may suffer nitrogen toxicity even when you’re not feeding them extra nitrogen. This can be due to a buildup of nitrogen in the soil. If that’s the case, give your plants pH’ed water to help balance the soil and flush the extra nitrogen. Do this by watering it excessively at once.

The general rule of thumb for flushing cannabis plants is watering them with enough water that doubles or triples the soil content. You’ll want a 2:1 or 3:1 ratio of water to soil in order to flush the plant of excess nitrogen successfully. Following this, only water the plant when the soil has dried, and refrain from feeding it plant food for 7 days.

How Does Nitrogen Toxicity Affect The Quality Of Your Plant?

As mentioned, keeping your plant under constant stress will result in a low-quality crop. You want your plant to be as healthy as possible in order to reap the best rewards possible, aka, healthy and potent buds.

Nitrogen toxicity severely hinders the photosynthesis process within the plant. Taking you back to grade school, photosynthesis is the process plants use to make their food. Similar to humans, too much of one mineral or nutrient can cause adverse effects, and the same happens when plants feed on too much of one nutrient, like nitrogen.

Cannabis plants with nitrogen toxicity have a harder time performing photosynthesis. For that reason, they’re not getting as many nutrients as they need, and they’re not growing to their full extent. That leads to stunted growth in the stems, flowers, and buds.

Buds will still grow, but their quality is decreased, and their shape will be slightly misformed and different than what it should be. Nitrogen toxicity can also severely reduce the quantity of buds, meaning your harvest won’t be as plentiful as you’d hope. Lastly, these sad, misshapen, and low-quality buds will also lack potency.

How Long Does It Take for A Plant To Recover From Nitrogen Toxicity?

Luckily, nitrogen toxicity is easy to spot, fix, and remove altogether. After following the steps above and reducing feeding, finding a plant food suitable for different growth phases, and flushing the plant, it should take about a week for your plant to recover from nitrogen toxicity.

Sometimes, it even takes 5 days for the plant to turn back to normal. In order to speed up the recovery time, remove old, decayed, yellowed, and burnt leaves from the plant. This helps it focus on producing more growth rather than fixing the old and ruined leaves.

How To Prevent Nitrogen Toxicity

In terms of prevention, there are a few things you can do beforehand to ensure your plant is getting the proper dose of nutrients it needs to thrive. See the tips below.

Follow The Feeding Schedule: The main thing growers can do to prevent nitrogen toxicity in cannabis plants is to follow the exact directions on your plant food packaging. If it says to mix the food with water at precise measurements and times, follow those steps exactly.

Consider Organic Fertilizers: Some fertilizers and soil mixes contain the nutrients your plant needs but in excess. Your plant ends up absorbing these nutrients right off the bat, which can shock them. On the other hand, organic fertilizers labeled “slow release” slowly release these nutrients over time to ensure your plant isn’t in shock.

Find Plant Food Suitable For Each Growth Phase: We noted this tip above, but it’s also a great preventative measure. Different stages of your plant’s growth may need different formulas. For example, when the plants begin flowering, they don’t need as much nitrogen. Make sure you use the correct plant food for each stage, especially the flowering and budding phases.

Flush Plants When Switching Plant Food: If you decide to switch up your plant’s food depending on its growth phase, consider flushing the plants to ensure there aren’t any leftover nutrients (like nitrogen) that your plant will absorb. Use our step-by-step flushing tips above to do this properly.

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