What is Nitrogen Toxicity and How To Resolve It?

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What is Nitrogen Toxicity and How To Resolve It?

mild nitrogen toxicity

The above leaf shows early stage nitrogen toxicity. Excessive N has caused the leaf to turn extremely dark green, along with dark purple petiole visible.

Nitrogen toxicity is one of, if not the most common toxicity to experience in your plant. It is caused by too much vegetative fertilizer and can is easy to identify once its starts. Unfortunately, affected leaves do not resolve and only new growth will show that you’ve managed to equal out the soil. Nitrogen Toxicity is most common identified by the dark green shade of the leaves, this tends to be the first stage. As the toxicity continues, the leaves will begin to get a shiny glaze to them that makes them almost reflective. Stems can also turn dark shades of purple, though this isn’t always a sign of nitrogen toxicity and can also be part of the plants natural genetics.

Because autoflowers tend to require less nutrients than photoperiod plants, you may find that Nitrogen toxicity is a bit more common to experience than your photoperiod grows. Fortunately, it is quite easy to identify Nitrogen toxicity in early stages and to make the required changes to your feeding schedules.

Identifying Nitrogen Toxicity

  1. Look for leaves turning dark green. Nitrogen (N) is directly linked to chlorophyll levels and an increase in nitrogen results in darker leaves, while an N deficiency will result in leaves losing their green colouration. In the early stages of an N toxicity issue, you’ll first start to see leaves turning dark green, followed by an almost blue colouration if left untreated. Be sure to check your leaves in natural light (especially when running blurple LEDs), as it is easy to miss these initial signs when your plants all just look pink and purple.
  2. Look for darkening petiole. You can also monitor the petiole (stem leading up to the leaf) for colouration changes, though this method is a bit less reliable as some genetics cause the same purple colouration of the petiole.
  3. Look for clawing. One of the later stages of nitrogen toxicity results in clawing of the fan leaves. There are numerous conditions which can cause the leaves to claw, but nitrogen toxicity is one of the most common.
nitrogen toxicity
Later stage nitrogen toxicity showing reflective dark green leaf along with clawing.

How To Treat Nitrogen Toxicity

So you’ve found that your plant is getting too much nitrogen and you’re looking to fix the problem. Unfortunately, as touched on, leaves that have suffered from the effects of nitrogen toxicity don’t usually recover, however it is important to resolve the problem for any new growth on the plant.

If you’ve caught your nitrogen toxicity early on, when leaves are just showing exaggerated dark greens, you can simply adjust your feeding mix to offer less nitrogen based fertilizers. Though if your plants are showing severe issues you may wish to do a flush of your soil to ensure that you remove any possible build up of nitrogen in the medium. After flushing, resume feeding but with lower N.

It is vital that you check up on your plants for N toxicity regularly, for new growers they may think that the darker green leaves are something to celebrate, and the early signs of this problem may go unnoticed.

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