Nitrogen Toxicity in Weed Plants

Nitrogen helps cannabis grow big and leafy, but more is not always better. Too much nitrogen leads to nitrogen toxicity, which can slow your plants and shrink your harvest. Kind Seed Co explains how to spot it, what causes it and how to bring your plants back into balance.

Signs of nitrogen toxicity

Very dark green leaves

One of the earliest signs is leaves that turn an unusually dark green. Extra nitrogen packs more chlorophyll into the leaf. A healthy green means a well fed plant, but a deep, almost glossy green can mean the plant is getting too much.

The claw

Leaves may also curl downward at the tips, a look growers call the claw. The leaves get heavy and droop. Growth can stall too, which leads to smaller yields.

Test your soil and water

Along with watching the plants, test your soil and water for nitrogen from time to time. Simple test kits give a quick reading. High nitrogen in the soil or water supply puts plants at risk, and regular testing lets you change your feeding before damage shows.

What causes nitrogen toxicity

Feeding too much nitrogen

The most common cause is overusing nitrogen rich nutrients in the hope of bigger plants. Cannabis needs nitrogen, but an excess turns into a problem. If you keep adding more fertilizer to push growth, you can end up hurting the plant. Our guide to the importance of nitrogen for cannabis plants explains how much the plant really needs at each stage.

Poor drainage

Nitrogen dissolves in water, so it can build up in soil that drains badly. Over time that buildup can reach toxic levels. Good drainage is one of the simplest ways to prevent it.

How to fix and prevent it

Balance your feeding schedule

Give your plants the nitrogen they need without going over. Too much of any nutrient can harm cannabis, so follow a balanced plan such as our feeding schedule for cannabis in soil and cut back on nitrogen once flowering starts.

Cut nitrogen and flush

If your plants already show the dark leaves and claw, lower the nitrogen in your feed right away. Then flush the medium with clean water to wash out the extra nitrogen and other built up nutrients. Our guide to flushing cannabis walks through how to do it.

Watch for lockout

A heavy excess of one nutrient can stop roots from taking up others. If new problems appear after nitrogen toxicity, read our guide on preventing nutrient lockout in cannabis.

Balanced feeding grows better weed

Nitrogen toxicity is easy to cause and fairly easy to fix once you know the signs. Keep an eye on leaf color, test your soil and water, feed with a light hand and make sure your pots drain well.