Nitrogen Deficiency in Cannabis Plants

Nitrogen deficiency is one of the most common problems home growers run into. Kind Seed Co explains what nitrogen does, how a shortage shows up, what causes it and how to get your plants back on track before it cuts into your harvest.

Nitrogen fuels leaf and stem growth, especially in the vegetative stage. For a full look at its role, read our guide to the importance of nitrogen for cannabis plants. This page sticks to spotting and fixing a shortage.

How to spot nitrogen deficiency

Lower leaves turn yellow first

The first sign is usually yellowing on the lowest leaves. It starts as a pale green that spreads from the base of the leaf toward the tips, then deepens to a clear yellow. The plant moves nitrogen out of older leaves to feed new growth, so those bottom leaves can turn brown and drop as the shortage gets worse.

Slow, stunted growth

With too little nitrogen, plants grow slowly. The main stem can look thin and weak, and new leaves come in smaller, which keeps the whole plant short.

Smaller yields

A shortage in veg means fewer bud sites form, and fewer bud sites mean a lighter harvest.

Late flower fade is different

Some yellowing near the end of flowering is normal, as the plant uses up its stored nitrogen while buds finish. Yellow lower leaves in veg or early flower are the ones to act on. If you are close to harvest, see our guide to flushing cannabis before you add more feed.

What causes it

• Worn out soil. Plants take nitrogen from the soil, and after several grows the soil can run low.
• pH out of range. If the pH of your medium is too high or too low, roots cannot take up nitrogen even when there is plenty in the soil.

How to confirm the problem

A soil test is the most reliable check. You can send a sample to a lab or use a home kit, and either one shows how much nitrogen is in your soil. A close look at the plant also helps, and it is often how you notice something is off in the first place. Check your pH at the same time so you know whether the soil is short or the roots are simply locked out.

How to fix nitrogen deficiency

Correct the pH

If pH is the cause, bring it back into range and the roots can take up nitrogen again.

Feed a nitrogen rich fertilizer

A fertilizer high in nitrogen works quickly. Follow the label closely, because too much at once can cause nutrient burn. Soil growers can follow our feeding schedule for cannabis in soil, and hydro growers can use the hydroponic cannabis feeding schedule.

Add organic sources

Compost, manure and bone meal can add nitrogen to the soil the natural way. They release it more slowly than bottled feed.

How to keep it from coming back

• Feed on a steady schedule. Regular, balanced feedings keep nitrogen available through veg.
• Build up your soil. Adding compost, planting cover crops and rotating crops all help keep soil fertile between grows.

Nitrogen is only one of the nutrients that show up in your leaves. Our guide to spotting common deficiencies by their leaves helps you rule out the others.