How to Fix Boron Deficiency in Cannabis Plants
Boron is a micro nutrient, so cannabis only needs a little of it. When that little runs short, though, new growth suffers, flowers stay small and yields drop. Kind Seed Co shows how to spot boron deficiency, how to fix it and how to keep it from coming back.
How to spot boron deficiency
Look at the new growth
One of the first signs is discolored, wilting tips on new growth. The affected leaves may turn yellow or brown and curl downward.
Stems and leaf veins can also turn brittle and snap easily. Growth slows, plants can end up stunted, and fewer flowers form once the plant starts to bloom.
Test the soil
Leaf signs point you in the right direction, but a soil test confirms it. You can send a sample from the root zone to a testing service or use a home kit. Either way you get a real reading of the boron in your soil before you add anything.
Brittle new growth can also come from a calcium problem, so it helps to compare the signs with our guide on how to fix calcium deficiency in cannabis plants.
How to fix boron deficiency
Use a boron rich fertilizer
The simplest fix is a fertilizer that contains boron. Spread it around the base of the plant, then water well so the boron moves down to the roots. Follow the instructions on the package, because too much fertilizer can hurt your plants.
Try a foliar spray
A foliar spray or nutrient solution with boron goes straight onto the leaves. Plants absorb it through the foliage, skipping the soil and roots, so it works fast. That makes it handy when the shortage is severe.
Use sprays and solutions with a light hand. Too much boron is toxic and causes problems of its own.
How to prevent it
Time it for flowering
Cannabis needs boron most during flowering, so that is the best time to make sure your feeding plan includes it. Always measure carefully and follow the product directions.
Feed the soil
Adding organic matter helps soil hold on to nutrients. Compost and well rotted manure are good sources and add boron along the way.
Keep pH in range
Boron is easiest for plants to take up when the soil is slightly acidic to neutral, at a pH of about 6.0 to 7.0. Our guide to understanding pH and how it affects cannabis plants shows how to test and adjust it.
Small nutrient, big difference
Boron shortages are not the most common problem, but they hit new growth and flowers hard. Watch the tips of new leaves, test before you feed and keep pH steady. If several micro nutrients seem low at once, read our guides on zinc deficiency and nutrient lockout too.
FAQ
What are the first signs of boron deficiency in cannabis?
New growth tips turn discolored and wilt, and leaves may yellow, brown and curl down. Stems and veins can also turn brittle.
When does cannabis need the most boron?
Cannabis needs boron most during flowering, so that is when to make sure your feed includes it.
Can you give cannabis too much boron?
Yes. Too much boron is toxic, so follow product directions closely, especially with foliar sprays.
What soil pH helps boron uptake?
Boron is easiest for cannabis to absorb in slightly acidic to neutral soil, at a pH of about 6.0 to 7.0.
