Burns on Cannabis Leaves
Burns on cannabis leaves are extremely frequent and they can have many different causes. In this article we’re going to go through some of the most common causes of burns on cannabis leaves. It’s not always due to your lights – plants can have adverse reactions to different climates, nutrients, water or dryness.
One of the most common cases of burns on leaves is due to the height of your lamps; many growers still believe that 60cm is the perfect height for a 600w bulb, and the buds end up dried up while still on the plant. The bulb height should be determined by the temperature at the tip of your plants by using a thermos-hygrometer. When your plants get burned because of the light the most affected zone is clearly the top area of the plant, which goes yellow until it completely dries up.
Another kind of burn that appears on the leaves can be due to unhealthy roots. Roots can become unhealthy for many reasons, such as extreme drought, growing in pots that are too big, watering too much or fertilizing too much. All of these things will cause your plants to start looking ugly and ending up burnt, as the roots will also end up burnt. These kinds of burns show up as small brown freckles on your plants which eventually grow and cover the entire leaf, which ends up falling off.
Many times you’ll need to spray your plants with foliar nutrients or preventive products such as pesticides and fungicides. When spraying, you need to be wary of the light as it can cause burns by magnifying droplets of water. When spraying you need to be sure that in the next couple of hours your plant won’t be receiving excessive light, regardless of whether your growing indoors or out. If you’re growing outdoors you need to spray them either early in the morning if you’re in a cold climate or just before the sun sets if you live somewhere where the temperatures don’t drop too low at night. If you’re growing indoors you’ll need to lift the lights up as much as possible until your plants dry, and if you can’t do that then you’ll need to take them out of the tent or room and spray them, placing them back in once they’ve dried. These burns show up underneath where the droplets of water were, which act like magnifying glasses and intensify the light.
One of the most least-known reasons for burns on cannabis leaves are fans. A direct breeze on your plants constantly can easily cause burns on the leaves, and sometimes it can be mind-boggling trying to figure out why they’re burnt. Even if you have a moving fan, if it’s on too strong and it shakes the plant too much the leaves will dry up faster than they hydrate, so the leaf will end up drying up and falling off. These burns tend to happen on the upper areas of plants where the fan can hit them – the plant closest to the fan is the one that will suffer the most. By lowering the speed on the fan or moving the plants further away from it you should stop the burning. This can be hard inside a small grow tent, where you should youse various fans set at the lowest temperature rather than one strong one.
These are some of the most common reasons for burns on cannabis leaves indoors, which is where it happens the most. It can also happen outdoors if the sun is too strong but it’s not very frequent.
Author: Javier Chinesta
Translation: Ciara Murphy