Definition - What does Leaves Curling mean?
Leaves curling on a cannabis plant, sometimes referred to as 'cupping' or 'canoeing' leaves, are an indication of an unhealthy plant. This may be due to a watering issue—either too much or too little. This could also be due to any number or combination of nutrient deficiencies. Improper pH could also cause curling leaves on cannabis.
It is critical to properly identify the specific issue causing the curling leaves before attempting to correct it or further damage may be done to the plant in trying to remedy the wrong issue.
MaximumYield explains Leaves Curling
Overwatering cannabis will cause the leaves to curl downwards, be ridgid and tight, and often turn yellow. Underwatering cannabis will often cause a drooping of the leaves and ultimately they will turn brown.
Curled leaves coupled with severe discoloration or speckling throughout the leaf may be a pH issue; testing the media of your cannabis plants can often help to avoid this particular issue.
If the leaves develop a brown spot towards the ends and begin to curl during the vegetative phase, this could be a phosphorous deficiency.
If the fan leaves under the buds discolor and curl during the flowering stage, this too could be a phosphorous deficiency.
If younger leaves turn yellow—veins and all—and the tips begin to curl, this could be a sulfur deficiency.