Why are the outer edges of my plant's top leaves starting to curl?

Q:

There’s a slight curling of the outer edges of the top leaves of my plant seven weeks into my indoor grow. What should I do? No burning on the tips or anywhere else.

A:

There are several possibilities regarding what could be causing your curling leaves. Curled leaves that are not accompanied by any necrosis or browning of the foliar edges may be attributable to nutrient excess, insect damage, water, other cultural issues, or even possibly the genetics of your plant.

There is no way to give you a definitive answer without having some background information, but we can cover some of the most likely possibilities.

Not enough water can cause this symptom, but if it does not correct itself after a good drink, this is not likely the issue.

Conversely, the leaves of an oversaturated plant may curl or droop, but often this is followed by a yellow and or sick appearance of the plant too. Too much water and poorly drained soil may also set the stage for root rot, which will cause the leaves and ultimately the entire plant to collapse.

If you are growing these plants in containers or planting beds and not hydroponically, make sure that the media you are growing in is well-drained and porous so that excess water can drain through. A moisture meter can help to identify how wet your media is and whether or not this may be the cause.

Too much nitrogen to the point of toxicity can cause curling leaves as well. Performing a simple soil or media analysis will help to rule this possibility out or in depending on your results.

Your plant may also just be showing signs of stress due to cultural factors. Is the curling just on one side? This could be an environmental problem due to continual and proximal exposure to a fan.

Another likely culprit that can be easily checked and remedied is if you are growing these plants in pots and if they have become root-bound. If this is the case, scuff up the roots and pull them away from the root ball before transplanting them into a larger container.

If none of these seem to be the cause of the leaf curl that you are experiencing, the symptoms may be caused by a mite infestation.

Several different species of mites, including Broad mites, Cyclamen mites, and Russet mites may be feeding on your plant leaves and leave curled leaves in their wake as a result of a substance that they inject into the foliage while feeding.

Generally, though, there will be other symptoms appearing shortly after you notice the curling such as a change of color (yellow to brown) or a speckled appearance to the leaves.

If you have ruled out all of the above, there is possibility that the particular species of plant that you are growing has the naturally tendency to have curled leaves. This is not an unknown characteristic of some strains of plants.

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Written by Chris Bond
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Chris Bond is the manager of the McKay Farm and Research Station at Unity College in Maine. His research interests are with sustainable agriculture, biological pest control as well as alternative growing methods. He is a certified permaculture designer and certified nursery technician in Ohio and a certified nursery professional in New York, where he got his start in growing.

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