Tomato indoor seedlings Leaf curling - Ask Extension
My six-week-old indoor tomato seedlings are experiencing leaf curl. They are on a grow light table with a full spectrum LED light hanging about 6 in...
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Tomato indoor seedlings Leaf curling #926142
Asked March 17, 2026, 7:53 AM EDT
My six-week-old indoor tomato seedlings are experiencing leaf curl. They are on a grow light table with a full spectrum LED light hanging about 6 in above the tops of the plants. I have up-potted them to containers 6 inches in diameter and 7 in deep in a mixture of coco coir and Ocean Forest potting soil to allow for drainage and to give the roots more room. I have an oscillating fan blowing a light Breeze on all my seedlings. Only the tomato seedlings are leaf curling. I have pepper plants, eggplant, lettuce, brassicas under the same conditions and none of them have Leaf curl. Inadequate moisture is not a problem, in fact I've been cutting back on watering and using knock out gnats (Bti) and yellow sticky traps to get rid of some fungus gnats. I put the containers up on pot feet to increase drainage.
The leaf curling starts on the lower leaves but has progressed to all of them on some of my older seedlings. After curling some of the lower branches dry up and fall off.
I have been fertilizing with a 3-1-2 fertilizer diluted to 50% the recommended concentration. A photo of that label is attached. When I up potted them I looked at the roots and they did not seem to be suffering browning or rot. Should I replant them in new dry potting media? Any recommendations would be appreciated.
Charles County Maryland
Expert Response
Here are the photos of the leaves and the fertilizer bottle
The leaf curling is unexpected since we don't see indications of a pest (mites, thrips, etc.) and presumably by now any potting mix ingredient contamination with long-residual herbicide (less likely if it's not based on compost) would have been evident long ago, but fortunately it doesn't look severe and we don't expect it to impact future growth once the plants go outside. The symptom may be caused by a combination of factors, though it's hard to determine which. Let the top of the potting mix dry before watering, and pause fertilizing the tomatoes until they are growing outside (even though the nitrogen application rate you're using is quite low). You could experiment and try potting a few plants into a different mix to eliminate that as a factor. (Any existing leaf curl will probably be permanent, but new growth emerging after the transplanting may show an improvement.)
Miri
Miri
Thanks for your quick response. Is it possible that the fan blowing on the seedlings throughout the day is drying out the leaves and causing them to curl? I wonder if I should cut back on the amount of time the fan blows (about 9 hours, on a timer, during the day)? Or should I mist the leaves with a spray bottle full of distilled water? I certainly don't want to cause mold or fungus, but the house is generally pretty dry because the heat is on in the winter. The fan is on the lowest speed. What is the optimum number of hours to put the fan on seedlings to achieve air flow and stem strengthening without causing excessive drying out?
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We don't think the fan is the issue, but it's hard to know for certain, so you could experiment and point it away for more indirect air circulation, or turn it off for now. There is no set amount of time needed for running a fan for stem-strengthening benefits or to reducing infection risk (since having the plants in the open air, as compared to under a humidity dome, generally gives them enough air movement and leaf surface drying), but two quick breezes per day (maybe five minutes? even brushing a hand over the top of the plants to jostle them should suffice).
We do not recommend misting the leaves with water: it will not appreciably raise humidity before evaporating away from the plants, and any leaf surface wetness could encourage infection if fungal or bacterial spores are present.
Miri
We do not recommend misting the leaves with water: it will not appreciably raise humidity before evaporating away from the plants, and any leaf surface wetness could encourage infection if fungal or bacterial spores are present.
Miri
