Leggy seedlings: is it the light?
Utah State Extension says poor light is the most common cause of tall, thin seedlings.
What to do, according to Utah State
- Add supplemental light and put it close to the seedlings. For leggy seedlings the page says to keep lights within several inches, up to 6 to 12 inches.
- Space plants so leaves do not overlap and shade each other.
- Reduce fertilizer and lower the temperature.
- If seedlings lean or bend toward the light, it is usually because the light is weak or comes from one direction. Add lights and rotate the plants 180 degrees regularly.
A quick check
- Distance. Is the light within the range for your fixture type? See hanging height.
- Hours. Is the timer set to 12 to 16 hours, depending on your source and fixture? See hours per day.
- Coverage. Are the trays under the middle of the light, not at the ends? Oklahoma State says tube ends lose about 3 inches of intensity.
- Warmth. Utah State lists lower temperature as part of the fix, so check that the shelf is not very warm, for instance from a heat mat left on after germination.
Can you save them?
The sources describe preventing leggy growth more than reversing it. Once the light is fixed, new growth should be sturdier. Extension pages do not promise that stretched stems will shorten.
Sources
- Utah State University Extension: Starting vegetable seeds indoors, seeding culture and transplanting (2025)
- Oklahoma State University Extension: Lighting can be tricky when starting seeds indoors (January 2024)
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