Start at the height your light’s manufacturer recommends for leafy greens, then adjust based on how the plants look. Lights differ so much in power that there’s no single right distance.
Signs the Light Is Too Far Away
- Long, thin, pale stems
- Plants leaning toward the light
- Loose, floppy heads and slow growth
Lower the light a little at a time and watch for a few days.
Signs the Light Is Too Close
- Bleached, yellow or white patches on the top leaves
- Crispy or curled leaf edges nearest the light
- Leaves that feel warm under the light
Raise the light a little.
Keep Adjusting
As lettuce grows, the top leaves get closer to the light. Check the gap every week or so, and raise the light or lower the shelf to keep it about the same.
Seedlings vs. Mature Plants
Seedlings stretch quickly if the light is weak, so give them plenty of light from the start rather than raising the light high above them.
Related guide: growing Kratky under grow lights.
