Seedlings too leggy? - Ask Extension
Hi we started our first attempt at growing our own seedlings to transplant by using hydroponic grow lights. We bought a container system that was high...
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Seedlings too leggy? #926624
Asked March 23, 2026, 9:37 PM EDT
Hi we started our first attempt at growing our own seedlings to transplant by using hydroponic grow lights. We bought a container system that was highly rated but the seedlings that have sprouted so far seem leggy to me and the light seems farther away then I think it should be. It’s not adjustable. Also the length of time maxes out at 12 hours. Are these too leggy and is 12 hours enough time? I had them set on the dimmest setting, should we increase it? The seedlings pictured are mostly broccoli, cauliflower and Brussels. With a couple onions and tomatoes. Could we also put them outside for a bit on warm sunny days? If they are too leggy, what should we do?
Prince George's County Maryland
Expert Response
Here is the UnMD article on lighting for growing plants.
Lighting for Indoor Plants | University of Maryland Extension
While not specifically for growing seedlings, it may give you a better understanding of light and plant growth.
You are correct; it looks as if the plants are not getting enough light. Here are some things you can try:
1. Put some support under the trays and keep the grow lights 1-2" above the tops of the seedlings. Be sure it's not too hot if the lamps generate heat.
2. Increase the exposure time to 14-16 hrs per day. Keep the time consistent.
3. Add airflow to strengthen stems using a small fan on low, gently blowing. Even 1–2 hours/day helps thicken stems and reduce flopping.
4. Your plants like lower temps. You can take them outside on days when the temp is above 60F but at first, keep them in the shade and not exposed to too much of a breeze. Plants need to be slowly transitioned from shade to part shade and then part sun to sun or the leaves will burn. This may take a week.
(THIS DOES NOT APPLY TO TOMATOES. THEY NEED WARMER TEMPS... 70F)
Good luck
Len
Lighting for Indoor Plants | University of Maryland Extension
While not specifically for growing seedlings, it may give you a better understanding of light and plant growth.
You are correct; it looks as if the plants are not getting enough light. Here are some things you can try:
1. Put some support under the trays and keep the grow lights 1-2" above the tops of the seedlings. Be sure it's not too hot if the lamps generate heat.
2. Increase the exposure time to 14-16 hrs per day. Keep the time consistent.
3. Add airflow to strengthen stems using a small fan on low, gently blowing. Even 1–2 hours/day helps thicken stems and reduce flopping.
4. Your plants like lower temps. You can take them outside on days when the temp is above 60F but at first, keep them in the shade and not exposed to too much of a breeze. Plants need to be slowly transitioned from shade to part shade and then part sun to sun or the leaves will burn. This may take a week.
(THIS DOES NOT APPLY TO TOMATOES. THEY NEED WARMER TEMPS... 70F)
Good luck
Len
Thank you! The system I got maxs out at 12 hours. Which I did not mention when I bought it. But I think I can just turn them on and off myself. For taking them outside, is it okay to take the whole tray even the seeds that haven't germinated yet? Also for the fan, the system is enclosed in like a dome structure. Should I remove this and get different lights so that the container is open and then put the fan on it? Or is opening the small vent holes in each container enough with the fan?
Thank you,
Leighton Green
Here is some info about the plants you intend to grow. Broccoli and plants in the same class, and onions are cool weather plants. Tomatoes are warm weather plants. Please read the Fact Sheets so you can get more info on how to grow them.
Growing Broccoli in a Home Garden | University of Maryland Extension
Growing Onions in a Home Garden | University of Maryland Extension
Growing Tomatoes in a Home Garden | University of Maryland Extension
I am not familiar with the grow-light system you have. In general, the dome covering is to keep the humidity raised, temperature stable and promote germination. You have to make a decision about the best way to use what you have or try a different system. You can certainly keep the lights/off on manually. If you take the dome off, I assume the lights will still be available to use. Just move the trays closer to them, use a gentle external fan and monitor the need to water the seedlings. Also, read the directions on the seed packs.
Yes, you can take the trays outside but need to keep the seeds which have not germinated moist. I have used plastic wrap draped over seeds which have not germinated.
When planting, broccoli (and plants in the same category) AND tomatoes can be planted deep; up to the first leaves. The stems will grow roots, making them more tolerant of draught.
Some things will work, and some will not. It's a learning experience.
Len
Growing Broccoli in a Home Garden | University of Maryland Extension
Growing Onions in a Home Garden | University of Maryland Extension
Growing Tomatoes in a Home Garden | University of Maryland Extension
I am not familiar with the grow-light system you have. In general, the dome covering is to keep the humidity raised, temperature stable and promote germination. You have to make a decision about the best way to use what you have or try a different system. You can certainly keep the lights/off on manually. If you take the dome off, I assume the lights will still be available to use. Just move the trays closer to them, use a gentle external fan and monitor the need to water the seedlings. Also, read the directions on the seed packs.
Yes, you can take the trays outside but need to keep the seeds which have not germinated moist. I have used plastic wrap draped over seeds which have not germinated.
When planting, broccoli (and plants in the same category) AND tomatoes can be planted deep; up to the first leaves. The stems will grow roots, making them more tolerant of draught.
Some things will work, and some will not. It's a learning experience.
Len
