Grow Light for Brussels Sprouts Seedlings: Height plus Hours
A grow light for Brussels sprouts seedlings turns a weak start into a sturdy transplant. University of Minnesota Extension advises bright grow lights as soon as seedlings emerge. Hang the lights close, run them 12 to 16 hours a day plus give the plants a dark period each night.
The short answer
Turn on bright grow lights as soon as Brussels sprouts seedlings emerge. University of Minnesota Extension advises lights no more than 4 inches above the seedlings, with 2 inches ideal. Give 12 to 16 hours of light daily on a timer, then harden plants off after about three weeks.
When should Brussels sprouts seedlings go under lights?
University of Minnesota Extension advises sowing Brussels sprouts seeds indoors in June for a fall crop. Use a sterile soilless seedling mix plus press the seeds ¼ to ½ inch deep. Do not use bottom heat, since regular summer temperatures are enough. Seeds should germinate in about two weeks.
Once the seedlings emerge, turn on bright grow lights above them. Illinois Extension notes the seed can be sown in seed flats 4 to 5 weeks before transplanting. Transplant at least 90 to 100 days before the first frost date.
How close plus how long should the light run?
University of Minnesota Extension advises lights no more than 4 inches above the tops of the seedlings, with 2 inches ideal. Lack of light is the major cause of elongated, skinny stems. Hang lights from chains so they can rise as the plants grow.
Plants need 12 to 16 hours of light daily. Do not leave the lights on all the time, since many plants need a dark period each night. A simple timer turns the lights off plus on automatically.
| Stage | Light plus care | Timing |
|---|---|---|
| Sowing | No bottom heat, ¼ to ½ inch deep | June for a fall crop |
| Emergence | Bright grow lights on | About 2 weeks after sowing |
| First true leaf | Starter solution diluted to half, weekly | Early seedling stage |
| Four or five true leaves | Reduce watering, start hardening off | About 3 weeks after emergence |
Source: University of Minnesota Extension plus Illinois Extension.
Which type of light works?
University of Minnesota Extension notes it is much better to grow seedlings under fluorescent or LED lights than to rely on natural light alone. Standard fixtures with two cool white fluorescent tubes give adequate light plus are inexpensive.
University of Maryland Extension notes window light is seldom enough for sturdy seedlings, which stretch plus lean toward the light. Cool white tubes give mostly blue light that can produce stocky vegetable transplants. T5 tubes cost more but typically allow more rapid growth.
How to: step by step
- Sow seeds ¼ to ½ inch deep in sterile soilless mix.
- Skip bottom heat plus allow about two weeks for germination.
- Switch on grow lights once seedlings emerge.
- Suspend lights 2 to 4 inches above the seedlings.
- Program a timer for 12 to 16 hours of light daily.
- Harden off at four or five true leaves, then plant 18 inches apart.
Troubleshooting
Tall, skinny stems: lack of light. Lower the lights to 2 to 4 inches above the seedlings.
Seedlings leaning toward a window: window light is too weak. Shift them under fluorescent or LED lights.
Leaves scorched after moving outside: no hardening off. Begin with a couple of hours of sun plus wind shelter, then add more over a week.
For related reading see cannabis seedling light schedule, leggy cannabis seedlings plus hardening off cannabis seedlings. Kind Seed Co also stocks cannabis seeds.
Sources
- Growing Brussels sprouts in home gardens, University of Minnesota Extension
- Brussels sprouts, Illinois Extension
- Starting seeds indoors, University of Minnesota Extension
- Grow lights for starting seeds indoors, University of Maryland Extension
FAQ
Can Brussels sprouts seedlings grow on a windowsill?
It is not ideal. University of Minnesota Extension notes windowsill seedlings tend to be too tall with thin, bent stems. University of Maryland Extension adds that window light is seldom enough, so seedlings stretch plus lean toward it. Fluorescent or LED lights placed close to the plants give much more usable light than a window.
Should grow lights run all night?
No. University of Minnesota Extension advises 12 to 16 hours of light daily plus advises against leaving lights on continuously. Many plants need some dark period each night to develop properly. A simple timer can switch the lights on plus off automatically, which also makes the schedule easy to hold steady.
Do Brussels sprouts seeds need a heat mat?
No. University of Minnesota Extension advises against bottom heat for Brussels sprouts sown in June. The seeds germinate plus the plants grow well in regular summer temperatures. Expect germination in about two weeks. Once the seedlings emerge, switch on the grow lights above them plus begin light feeding at the first true leaf.
When should seedlings be fed?
Start when the first true leaf appears. University of Minnesota Extension advises a starter solution diluted to half once a week. After two true leaves are present, feed twice a week. When the plants show four or five true leaves after about three weeks, reduce watering plus begin moving them outside.
How far apart should transplants go?
About 18 inches. University of Minnesota Extension advises digging small holes or a furrow plus setting seedlings 18 inches apart at the same depth they grew in their pots. Illinois Extension notes transplanting should happen at least 90 to 100 days before the first frost date for your area.
