Last Updated on October 9, 2026
Seeds That Need Light to Germinate (and Seeds That Need Dark)
Lettuce, celery, dill and oregano need light to germinate, and summer savory and chervil germinate better with it. Press them onto the surface of moist mix and leave them uncovered, or give them only a dusting of fine vermiculite. Most other vegetable seeds, from tomatoes and peppers to beans, peas and the cabbage family, are marked “require darkness” in Iowa State University Extension’s germination table. Cover those to the depth on the packet, usually 1/4 to 1/2 inch.
Seeds that need light vs seeds that need dark: chart
| Need light: sow on the surface | Need dark: cover them |
|---|---|
| Lettuce | Tomato, pepper, eggplant |
| Celery (surface, or the thinnest cover) | Broccoli, cabbage, cauliflower, kale, Brussels sprouts, kohlrabi |
| Dill | Cucumber, muskmelon, watermelon, squash, pumpkin |
| Oregano | Beans, peas, sweet corn |
| Summer savory | Beets, carrots, radish |
| Chervil | Basil, parsley |
Onion sits in between. Iowa State University Extension marks it “lightly cover,” and Penn State Extension names onions and their relatives (Allium) among the seeds whose germination can be inhibited by light. Cover onion seed thinly rather than leaving it bare.
The dark column is Iowa State’s table, where every one of those crops is marked D. Iowa State’s table covers 25 vegetables and herbs, and only 2 of them, dill and lettuce, are marked as needing light. The rest of the light column comes from the extension sources in the next table. This list sticks to crops an extension service names. Seed company lists often add thyme, chamomile and lemon balm, but none of the extension sources behind this page says so, so follow the packet for those.
How to sow each light-loving seed
| Crop | How to sow | Planner timing (Plan My Garden) |
|---|---|---|
| Lettuce | Press onto the surface indoors, do not cover; University of Missouri Extension says fine seeds like lettuce should not be covered. Outdoors, University of Minnesota Extension plants it 1/4 to 1/2 inch deep. | 8 to 6 weeks before your last frost |
| Celery | Sow on the surface or under the thinnest cover; Virginia Cooperative Extension plants celery seed only 1/8 inch deep. | 10 to 8 weeks before your last frost |
| Dill | Sprinkle on the surface and press gently, do not bury; outdoors, Penn State Extension says to barely cover the seed. | Direct sown: 8 weeks before to 4 weeks after your last frost |
| Oregano | Place seed on top of the mix and press it into the surface, do not cover, per University of Illinois Extension. | 10 to 8 weeks before your last frost |
| Summer savory | Sow shallow; light helps germination, per University of Illinois Extension, which allows 4 to 6 weeks to grow transplants. | Not in the planner |
| Chervil | Cover very lightly or not at all, per University of Illinois Extension. Direct sow, since seedlings transplant poorly. | Not in the planner |
The sources do not all agree on depth. Lettuce is the clearest case: indoor seed starting guides leave it uncovered, while University of Minnesota’s direct seeding depth is 1/4 to 1/2 inch. In a tray, go with the surface. In the garden, keep it shallow and keep the bed moist.
How to sow seeds that need light
- Wet the mix first. Iowa State fills the tray to within 1 inch of the top, firms the mix, waters it and lets it drain before any seed goes in.
- Scatter and press. Set the seed on the surface and press it lightly so it touches the damp mix, the method Iowa State gives for light-requiring seed.
- Dust, do not bury, if you cover at all. University of Minnesota Extension uses a thin layer of fine vermiculite, porous enough to let light through while it keeps the surface moist. My soil blocks method covers seeds with the same fine vermiculite.
- Water from below or mist. Iowa State says watering from below keeps seeds on the surface from washing away. My step by step seed starting guide uses a gentle misting or bottom watering for the same reason.
- Cover with something clear. Uncovered seed dries out fast. A clear dome or plastic wrap holds the moisture, and University of Minnesota notes clear domes let light in. My seed starting guide takes the cover off as soon as the seeds germinate. Keep a covered tray under a grow light, not on a sunny windowsill; UNH Extension warns that direct sun on a covered tray can raise the temperature enough to kill the seeds.
- Give them light now, not later. UNH Extension hangs fluorescent lights 6 to 12 inches above light-requiring seeds for 18 hours a day.
How to sow seeds that need dark
- Cover to the packet depth. Iowa State’s guide is usually 1/4 to 1/2 inch. UNH’s rule of thumb for most seeds is a depth of about twice their diameter.
- Block the light until they sprout. University of Minnesota sets cell packs of dark-germinating seed in dark plastic bags or under several layers of newspaper until the seeds sprout. University of Wisconsin Extension suggests foil in place of clear plastic, removed as soon as any seedlings show.
- Move them into light the day they come up. The dark need is for the seed only. Penn State warns not to confuse what the seed needs with what the seedling needs: every seedling needs light.
Most of the dark list is not fussy. UNH says other plants have no specific light requirement, and Texas A&M AgriLife Extension says most seeds do not require light to germinate. In practice, covering them to the right depth is what matters.
Celery and lettuce, the two that cause trouble
Celery is slow and particular about more than light. The UC note on my seed germination temperature chart says celery needs diffuse light and a night temperature 10 to 15°F lower than the day, with 85°F days and 70°F nights as the optimum. The same chart’s emergence data shows celery taking 16 days at a 50°F soil temperature, 12 days at 59°F and 7 days at 68°F, with little or no germination when held at a constant 77°F. Cornell’s celery growing guide keeps the soil about 70 to 75°F and expects germination in 2 to 3 weeks. Utah State University Extension adds a soak: celery seed contains natural germination inhibitors, and soaking it in water changed daily helps leach them out. Spacing and the rest of the crop are on my celery per square foot page.
Lettuce is easier. My chart shows it emerging in about 2.6 days at a 68°F soil temperature and 7 days at 50°F, with little or no germination at 95°F, so light will not rescue seed that is too hot. For head lettuce I sow pelleted Bambi Bibb, one seed in the center of each cell, covered lightly. My square foot method sows 2 or 3 seeds at each point, barely covered. More on that routine is on my lettuce per square foot page.
Quick questions
What vegetable seeds need light to germinate?
Lettuce, celery and dill, plus the herb oregano. Summer savory and chervil also germinate better with light, according to University of Illinois Extension. Iowa State University Extension’s germination table marks only dill and lettuce as needing light out of the 25 vegetables and herbs it lists. Press these seeds onto the surface of moist mix and do not bury them.
Do lettuce seeds need light to germinate?
Yes. Iowa State University Extension marks lettuce as requiring light, and University of Missouri Extension says fine seeds such as lettuce should not be covered. Indoors, press the seed onto the surface. Outdoors, University of Minnesota Extension sows lettuce 1/4 to 1/2 inch deep, so keep it shallow and moist.
Do celery seeds need light to germinate?
Yes. Cornell’s celery growing guide says the seeds need light, so do not cover them deeply. Sow on the surface or under the thinnest layer of mix, keep it moist and about 70 to 75°F, and expect germination in 2 to 3 weeks.
Which seeds need darkness to germinate?
Most vegetables. Iowa State University Extension marks tomato, pepper, eggplant, broccoli, cabbage, cauliflower, kale, Brussels sprouts, kohlrabi, cucumber, melons, squash, pumpkin, beans, peas, sweet corn, beets, carrots, radish, basil and parsley as requiring darkness. Cover them to the packet depth, usually 1/4 to 1/2 inch.
Should seeds that need light go under grow lights right away?
Yes. UNH Extension hangs fluorescent lights 6 to 12 inches above light-requiring seeds for 18 hours a day. Seeds that need dark can stay covered until they sprout, then move under lights the day they come up.
Sown right, now dated right
Light sets how deep a seed goes. Your last frost sets when it goes in. Find yours with the Plan My Garden frost date lookup, or count back the weeks on my seed starting calendar. Plan My Garden is free to start: enter your zip code, draw your beds, pick lettuce, celery and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors, transplant and direct sow dates) from your frost dates.
Related: Vegetable Seed Germination Temperature Chart · How to Start Seeds Indoors · Seed Starting Calendar
