Last Updated on October 9, 2026
How to Start Lettuce Seeds Indoors
Start lettuce seeds indoors 8 to 6 weeks before your last spring frost and plant them out 4 to 3 weeks before it. Press the seed onto the surface of moist mix and leave it uncovered or barely covered, because lettuce germinates best in light. Keep the tray under 85°F, because lettuce is one of the few seeds that fails in warm mix.
That window is the one the Plan My Garden planner uses for lettuce. To turn it into dates, look up your last frost date by zip code or enter it on my seed starting calendar.
The lettuce seed starting timeline
| Step | When | Basis |
|---|---|---|
| Sow indoors | 8 to 6 weeks before your last frost | Plan My Garden planner |
| Seedlings come up | About 4 to 2 days later as the mix warms from 59°F to 77°F | My germination chart |
| Thin to one per cell | Once the true leaves show | University of Minnesota Extension |
| Harden off | The week before you plant out | My seed starting guide |
| Plant out | 4 to 3 weeks before your last frost | Plan My Garden planner |
| Harvest | About 45 days to maturity | Plan My Garden planner |
Do the math and lettuce spends only 2 to 5 weeks indoors. Sow 8 weeks before the frost and plant out 3 weeks before, and it is 5 weeks. Sow 6 weeks before and plant out 4 weeks before, and it is 2. That short stay is normal for lettuce. University of Maryland Extension says 3 to 4 week old transplants can give earlier harvests, skip the need for thinning and make the garden more productive. My Bibb lettuce gets three weeks in its tray before it goes out.
Step by step
- Moisten the mix. Wet the seed starting mix in a bucket before you fill anything. For my Bibb lettuce I use Black Gold potting soil.
- Fill small cells. Lettuce does not need big containers. Maryland Extension’s seed starting guide recommends cells of 3 to 6 square inches for lettuce and other greens. I use an extra-deep 6-cell tray. Soil blocks work too.
- Sow on the surface. Drop the seeds on top and press them in gently. Cover them lightly or not at all. With pelleted seed I put one seed in the center of each cell and cover it lightly.
- Cover the tray. Put a clear dome or plastic wrap over it to hold moisture, and set it in a spot that stays under 85°F.
- Uncover and light up. Take the cover off as soon as the seeds sprout, which helps prevent damping off. Hang lights 2 to 4 inches above the seedlings for 12 to 16 hours a day. Minnesota Extension calls 2 inches ideal and says plants need some dark each night. My Bibb trays also do fine on a windowsill or in the small greenhouse, but if the seedlings flop and look leggy, they need more light.
- Thin to one. Once the true leaves show, snip the extras at the soil line with scissors. Minnesota Extension warns that pulling them can damage the roots of the one you keep.
- Water gently. Until the seeds sprout, Minnesota Extension suggests misting the surface with a spray bottle so you do not wash the mix out. After that, I pour water into the tray and let the cells drink it up through the holes.
Feeding is not needed in lettuce’s short stay indoors. Maryland Extension says most potting mixes hold enough fertilizer to grow a seedling for at least 6 weeks. The full method for every crop is in How to Start Seeds Indoors.
Why it matters: a 2024 research review on heat and lettuce seed germination (seed science, not garden trials) found a short heat stall is reversible, the seed sprouts quickly once it cools back down, but long exposure to high heat in wet mix can push it into a deeper dormancy it will not come out of on its own. If a warm tray has not sprouted, move it somewhere cooler right away.
Lettuce seed needs light and a cool tray
How deep to plant lettuce seeds? Don’t bury it. Press the seed onto the surface of moist mix and leave it uncovered or barely covered, since lettuce germinates best in light.
- Light: University of Maryland Extension’s guide to poor germination agrees: lettuce seed should be left uncovered, because it germinates best in light.
- A light cover if you want one: for seeds that need light, University of Minnesota Extension suggests a thin layer of fine vermiculite, which lets light through and keeps the seed moist.
- Heat: Maryland Extension says soil over 85°F is usually only a problem for spinach and lettuce seed.
How fast lettuce seeds sprout by soil temperature
Lettuce sprouts fast in cool mix and quits in hot mix. These are the days to emerge from my seed germination temperature chart, which uses J.F. Harrington’s UC Davis data.
| Soil temperature | Days for lettuce seedlings to emerge |
|---|---|
| 32°F | About 49 |
| 41°F | About 15 |
| 50°F | About 7 |
| 59°F | About 4 |
| 68°F | About 3 |
| 77°F | About 2 |
| 86°F | About 3 |
| 95°F | Little or no germination |
| 104°F | Little or no germination |
The same chart puts the lettuce optimum at 60-75°F and the maximum at 85°F. A normal room is already in that range, so a heat mat is optional for lettuce. If you share a mat with peppers or tomatoes, check the mix temperature.
How many lettuce seeds per cell
| Seed | Seeds per cell | Then |
|---|---|---|
| Pelleted seed | 1 | Nothing to thin. Pellets are easy to handle one at a time. |
| Raw seed, fresh | 2 or 3 | Snip to the strongest one once true leaves show. |
| Raw seed, older packet | 2 or more | Minnesota Extension suggests extra seeds when germination rates are lower. Snip to one. |
| Sown in a row or open flat | Thinly, in rows 1 to 2 inches apart | Separate into cells shortly after the first true leaves, before the roots tangle (Maryland Extension). |
Transplant or direct sow?
Both work. Here is how I split it.
| Start indoors when | Direct sow when |
|---|---|
| You grow head types like Bibb. I start mine in 6-cell trays. | You grow leaf lettuce. I sow it direct and cut it leaf by leaf. |
| You want the earliest harvest. Maryland Extension says transplants can give earlier harvests. | You want cut-and-come-again. Direct sowing allows tighter planting. |
| You grow crisphead. Maryland Extension calls it hard to grow because it needs a long, cool season, and suggests starting seed indoors. | You are sowing small squares every couple of weeks for a steady supply. |
The planner gives lettuce start-indoors and plant-out weeks. Lettuce made my list of 10 crops you can direct sow before your last frost, so you can also do both: transplant a few heads for an early start and sow leaf lettuce outside. Either way the trick is small, frequent sowings, a square or two every couple of weeks, so it never all bolts at once.
Hardening off and planting out
Harden lettuce off for about a week before it goes in the ground. Move the tray outside on a shady day for a couple of hours, then leave it out a little longer each day and slowly give it more sun. The steps are in How to Transplant Seedlings Into Your Garden, and a cold frame makes the job easier.
Plant out 4 to 3 weeks before your last frost. Lettuce can take that early start. My frost tolerance chart lists it as semi-hardy, taking a light freeze down to 28°F before it needs a cover, and Utah State University Extension says temperatures down to 32°F do not seriously damage young lettuce plants. Water the transplants in and mulch with leaves. Keep them moist and in about four weeks my Bibb heads are full.
Spacing is 4 lettuce plants per square foot, about 6 inches apart, and I drop to 3 per square for big Bibb heads. The details are on How Many Lettuce Plants per Square Foot? and my square foot gardening chart.
Where to get lettuce seed
Wood Prairie’s organic lettuce and salad greens include Buttercrunch, Black Seeded Simpson and Crispino, among others. Code PMG5 takes 5 percent off.
Quick questions
When should I start lettuce seeds indoors?
8 to 6 weeks before your last spring frost, then plant out 4 to 3 weeks before it. That is the Plan My Garden planner’s window, and it gives the seedlings 2 to 5 weeks indoors.
Do lettuce seeds need light to germinate?
Yes, they germinate best in light. University of Maryland Extension says to leave lettuce seed uncovered, or cover it very lightly and press it onto the mix.
How long do lettuce seeds take to germinate?
About 2 days at 77°F soil, about 3 days at 68°F, about 4 days at 59°F, about 7 days at 50°F and about 15 days at 41°F, from my seed germination temperature chart.
Why are my lettuce seeds not germinating?
Check heat and depth first. Maryland Extension says soil over 85°F is a problem for lettuce seed, and my chart shows little or no germination at 95°F. Move the tray somewhere cooler and keep the seed at the surface, not buried.
Is it better to start lettuce indoors or direct sow?
Both work. I start head lettuce like Bibb in 6-cell trays and sow leaf lettuce direct. Maryland Extension says 3 to 4 week old transplants can give earlier harvests and skip thinning.
Get your lettuce start week
The planner turns your zip code’s frost dates into lettuce start-indoors and transplant dates. Plan My Garden is free to start: enter your zip code and it finds your frost dates, draw your beds, pick lettuce and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors and transplant dates) from your frost dates.
Related: How Many Spinach Plants per Square Foot? · How Many Arugula Plants per Square Foot? · Seed Starting Step by Step · Seed Starting Calendar
