When to Plant Lettuce: Sow Early, Finish Before the Heat

Sow lettuce as soon as the soil can be worked, about 2 to 4 weeks before your average last spring frost, and stop about 50 days before your normal daily temperature reaches 70°F. Sow again once late-summer heat breaks, and finish about nine weeks before your first hard freeze. In Chicago that is March 17 to April 22 in spring and August 7 to September 12 for fall; in Dallas it is February 2 to March 7 and September 29 to October 9.

Most guides stop at a count of weeks before frost. We tested those counts against NOAA 1991–2020 normals¹ for 37,563 lower-48 ZIP codes, set nine published local windows beside them, and built dates for 22 cities in spring and 18 in fall. Everything below uses air temperature as a stand-in for soil temperature, because our NOAA data has no soil readings.

Spring lettuce planting dates for 22 cities

Published counts cluster around 2 to 4 weeks before the last frost: the Old Farmer’s Almanac says to direct-seed then,² Colorado State lists lettuce among hardy crops that can go in 2 to 4 weeks ahead,¹¹ and Utah State says 2 to 3.⁶ Each window below opens on the later of two dates: four weeks before the median last frost, or the day the normal daily mean air temperature reaches 40°F, the soil floor named by Utah State,⁶ Texas A&M¹³ and Illinois Extension.⁵

It closes 50 days before the daily mean reaches 70°F. Illinois Extension says leaf lettuce reaches full size in 50 to 60 days⁴ and gives the comfort zone:

thrives when the average daily temperature is between 60 and 70°F

On the northern Plains the window runs 39 days (Fargo, April 12 to May 21). Gulf and Atlantic coast gardens start in winter: Houston from January 5 to February 24, Charleston from January 7 to March 12. Central Texas is tight, with 16 days in Austin. Portland and Seattle never reach a 70°F normal mean, so they have no heat deadline at all.

Cold: how early is too early

Across the lower 48, four weeks before the median last frost falls before the normal air mean reaches 40°F in 9.6% of ZIP codes. Colorado State lists leaf lettuce germinating from a 35°F minimum, with seedlings up in 4 to 10 days,¹¹ and Utah State says seed sown into 55–65°F soil emerges in 7 to 10 days.⁶

Frost is rarely the problem. Utah State says temperatures down to 32°F do not seriously damage young plants,⁶ and Maryland’s commercial guide says properly hardened transplants tolerate 20 to 25°F.⁹ Our frost-cover guide groups lettuce with crops that suffer in the upper 20s°F. For an indoor start, the Almanac counts 6 to 8 weeks before the last frost and sets transplants out 3 to 4 weeks before it;² our seed-starting guide compares other schedules.

Heat: the spring deadline

Warmth ends the crop. Maryland Extension says increasing day length and high summer temperatures usually cause seedstalk formation, called bolting, and a bitter flavor.³ Utah State puts the goal plainly:⁶

Lettuce tastes best when plants grow rapidly and mature before the heat of summer.

Sowing on the median last-frost date is too late for a 50-day crop in 21.7% of the ZIP codes that reach a 70°F mean, because 50 days later the mean is already above 70°F. Sowing on the last day of the Almanac’s window, two weeks before the last frost, fails in only 0.6%, and for baby greens (the Almanac gives 25 to 40 days) sowing on the last-frost date fails in 2.0%. So the common rule holds up in spring. Where a 70°F mean occurs (84.6% of ZIP codes), the median window is 33 days and 68% get 30 days or more.

How hot is too hot: nine temperature rules compared

Every source agrees lettuce is a cool-season crop, but the numbers differ. This table sets them side by side. The widest gap is the germination ceiling, anywhere from 70°F to 95°F.

The 95°F figure from Clemson is for raw seed, and Clemson says primed seed ensures optimum germination at varying temperatures.⁷ The University of California’s guidelines say germination is inhibited above 86°F.¹⁰ Maryland’s guide says seed enters dormancy above 85°F and that many vendors offer primed seed.⁹ For a home garden, the safe reading is to sow after the soil cools below about 80°F, the figure Utah State gives for reduced germination and Texas A&M for seed-stalk formation.^6,13

Fall lettuce planting dates: wait for the cool, then count back

Fall lettuce is easier to ruin by sowing too early than too late. The published counts differ: the Almanac says 6 to 8 weeks before the first fall frost,² Bonnie Plants says 4 to 8,¹⁶ Utah State says to plant 50 to 75 days before maturity and finish 1 to 2 weeks before the first fall frost,⁶ and one gardening blog says 60 days.¹⁸ Google’s AI Overview for “when to plant lettuce for fall” gave 6 to 8 weeks when we checked on October 14, 2026.

A count back from frost ignores summer. Among ZIP codes that reach a 70°F summer mean, eight weeks before the median first frost falls while the normal mean is still 70°F or higher in 67.6%, and still 75°F or higher in 9.3%. Delaware Extension explains why that matters: in southern Delaware average daily soil temperatures are typically above 80°F through the third week of August, and heat can induce thermal dormancy that prevents germination.⁸

83% of the varieties fully or partially bolted

That was a trial in which transplants went out inside Delaware’s recommended August window; the specialist concludes growers should use heat-tolerant varieties for fall.⁸ Our fall window therefore opens on the first day after the summer peak when the normal mean falls below 75°F, an air-temperature proxy for soil under the 80°F germination limit, and where the mean never reaches 75°F, on the hottest normal day. It closes 64 days before the median first 28°F freeze: 50 days to size, plus 14 because fall growth slows, the same count-back as our fall vegetable planting guide.

Across the 31,789 ZIP codes with a 70°F summer mean, the median fall window is 25 days; 4.6% have none and 31.7% have less than two weeks. About 15% of ZIP codes never reach a 70°F mean and need no fall window. Overall, 57.8% of ZIP codes have both a spring and a fall window of at least two weeks.

Boston has the longest window in the table, 65 days: its summer mean never reaches 75°F, so the window opens on the hottest normal day, July 15. In the South the squeeze is real: Nashville has 8 days, Macon 2, and Austin none (6 days short). Table 3 skips Portland and Seattle, which never reach a 70°F mean and can sow lettuce through summer; their last sowing dates are October 17 and September 29.

How published local calendars compare

Seven places have a published window we could convert to dates, nine windows in all. Colorado State’s and Utah State’s spring rules sit inside ours, and so does Maryland’s fall window for Pennsylvania. Clemson’s Piedmont spring window runs 37 days past our heat deadline in Greenville, and UGA’s Macon spring window opens 37 days before ours. Delaware’s August window for head lettuce ends two days before ours opens, because its advice assumes heat-tolerant varieties.⁸

Treat the overlap as the safe core and the edges as judgment calls. Clemson says fall planting is not recommended in the Piedmont and gives September 5 to November 1 on the coast, where our test gives September 25 to November 5.⁷

Mild winters, cool coasts and frost-free ZIP codes

Where winters are mild, lettuce is a winter crop. UF/IFAS says winter is the perfect time to grow lettuce in Florida,¹⁴ and our windows fall in two parts: Houston October 6 to November 2 and January 5 to February 24, Gainesville October 1 to October 22 and February 3 to March 3. The gap between them is closed in our test because a median freeze arrives before a 64-day crop sizes up.

Frost-free ZIP codes have no frost count to use, so look at the months. The normal mean stays under 70°F from November through March in Phoenix (ZIP 85001) and in all twelve months in San Francisco (94103), but only in January and February in Miami (33101). In San Francisco, Portland and Seattle the heat limit never bites; in Phoenix and Miami lettuce is a winter crop.

Types, varieties and ways to stretch the window

Days to maturity set how late you can sow. Illinois Extension gives leaf lettuce 50 to 60 days and butterhead 60 to 70,⁴ the Alabama Cooperative Extension System gives crisphead 70 to 85,¹⁵ and the Almanac says baby greens can be picked at 25 to 40 days.² Maryland rates the whole group at 40 to 80 days,³ and UGA lists lettuce at 60 to 85 for middle Georgia.¹²

• Pick heat-tolerant types for the edges. Maryland recommends slow-bolting or heat-resistant varieties, such as oak-leaf types, to extend the season.³ The Almanac cautions that red leaf varieties are not recommended for hot weather, because the red pigment absorbs more heat.²
• Use primed seed in warm soil. Clemson and Maryland both describe priming as a fix for seed that will not sprout in heat.^7,9
• Sow in small batches. Illinois Extension suggests successive plantings 10 to 14 days apart.⁵
• Protect the late crop. Maryland says row covers or cold frames extend lettuce later into fall, and that some cultivars overwinter from transplants set out around October 15.³

How we calculated these dates

Daily temperatures are NOAA’s monthly normals placed on the 15th of each month and interpolated linearly, for the station nearest each ZIP code.¹ Frost and freeze dates are the median dates for 32°F and 28°F. The day counts and the 40°F, 70°F and 75°F lines are the published rules above, applied to air temperature, not soil. Individual years vary by weeks, so treat each window as a planning range.

Next steps

Look up your own frost dates with our frost date lookup and read what a last frost date means. Lettuce shares its early spring window with carrots, peas and onions, and in cold months winter sowing starts it outdoors in containers. More crops are in our vegetable guides.