You can plant lettuce in Seattle as early as mid-February outdoors, with sowings possible through August for fall harvests. Seattle’s mild, maritime climate gives you a remarkably long lettuce season, roughly nine months of the year, if you time your plantings right. The key is working around two challenges: late-winter cold at one end and summer heat at the other.
Spring Planting: February Through April
Seattle’s average last frost falls between March 21 and 31, but lettuce is one of the most cold-tolerant vegetables you can grow. Seeds germinate in soil temperatures as low as 32°F, though the sweet spot is 60 to 75°F. That means you can direct-sow seeds outdoors starting in mid-February if you’re willing to use a simple row cover or cloche for protection. Without any cover, wait until early to mid-March.
If you want a head start, begin seeds indoors under lights in December through February, then transplant seedlings outside in April. This indoor-to-outdoor pipeline is especially useful for head lettuce and romaine, which take longer to mature than loose-leaf types. Transplants handle the transition well as long as you harden them off for a few days first.
One thing to watch for: lettuce seedlings exposed to temperatures between 40 and 50°F for several consecutive days will begin forming flower buds internally. You won’t see the effect right away, but those plants may bolt faster once warm weather arrives. A layer of frost blanket during cold snaps in March helps avoid this early trigger.
Succession Planting for Steady Harvests
A single planting of lettuce gives you a harvest window of maybe two to three weeks before the heads are past their prime or the leaves turn bitter. To keep lettuce on the table from spring through fall, sow new rounds on a regular schedule. For baby leaf lettuce, plant a fresh batch every 7 days. For full-size heads, every 10 days works well.
Start your succession sowings in March and continue through June. You’ll likely pause in July when daytime temperatures climb, then resume in late July or early August for fall harvests. Keeping a simple calendar or setting phone reminders every week or ten days makes this easy to maintain.
Summer: Managing Heat and Bolting
Seattle summers are mild compared to most of the country, but lettuce still struggles when daytime highs exceed 75°F and nighttime lows stay above 60°F. Under those conditions, plants shift from leaf production to flowering, a process called bolting. The leaves turn bitter and the center stalk shoots upward. Once that starts, the plant is done producing edible greens.
You have a few tools to push through the warm months. First, choose slow-bolt varieties. Romaine and crisphead types are naturally slower to bolt than loose-leaf lettuce. Seed companies also sell cultivars bred specifically for heat resistance, often with names like “Slobolt” or “Summer Bibb.” Second, use shade cloth or plant lettuce on the north side of taller crops like tomatoes or pole beans. Even a few degrees of cooling can buy you extra weeks. Third, keep the soil consistently moist, since dry roots accelerate bolting.
Late Summer Sowing for Fall and Winter
Here’s a detail many Seattle gardeners miss: the best time to plant your winter lettuce garden is midsummer, not fall. Head lettuce and romaine should be sown in July. Leaf lettuce varieties can go in as late as mid-August. Plants need enough warmth and daylight to reach a usable size before the short days of November slow growth to a crawl.
According to the WSU Extension planting calendar, you can seed lettuce for summer harvest through the end of June, then shift your focus to fall and winter crops with July and August sowings. Think of it as two overlapping seasons: one winding down, one getting started.
Overwintering With Simple Protection
Seattle’s winters rarely drop below the mid-20s°F, which means lettuce can survive outdoors with modest protection. The options range from simple to semi-permanent, and all of them work.
- Floating row covers: Sheets of synthetic fabric laid directly over plants. Thicker versions, sold as “frost blankets,” protect down to about 28°F, with heavy-duty materials rated to 20°F. They let rain and air through but can collapse under snow, so brush off any accumulation.
- Hoop houses: Plastic sheeting stretched over arched PVC pipe. These block frost, wind, and heavy rain. They’re inexpensive to build and easy to ventilate on sunny days.
- Cold frames: Essentially mini-greenhouses with rigid glass or plastic lids. A south-facing cold frame collects enough solar heat to keep lettuce growing slowly even in December and January.
All of these require two habits. First, you become the rain: soil under covers doesn’t get natural rainfall, so check moisture regularly and water as needed through the winter. Second, ventilate on sunny days. Even weak winter sun can overheat a closed cold frame or hoop house. Open the cover when the sun is out and close it again before sunset.
Dealing With Slugs
Slugs are the single biggest pest for Seattle lettuce growers. The region’s damp climate is ideal for them, and tender lettuce leaves are their favorite meal. Start with habitat management: clear weeds, tall grass, rocks, and boards near your beds, since slugs shelter in cool, damp hiding spots during the day. Encourage natural predators like birds, garter snakes, frogs, and ground beetles.
Hand-picking slugs in the evening or early morning is surprisingly effective for small gardens. For larger plantings, iron phosphate baits (sold under brand names like Sluggo) are organic-approved and safe around pets and wildlife, unlike older chemical baits that can poison dogs and cats. Scatter the pellets around your lettuce bed according to label directions, and reapply after heavy rain.
Varieties Worth Growing in Seattle
All major lettuce types grow well in western Washington: iceberg, butterhead, romaine (also called cos), green leaf, and red leaf. For spring and fall plantings when bolting isn’t a concern, choose whatever you like to eat. For plantings that will mature into warmer weather, lean toward romaine and crisphead types, which resist bolting longer than loose-leaf varieties.
If you’ve had problems with downy mildew, a common fungal issue in Seattle’s damp conditions, look for resistant cultivars. Varieties like Salinas, Alpine, and Bounty were developed with disease resistance in mind. For winter growing, any cold-hardy leaf lettuce will perform well under cover, and many seed catalogs specifically label overwintering varieties.
A Quick Planting Timeline
- December to February: Start seeds indoors under lights for early spring transplants.
- Mid-February to March: Direct-sow outdoors under row cover or cloches.
- April: Transplant indoor-started seedlings outside. Begin succession sowings every 7 to 10 days.
- May to June: Continue succession sowings. Switch to bolt-resistant varieties as temperatures rise.
- July: Sow head lettuce and romaine for fall harvest. Use shade cloth for any remaining summer lettuce.
- Mid-August: Last call for sowing leaf lettuce for fall and winter harvests.
- September to November: Harvest fall crops. Put protective covers in place before the first hard frost.
- December to February: Harvest overwintered lettuce from under covers. The cycle starts again.