Arbor

How to Grow Lettuce

Updated July 2026

Lettuce grows best when daytime temperatures stay between 55–65°F and nights drop near 50°F. Above 75°F most varieties begin forming a flower stalk and the leaves turn bitter — that window is the whole game. Get your timing right, water every 2–3 days to keep the shallow roots moist, and a looseleaf crop reaches harvest in about 45 days from transplant.

How it works

Lettuce is a cool-season crop whose quality is temperature-driven above everything else. The University of Minnesota Extension reports that temperatures above 75°F trigger bolting in most varieties — a process where the plant shifts energy to flowering, producing elongated, bitter leaves. Long days and high light intensity accelerate this response alongside heat.

Bolting is a timing problem, not a care failure. The fix is sowing early enough in spring to complete the crop before heat arrives, then starting a second planting in midsummer for fall harvest. Looseleaf types like Slobolt and Red Sails tolerate brief 80–85°F daytime highs better than head types, especially when nights stay cool and soil moisture is consistent. Iceberg needs the longest uninterrupted cool window and is the least forgiving in warm climates.

Tipburn — browning of leaf edges or inner leaves — gets blamed on calcium deficiency, and Clemson Extension does name calcium as the root cause, but NC State Extension ties it to water availability and growth rate. Both point to inconsistent watering as the practical driver: when soil dries out, calcium can’t move fast enough through the plant. Adding calcium to the soil rarely fixes it; consistent moisture does.

What to do

Choose the right type for your window. Looseleaf lettuce (Black Seeded Simpson, Red Sails, Salad Bowl) matures fastest and lets you harvest individual leaves over several weeks without pulling the plant. Butterhead (Buttercrunch, Bibb) takes slightly longer and forms soft, loose heads. Romaine needs 8 inches of space and is ready to harvest when the base reaches about 6–8 inches tall. Iceberg requires 12–15 inches between plants and needs the longest cool stretch — 55 or more days without serious heat. For hot climates or short springs, start with looseleaf.

Time your planting. Direct sow seeds 1/4 to 1/2 inch deep, roughly 1 inch apart in rows 12–18 inches apart, about 2 to 4 weeks before your last frost date — lettuce tolerates light frost down to 28°F. Seeds germinate best at 55–65°F soil temperature; germination drops sharply above 80°F. For transplants, start seeds indoors 4 weeks before your intended outdoor date, then move plants outside about 4 weeks before last frost. Transplants reach harvest 2–3 weeks earlier than direct-seeded plants of the same variety. For a fall crop, count back 50–75 days from your first expected fall frost and plant then; University of Minnesota Extension recommends starting seeds indoors in July for August transplanting in northern climates.

Thin and space correctly. Once seedlings reach 1–2 inches tall, thin looseleaf and butterhead to 8 inches apart. Iceberg needs 12 inches minimum. Thin progressively — pull every other plant as baby-leaf harvests.

Water consistently and often. Lettuce has shallow roots concentrated in the top 6–12 inches of soil. Water every 2–3 days — frequent light watering prevents both tipburn and bolting more reliably than less frequent deep soaking. Aim for at least 1 inch per week in temperate climates; Utah State Extension recommends 1–2 inches in drier or hotter conditions. Above 80°F, shorten the interval. Water in the morning so foliage dries before evening, and use drip over overhead sprinklers to reduce disease splash.

Fertilize with nitrogen, in stages. Work a balanced fertilizer — 5-10-10 at 3 pounds per 100 square feet — into the bed before planting, along with compost. At thinning or once plants reach 4 inches tall, side-dress with 1/4 cup of a nitrogen-based fertilizer (21-0-0) per 10-foot row, per Utah State University Extension. Heavy nitrogen worsens tipburn and reduces head quality in iceberg.

Extend the season with shade and covers. In warm weather, afternoon shade from taller crops — tomatoes, broccoli, Brussels sprouts — delays bolting. Floating row covers made from spun-bonded polypropylene add about 4°F of frost protection, effective down to 28°F, and protect seedlings from flea beetles in early spring.

Arbor’s watering schedule for lettuce defaults to every 2–3 days off your forecast, and shortens automatically when temperatures climb above 80°F.

Harvest before the plant bolts. Begin harvesting outer looseleaf leaves when plants reach 5–6 inches tall, or cut the whole plant at soil level — it regrows in 2–3 weeks with consistent water. For head types: pick iceberg when the head is compact and firm, butterhead when leaves cup inward, romaine when the base reaches 4 inches wide and 6–8 inches tall. The moment the center begins elongating on any type, harvest immediately. That stalk will not revert.

Succession plant every 2 weeks. A single sowing peaks and declines within a few weeks. Staggering plantings every 10–14 days through spring, then again in late summer for fall, gives a continuous supply without gluts.

Zone and season notes

Northern tier (zones 3–4, Minnesota and similar). Direct seed as soon as soil is workable in April. For fall, start seeds indoors in July and transplant in August. Looseleaf and early butterhead are the practical choices when frost cuts the season short.

Mountain West (zones 5–7, Utah and similar). Plan on 1–2 inches of water per week — dry Western air pulls moisture faster than humid climates, and bolting thresholds arrive quickly when irrigation lapses. Start fall planting 50–75 days before your first expected fall frost.

Mid-Atlantic (zones 6–7, Maryland and similar). University of Maryland Extension recommends planting cold-hardy varieties — Winter Density, Brune D’Hiver, Arctic King — around October 15 for overwintering under row covers.

Southeast and Gulf Coast (zones 7–9). Clemson Extension puts South Carolina’s spring window from February 1 through April 15. Fall is often the better season: the window runs September through November, and University of Minnesota Extension notes that cooler weather produces noticeably sweeter flavor. In humid conditions, prefer drip over overhead watering and space plants at the wider end of the range to improve airflow and reduce fungal pressure.

Mild-winter climates (zones 9–11, California and similar). Fall and winter are the primary lettuce season. Afternoon shade extends the spring window a few weeks; looseleaf heat-tolerant varieties like Slobolt and Nevada are the standard tools once daytime highs regularly reach 70°F.

All regions. Stop direct sowing 50–60 days before the expected onset of sustained heat. For fall, looseleaf needs at least 45 days from planting to harvest; head types need 60–80 days.

Sources

  • University of Maryland Extension — Growing Lettuce in a Home Garden — extension.umd.edu/resource/growing-lettuce-home-garden
  • Utah State University Extension — How to Grow Lettuce in Your Garden — extension.usu.edu/yardandgarden/research/lettuce-in-the-garden
  • University of Minnesota Extension — Growing Lettuce, Endive, and Radicchio — extension.umn.edu/vegetables/growing-lettuce-endive-and-radicchio
  • Clemson HGIC — Lettuce — hgic.clemson.edu/factsheet/lettuce/
  • NC State Extension — Lettuce Production in North Carolina — content.ces.ncsu.edu/lettuce