How to Grow Lettuce

Lettuce is a cool-weather crop that tolerates light frost and sulks in heat. Illinois Extension puts its sweet spot at an average daily temperature of 60 to 70°F, and Utah State says it grows best when temperatures stay below 75°F. Above that, growth slows, leaves turn bitter and the plant starts building a seed stalk. The goal is to keep it growing fast and steadily in cool weather, then pick it before the heat arrives.

Pick the right type for your season

The main garden types differ a lot in how forgiving they are.

Leaf (loose-leaf) lettuce is the most widely adapted type and the easiest. It never forms a head, so you can start picking young leaves within weeks and keep going until the weather turns hot. NC State gives about 50 to 60 days from seed to full size, or 30 to 45 days from transplants.

Butterhead (Bibb and Boston types) forms a small, loose head of soft, sweet leaves. Illinois puts heads at 4 to 8 ounces after 60 to 70 days. Maryland warns that Bibb turns bitter in high summer heat.

Romaine (cos) grows into an upright, elongated head. Maryland calls it relatively easy to grow and says gardeners grow it less often than it deserves.

Crisphead (iceberg) is the supermarket type and the hardest in a home garden. It needs a long, cool season to form a firm head, and NC State gives 70 to 80 days from seed. An early heat wave before the heads are mature almost always ruins the crop, according to Illinois.

Sources don’t fully agree on which type handles heat best. NC State ranks leaf and butterhead as the most heat tolerant, then romaine, with head lettuce last. Colorado State says that along the Front Range, romaine holds up better than both leaf and head lettuce when the weather warms. Everyone agrees crisphead is the least tolerant.

When to plant

Lettuce goes in early. Utah State says to sow seed 2 to 3 weeks before the last spring frost, while NC State says 2 weeks. Illinois and Maryland go further and say leaf and butterhead lettuce can be sown as soon as the soil is dry enough to rake. Start from the dates for your zone above, then check the soil.

Utah State says lettuce can be sown once the soil reaches 40°F and germinates best at 55 to 65°F. UW-Madison’s soil chart is a little warmer, with a 45°F minimum and a 75°F optimum. Warm soil is a problem too: Utah State notes that soil above 80°F reduces germination. That is why midsummer sowings often fail.

Transplants give you an earlier harvest, and for crisphead they are close to essential outside regions with long, cool springs. NC State starts seed indoors 6 to 8 weeks before the last frost. Utah State and UGA both allow 5 to 6 weeks. Utah State says a transplant is ready when it has 4 to 6 mature leaves and a well-developed root system. UGA adds that plants grown in an unheated cold frame can take 10 to 12 weeks. Harden transplants outdoors for 4 to 5 days first (UGA’s figure) and set them out around the last frost date.

For a steady supply, sow a short row every 2 weeks (NC State) or every 10 to 14 days (Illinois). Illinois also advises finishing spring planting at least a month before your area’s really hot weather begins.

Fall lettuce

Fall can be the better season, because plants mature as the weather cools instead of heating up. That is especially true for crisphead. Utah State’s method is to choose early varieties and count back 50 to 75 days from the harvest date you want, aiming to finish 1 to 2 weeks before the first fall frost. NC State’s simpler rule is to sow about 3 months before the first frost. The fall dates for your zone above follow the same logic. Getting seed to sprout in late-summer heat is the hard part. Sow in a shaded spot, keep the seedbed moist, and move seedlings to the garden once they are established.

Sowing: shallow, fine and moist

Lettuce seed is tiny, and UF/IFAS notes that it needs light to germinate. Illinois says this is true especially of white-seeded varieties. Depth guidance varies a little: Utah State and Illinois say 1/4 to 1/2 inch, NC State 1/4 to 3/8 inch, and UGA 1/8 to 1/4 inch. For light-sensitive seed, the shallow end is safer. Rake the soil fine, press the seed in, and firm it lightly so it touches moist soil. On heavy clay that crusts, Clemson suggests covering the seed with potting mix instead of garden soil.

Keep the seedbed moist but not soggy until seedlings are up. UGA says to water often for the first 2 weeks. When germination fails, Illinois blames dry soil or old seed. Lettuce seed doesn’t keep well, so buy fresh seed each spring and store any seed saved for fall in a sealed container in the refrigerator.

Spacing and thinning

Thin when seedlings have 3 or 4 true leaves (Utah State). Final spacing depends on the type. Illinois thins leaf lettuce to 4 inches and romaine or butterhead to 6 to 8 inches, and sets crisphead transplants 10 to 12 inches apart. Utah State gives 8 to 12 inches for head lettuce, and Maryland gives crisphead 12 to 15 inches. Rows run 12 to 18 inches apart in most sources. Eat the thinnings or replant them with roots attached (Utah State).

Dense planting has a benefit: the leaves shade the soil and crowd out weeds. Lettuce competes poorly with weeds when young, so Utah State and Clemson both stress early weed control. Hoe shallowly, because the roots are close to the surface and cutting them stalls growth.

Soil and feeding

Lettuce wants fertile, well-drained soil with plenty of organic matter. Clemson and UGA recommend a pH of 6.0 to 6.5, and NC State gives 6 to 6.7. A soil test is the best guide. Without one, Clemson suggests 3 pounds of 5-10-10 per 100 square feet before planting.

Lettuce responds well to nitrogen. Utah State sidedresses with 1/4 cup of 21-0-0 per 10 feet of row about 4 weeks after transplanting or thinning, placed beside the row and watered in. Clemson prefers calcium nitrate at 2 pounds per 100 feet of row, and it advises against ammonium-based nitrogen because it can contribute to tipburn. Clemson adds that sandy soil or heavy rain may call for more frequent sidedressing.

Watering: the real secret

Utah State recommends 1 to 2 inches of water a week, adjusted for soil and temperature. The amount matters less than keeping it steady. When the soil swings between wet and dry, leaves turn tough and bitter, heads form slowly, and tipburn shows up.

Sources differ on how to water. Illinois and Maryland favor frequent light watering to keep growth rapid. Clemson warns that light sprinklings encourage shallow roots and says to wet the soil to a depth of 6 inches each time. Both approaches aim for constant moisture in the root zone.

Drip lines or soaker hoses keep the leaves dry, which cuts down on rot. If you water overhead, do it in the morning so the foliage dries before night (Maryland, Clemson). Overwatering heavy soil invites disease, soft growth and scorched leaf edges (Illinois). An organic mulch of straw or grass clippings holds moisture and keeps the soil cooler as spring warms.

Why lettuce bolts, and how to delay it

Bolting is when the plant sends up a seed stalk. It is triggered by a combination of long days, warm temperatures and age, and dry soil speeds it up (Illinois, NC State). NC State says temperatures of 70 to 80°F together with dry soil can set it off. Once the stalk starts, leaves turn bitter and leaf production stops.

You can’t stop day length, but you can delay bolting:

• Time it right. Finish spring crops before the first hot spell.
• Choose slow-bolting varieties for later sowings. Maryland mentions oakleaf types.
• Add shade. Maryland suggests planting late spring lettuce where sweet corn, staked tomatoes or pole beans will shade it in the afternoon, or using shade cloth in summer. For summer lettuce, NC State suggests 3 to 4 hours of sun a day and shade the rest of the time.
• Keep watering. Dry soil is a bolting trigger.

When you see the center stretching upward, harvest the whole plant at once and refrigerate it. Mildly bitter leaves improve if you wash them and chill them for a day or two (Illinois, Utah State).

Regional differences

Cold northern states and high elevations. Spring is short and can swing from frost to heat in a week, so transplants and fast leaf types pay off. Colorado State notes that spring temperature swings make cool-season crops hard to grow along the Front Range. In its trials, the lettuce ‘Sierra’ did not bolt. Fall crops usually taste better because they mature into cooling weather. Row covers and cold frames stretch the harvest into late fall.

Pacific Northwest. West of the Cascades, the cool marine climate suits lettuce well. WSU Extension in Skagit County says lettuce can be direct-seeded by March or a week or two before the last frost. It names ‘Gabriella’ and ‘Simpson Elite’ among varieties that do well in the Northwest climate. Damp conditions favor slugs, so watch for them.

The humid South. Heat and humidity are the problems here, not cold. UGA advises Georgia gardeners to skip head lettuce entirely and grow leaf, romaine and Bibb types. Clemson says head lettuce is generally harder than leaf lettuce in the South. Clemson also lists fall lettuce as not recommended in the South Carolina Piedmont, while the Coastal Plain gets both a spring and a fall crop. Clemson says excellent lettuce can be grown all winter in South Carolina if you cover it on the coldest nights. Illinois notes that leaf rots are worst in hot or wet seasons, so give beds good drainage and airflow.

Warm-winter areas (zones 9 to 11). In Florida, along the Gulf Coast, in south Texas and in the Arizona low desert, lettuce is a fall-through-late-winter crop. UF/IFAS says leaf types grow well in Florida, but crisphead only succeeds in the coolest months. The Maricopa County calendar for the Phoenix area starts seeding in late summer and continues through winter. The months for these areas are in the dates for your zone above.

The arid West. Utah State notes that most Utah soils suit lettuce. Its advice for dry climates is drip irrigation to save water, mulch to hold moisture, and plastic mulch for an early spring crop. Water needs rise with temperature and in fast-draining soil, so check moisture often.

Overwintering and season extension

Floating row covers and cold frames carry fall lettuce later into the season (Maryland). Clemson says a light to medium spunbonded row cover gives about 4 degrees of frost protection down to 28°F. In Maryland, healthy three-week-old transplants set out around mid-October can root in, survive the winter with protection, and resume growth for an early spring harvest. Maryland lists ‘Black Seeded Simpson’, ‘Waldmann’s Dark Green’, ‘Salad Bowl’, ‘Winter Density’, ‘Brune d’Hiver’, ‘Winter Marvel’ and ‘Arctic King’ for this.

Varieties recommended by extension services

Extension services recommend different varieties for their own climates. Use the list closest to your region:

• Utah (Utah State): crisphead ‘Summertime’, ‘Salinas’, ‘Great Lakes’; butterhead ‘Buttercrunch’, ‘Esmeralda’; leaf ‘Red Sails’, ‘Oakleaf’, ‘Salad Bowl’, ‘Black Seeded Simpson’.
• North Carolina (NC State): head strains ‘Ithaca’, ‘Pennlake’ and ‘Salinas’ grow well in the state; ‘Jericho’ romaine is heat tolerant; ‘New Red Fire’ leaf lettuce resists heat and bolting; ‘Buttercrunch’ is bolt resistant.
• South Carolina (Clemson): leaf ‘Slobolt’, ‘Green Ice’, ‘New Red Fire’, ‘Red Sails’; Boston ‘Buttercrunch’, ‘Esmeralda’; romaine ‘Parris Island Cos’, ‘Defender’, ‘Sunbelt’.
• Georgia (UGA): romaine ‘Green Towers’, ‘Super Jericho’; leaf ‘Slobolt’, ‘Royal Oak Leaf’; Bibb ‘Little Gem’, ‘Summer Bibb’.
• Florida (UF/IFAS): leaf ‘Salad Bowl’, ‘Red Sails’, ‘New Red Fire’; butterhead ‘Buttercrunch’, ‘Bibb’; romaine ‘Parris Island Cos’, ‘Outredgeous’; crisphead ‘Great Lakes’ in the coolest months only.
• Texas (Texas A&M): crisphead ‘Mission’; looseleaf ‘Red Sails’, ‘Salad Bowl’; butterhead ‘Buttercrunch’, ‘Esmeralda’, ‘Summer Bibb’; romaine ‘Paris Island’, ‘Winter Density’.

Common problems and fixes

• Tipburn (brown, dead leaf edges, often on inner leaves). Clemson says it is a calcium problem driven mainly by drought and uneven watering, with heat, wind, rapid growth and ammonium-based fertilizer adding to it. Water evenly and choose resistant varieties. Illinois says to trim the brown edges and eat the rest of the leaf.
• Aphids cluster under the leaves and make them crinkle and curl. Knock them off with a strong spray of water or use insecticidal soap.
• Slugs and snails chew ragged holes in damp weather. Use traps, avoid keeping the bed wetter than needed, or use an iron phosphate bait (Clemson). Row covers also reduce slug feeding (Maryland).
• Flea beetles pepper seedlings with tiny holes. Cover new plantings with floating row cover.
• Caterpillars such as loopers and armyworms. NC State notes pest pressure is much heavier on summer and fall crops than on spring ones.
• Damping-off kills seedlings at the soil line. Mildews, gray mold, bottom rot and Sclerotinia drop attack older plants. Good drainage, airflow, morning watering and rotating the bed each year help.

Harvest and storage

Leaf lettuce can be picked as soon as plants are 5 to 6 inches tall (Maryland). Take the outer leaves first so the center keeps growing, or cut every other plant at ground level to give the rest more room. For cut-and-come-again greens, Maryland suggests shearing a thickly sown bed at 6 to 10 inches. It will be ready to cut again in 2 to 3 weeks if you keep it watered and fed. Butterhead is ready when the leaves begin to cup into a loose head. Romaine is ready when the leaves overlap into a fairly tight head about 6 to 8 inches tall. Crisphead is ready when the head is firm. Utah State estimates a 10-foot row yields 4 to 6 pounds and suggests planting 5 to 10 feet of row per person.

Harvest when the leaves are dry, then refrigerate them in a bag. Lettuce keeps best near 32°F with high humidity. Maryland says leaf and Bibb lettuce can last up to four weeks if bagged dry, and crisphead about two. Utah State gives 1 to 2 weeks, and UGA plans on about a week in a home refrigerator. Keep lettuce away from apples, pears and bananas, which give off ethylene gas that causes brown spots.

Some gardeners grow lettuce with taller crops such as tomatoes, broccoli, Brussels sprouts or pole beans. That is a space-saving and shading arrangement, not a proven companion effect.