Vegetable · Asteraceae
Lettuce
Lactuca sativa
Grown cool, moist, and quick, lettuce spreads a low rosette of crisp, tender leaves in about a month.
Full sun
Every 2–3 days
55–64°F · 13–18°C
45–75 days
Overview
Lettuce grows as a low rosette of broad, tender leaves that races from seed to a cuttable plant in as little as 45 days. It belongs to the daisy family and lives as a cool-season annual, its leaves sweetest through the mild weeks of spring and fall. Break a stem and a thin milky sap beads at the cut, the same white latex that runs bitter once the plant heats up.
The leaves themselves take many shapes. Loose-leaf types spread open, frilled or ruffled rosettes of green or bronze-red blades, upright romaines stack stiff, ribbed leaves into a tall column, and butterheads fold soft, cupped leaves into a loose head. Whatever the form, the plant keeps low and compact, its rosette rarely rising past 12 inches (30 cm) before harvest.
Heat rewrites the plant's shape. A thick stalk bolts straight up from the flat center, the once-sweet leaves turn coarse and bitter, and the milky sap sharpens. Kept in cool weather with steady moisture and good light, though, the leaves stay crisp, smooth, and sweet right to the cut.
Care
The short version: full sun with a little afternoon shade in the heat, evenly moist soil, rich well-drained ground near a pH of 6.0 to 6.7, and cool weather between 55°F and 64°F (13°C to 18°C) that keeps the crisp leaves sweet.
Light
Lettuce colors up on full sun in cool weather, its leaves crisp and firm, but it takes partial shade in stride and welcomes it as the heat builds. A spot with morning sun and afternoon shade keeps the blades tender and holds the center down before it can bolt.
Water
Keep the soil evenly moist at all times, watering every 2 to 3 days and deeper in the heat. The roots run shallow beneath the rosette, so a dry spell stresses the plant fast and edges the leaves toward bitter. Water deeply to about 6 inches and never let the bed dry out.
Soil
Root it in loamy, rich, well-drained ground worked full of organic matter. A pH between 6.0 and 6.7 suits it, and soil that stays moist without turning soggy fills the leaves out plump and crisp.
Temperature
This cool-season crop keeps its leaves sweet and firm between 55°F and 64°F (13°C to 18°C). Past about 75°F the center shoots up and bolts, so time the sowings for the mild shoulders of the year.
Humidity
Ordinary outdoor humidity is plenty, and there is no number to chase. Steady soil moisture is what fills the leaves out, since dry roots, not dry air, are what turn the blades bitter.
Feeding
Work a 5-10-10 fertilizer in before planting, then sidedress once with calcium nitrate as the leaves expand. That second feed swells the leafy growth and supplies the calcium whose absence browns the leaf edges in tipburn.
Pruning
No real pruning is needed. Pick the outer blades as they broaden and the center keeps pushing out fresh leaves, then pull the plant once it bolts, since the leaves only coarsen and sour from there.
Size & spacing
Lettuce spreads a low rosette 6 to 12 inches (15 to 30 cm) tall and about as wide. Give each plant 6 to 12 inches (15 to 30 cm) of room so the leaves can broaden fully and air can move between the rosettes.
When to plant
Lettuce spreads its tender leaves in the cool ends of the year, not high summer. Sow the first rosettes in early spring once the soil can be worked, sow again in late summer for a fall crop, and skip the hottest weeks between, when the center only wants to shoot up and bolt.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 4-6 weeks before the last spring frost
- Plant: 2-4 weeks before the last spring frost; sow again in late summer for a fall crop
- Harvest: Spring and fall harvest (cool season)
Hardiness
USDA hardiness zones: 2–11
Temperature: down to -46°C
Troubleshooting
Most lettuce trouble reads straight off the leaves, in a browned edge, a chewed hole, or a puckered blade, and nearly all of it traces back to heat, uneven water, or a feeding pest. Read the leaf closely and the cause is usually plain. Match what you see below, then act before the whole rosette turns.
A tall stalk climbs from the core and the leaves sour
This is bolting, when the low rosette pushes a thick stalk straight up from its center and trades leaf for seed once heat above 75°F (24°C) and longer days signal the season's close. Snap a leaf then and a milky white sap beads at the break, and the sweetness is gone for good. Cut the moment the middle lifts, cast afternoon shade over the plants in a hot spell, and lean on slow-to-bolt varieties.
Fix:
- Harvest promptly before the plant fully bolts
- Switch to heat-tolerant, bolt-resistant cultivars
- Provide afternoon shade during hot spells
Puckered leaves glazed with a sticky sheen
This is the work of aphids, pinhead-sized soft-bodied insects clustered along the leaf undersides and glazing them with a sticky, glistening honeydew. The fresh leaves crimp and pucker where the insects have fed. A hard jet of water strips them off, insecticidal soap catches the clingers, and ladybugs and other predators pick off the rest.
Fix:
- Dislodge with a strong spray of water
- Apply insecticidal soap
Dry brown edges rim the young inner leaves
This is tipburn, a thin band of brown, brittle, dead tissue that rims the young leaves deep in the heart while the outer ones stay green. It is a calcium shortfall in that fast-growing core, not the mark of a pest. When warm weather and uneven watering push the growth, the inner leaves cannot pull in enough calcium and their margins die. Even soil moisture and light nitrogen keep the growth in check.
Fix:
- Maintain even soil moisture
- Avoid excessive nitrogen that pushes rapid growth
Torn holes and glistening streaks across the blades
This is the calling card of slugs and snails, ragged chewed holes with smooth-edged rims and dried silvery streaks of mucus laced across the leaf blades. They feed under cover of dark, and the damage runs worst in damp weather. Iron phosphate bait, hand-picking by torchlight, and clearing the moist mulch and debris they shelter in bring them down. Morning watering leaves the surface dry by nightfall, which they shun.
Fix:
- Apply iron phosphate bait
- Hand-pick at night
- Reduce damp mulch and debris near plants
Toxicity
Lettuce is one of the safest plants you can grow. Every part, from the crisp green blades to the milky sap at a cut stem, is non-toxic to people and to cats, dogs, rabbits, horses, livestock, and birds. The one small quirk is that milky sap, which may leave a mild rash on very sensitive skin and nothing worse.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Lettuce is safe for cats, and a leaf nibbled to a crescent does no harm. Most cats pass the crisp green blades by, though a curious one can chew them freely.
Dogs None
Dogs eat lettuce without trouble. Because the leaves run so watery, a large helping can loosen the stool, so small pieces of plain washed leaf are the sensible portion.
Horses None
Horses take lettuce well as an occasional treat. The broad leaves tear easily into ribbons, and a modest portion is plenty, as with any fresh green.
Rabbits None
Rabbits favor the crisp, deep-green outer blades over the pale, watery hearts folded at the center. The leaves are served washed, alongside their usual hay.
Livestock None
Goats, sheep, and backyard stock graze lettuce safely. Even a bolted plant, its stalk risen and its leaves gone bitter, is harmless, if less tempting to them.
Birds None
Chickens and pet birds peck at fresh lettuce leaves with no risk, tearing small beakfuls from the blades. The darker, leafier types give them more crisp green to work at than the pale, watery crispheads.
People None
Lettuce is a salad staple eaten raw or cooked and safe for everyone. The milky sap that beads at a cut stem may rarely leave a mild rash on very sensitive skin, and nothing worse.
The milky sap may rarely cause mild contact dermatitis in sensitive individuals.
Varieties
Hundreds of lettuces fill the leaf, romaine, and butterhead groups, differing in leaf shape, color, and how tightly they gather. A handful stand out season after season, and these are the ones worth knowing by their look.
Parris Island Cos
An upright romaine of tall, crisp green leaves that stand in a stiff column and shrug off disease.
Tom Thumb
A miniature butterhead whose soft leaves fold into one tidy single-serving head in about 70 days.
Simpson Elite
A fast-growing green leaf type with ruffled, loosely gathered blades that resists bolting longer than most.
Red Sails
A loose-leaf variety washed bronze-red at the frilled leaf edges, prized for that color and its slow turn to bolting.
Defender
A green romaine of tall, ribbed leaves bred to resist downy mildew and other common diseases.
How to propagate
Lettuce is about as simple as growing gets, and a single packet of small, slender seed keeps fresh rosettes rising for months when it is sown in waves.
SeedEasy
Spring and late summer; sow in succession every 2-3 weeks for a continuous harvest · 7-14 days to germinate
Lettuce grows readily from small, slender seed pressed just under the surface, about a quarter inch deep, since it needs light and cool soil to break dormancy. Thin green cotyledons unfurl and push up in 7 to 14 days, followed by the first true leaves. Pressing a fresh pinch of seed into the row every 2 to 3 weeks through spring and again in late summer keeps young rosettes rising in waves rather than all at once.
Myths
Bitter lettuce is spoiled or rotten.
Bitterness is the plant's normal response to heat as it bolts, not rot, and the milky sap that carries it beads clear at a broken leaf. The leaves stay safe, only sharp on the tongue. Grow it cool and cut it early and the sweetness holds.
Lettuce needs full hot sun all day to grow well.
It is a cool-season crop, and unbroken all-day sun drives its center to shoot up and bolt. A little afternoon shade in the heat keeps the leaves tender, though the plant still wants plenty of light the rest of the day.