How to Grow Lettuce: Beating the Bolt and the Bitterness

Lettuce turns bitter and runs to seed in heat. Sowing windows, cut-and-come-again, shade in summer, and why germination fails in warm soil.

By Zakaria September 20, 2026 4 min read Save to Pinterest

A young loose-leaf lettuce plant with wavy bright green leaves growing in dark soil — Photo: GT1976, CC BY-SA 4.0, via Wikimedia Commons

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Lettuce is easy for about eight weeks of the year and awkward for the rest. Everything difficult about it — bitterness, bolting, seed that refuses to germinate — is the same problem: heat.

The short answer

Lettuce is a cool-season crop that bolts and turns bitter in heat, so sow in early spring and again from late summer, every two to three weeks, rather than through midsummer. Seed enters thermodormancy above about 80°F and will not germinate, which is solved by sowing in late afternoon, watering the drill first, shading it, or starting indoors. It needs only four to six hours of sun and benefits from afternoon shade in summer. Loose-leaf types can be cut an inch above the crown and will regrow three or four times; hearting types cannot.

Cool season. Spring and autumn, not midsummer
Bitter means bolted — and it does not come back
Seed will not germinate above ~80°F. Sow late afternoon
4–6 hours of sun is enough. Afternoon shade helps in summer
Cut an inch above the crown for three or four harvests

Timing

Sowing windows

Season	When	Notes
Spring	From 4 weeks before last frost	Successional, every 2–3 weeks
Summer	Only with shade and bolt-resistant varieties	Hard work; often not worth it
Late summer–autumn	8–10 weeks before first frost	The best crop of the year
Winter, zones 8–10	Autumn sowing	Grows right through

Sow a little and often. A single large sowing gives a glut followed by a wall of bolted plants; a short row every two or three weeks gives a steady supply.

Germination in warm weather

Lettuce seed has a built-in refusal called thermodormancy: above roughly 80°F it will not germinate at all, because a seedling emerging into that heat would not survive.

Working around it:

Sow in the late afternoon, so the critical first hours happen overnight in the cool
Water the drill thoroughly before sowing, not just after
Shade the row — a board, shade cloth, or the shadow of a taller crop
Chill the seed in the fridge for a couple of days first
Start indoors somewhere cool and transplant
Sow shallowly. Lettuce needs light to germinate; barely cover it

Growing it

Conditions


Sun	4–6 hours. Afternoon shade is a bonus in summer
Soil	Moisture-retentive, rich, well drained
Water	Consistent. Drought stress triggers bolting
Feed	Light nitrogen. It is a leaf crop, but too much invites aphids
Spacing	6–8 in for hearting types; thick for cut-and-come-again
Depth	Shallow roots — 6 in of container is enough
Mulch	Yes. Keeps the roots cool, which delays bolting

Thin ruthlessly for hearting varieties — crowded plants make small hearts and bolt earlier. Thinnings are the first salad of the season.

Bolting, and the bitterness

When a lettuce switches from making leaves to making seed, it elongates a central stem and floods the leaves with a milky latex. That latex is the bitterness, and it is irreversible.

What triggers it

Trigger	What to do
Heat	Shade cloth, afternoon shade, mulch, bolt-resistant varieties
Drought stress	Water consistently; never let it dry out
Age	Harvest sooner. Do not leave plants standing
Long days	Time sowings so maturity falls outside midsummer
Transplant shock	Handle roots gently; water in well

Pick in the morning

Latex concentration rises through the day, so leaves cut in the early morning are measurably sweeter than the same leaves cut in the afternoon.

It is the cheapest improvement available, and it is the reason market-garden lettuce is harvested before breakfast.

Cut-and-come-again

The method that gets the most out of a small space.

Sow loose-leaf varieties thickly in a band rather than spaced individually
Let them reach 4 to 6 inches
Cut the whole patch about an inch above the crown with scissors
Water and feed lightly
Regrowth in 2 to 3 weeks. Expect three or four cuts before quality falls off

It only works on loose-leaf and some romaine types. Iceberg, butterhead and other hearting varieties form a single head from one growing point and do not regrow once cut.

Types, and what each is for

Choosing

Type	Cut-and-come-again?	Notes
Loose-leaf (Salad Bowl, Lollo Rossa)	Yes	Fastest, easiest, most bolt-tolerant
Romaine / cos	Partly	Upright, crisp, reasonably heat-tolerant
Butterhead (Buttercrunch, Tom Thumb)	No	Soft heads; Buttercrunch is unusually bolt-resistant
Crisphead / iceberg	No	Longest season, fussiest, most likely to disappoint
Batavian / summer crisp	Partly	The best summer choice — genuinely slow to bolt

For a summer sowing, Batavian types and Buttercrunch are the ones that actually work. Iceberg in July is a lesson rather than a crop.

Problems

Bitter, tall, milky sap — bolted. Pull it and resow
Seed never came up in summer — thermodormancy. See above
Ragged holes, slime trails — slugs. Lettuce is their favourite thing in the garden
Sticky leaves, curled growth — aphids, often inside the heart where spraying cannot reach
Collapsed at soil level — damping off or grey mould, from sowing too thickly into cold wet soil
Pale, slow, yellowing — usually hungry, or too little light

Common questions

When should I plant lettuce?

Lettuce is a cool-season crop, so the productive windows are early spring and late summer into autumn rather than midsummer. Sow from about four weeks before the last frost, then every two to three weeks until daytime temperatures reach the mid-seventies, and start again eight to ten weeks before the first autumn frost. In mild-winter regions of zones 8 to 10 lettuce grows right through winter, which is when it is at its best.

Why is my lettuce bitter?

Heat and bolting. When a lettuce plant switches from leaf production to flowering it sends up a central stem and floods the leaves with a milky latex that tastes bitter, and the change is irreversible — no amount of watering brings the flavour back. Heat triggers it, as does drought stress and simply leaving the plant too long. Pick in the morning when leaves are coolest, harvest before the plant elongates, and use bolt-resistant varieties for summer sowings.

Why won't my lettuce seed germinate in summer?

Lettuce seed enters thermodormancy above roughly 80°F — a deliberate refusal to germinate in conditions that would kill the seedling. Sow in the late afternoon so the critical first hours fall in the cool of the night, water the drill thoroughly before sowing, shade the row, or start seed indoors somewhere cool and transplant. Chilling seed in a fridge for a couple of days before sowing also helps break the dormancy.

What is cut-and-come-again lettuce?

A method rather than a variety: sow loose-leaf lettuce thickly, then harvest by cutting the leaves about an inch above the crown rather than pulling the plant. The growing point survives and regrows, giving three or four cuts from one sowing over several weeks. It only works with loose-leaf and some romaine types, because hearting varieties such as iceberg and butterhead form a single head and do not regrow once cut.

How much sun does lettuce need?

Less than most vegetables, which is useful. Four to six hours is plenty, and in summer afternoon shade is an advantage rather than a compromise — it delays bolting and keeps the leaves sweeter. Lettuce is one of the few crops that genuinely performs in a part-shade bed, interplanted between taller crops, or under shade cloth during the hottest weeks of the year.

Can I grow lettuce in containers?

Very well, and shallow ones at that, since the roots are fine and near the surface — six inches of depth is enough. A wide shallow container suits it better than a deep narrow one, and containers make it easy to move the crop into afternoon shade when the weather turns hot. Keep the compost consistently moist, because a pot dries faster than a bed and drought stress is one of the things that triggers bolting.

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A loose-leaf lettuce plant growing in bare soil

Growing Guides · Sep 1, 2026