Lettuce · indoors

Growing lettuce indoors all year

It works, and the limiting factor is almost never the pot or the feed. It is how many hours of real light the spot gets in December.

The honest constraint

Lettuce needs roughly six hours of direct light a day to grow rather than merely survive. In a temperate winter, a windowsill may deliver two or three. That is the whole problem, and it is why indoor lettuce succeeds in spring and autumn and stalls in midwinter unless you add a lamp. A cheap 20–30 W LED panel for 12 hours a day closes the gap; nothing else about the setup needs to change.

Temperature matters more than people expect

Aim for 15–21 °C. Above about 24 °C lettuce stops making leaves and starts thinking about flowering, which is why a warm kitchen in February is worse than a cool spare room. Move the container rather than the thermostat.

Containers and compost

Depth: 15 cm is plenty. Lettuce roots are shallow and wide.
Drainage: holes, always. Lettuce tolerates wet far worse than dry.
Spacing: follow the variety. Crowding in a pot is the second most common cause of a stalled crop after light.
Feed: lettuce is a light feeder. Rich compost is enough for a cut-and-come-again crop; too much nitrogen gives soft leaves and tipburn.
Water: even moisture, not wet. Bottom-watering pots avoids damping off in seedlings.

What to expect, week by week

Germination in 7–10 days at 18 °C. The first fortnight after cotyledons is a stall — the plant is building roots, not leaves. Leaf harvest from about week five for loose-leaf types; hearted types take longer. Cut outer leaves and the plant keeps producing for weeks.

Varieties that suit a windowsill pot

Variety	Days to harvest	Sun recorded	Height
Amara	21	partial shade ok	0 ft. 10 in. - 2 ft. 0 in.
Arugula	10-15	partial shade ok	0-3 feet
Asian Delight	37	partial shade ok	3 feet
Australian Yellow Leaf	50-60	partial shade ok	6-12 inches
Batavia	47	partial shade ok	6-12 inches
Bellezia	35	partial shade ok	6-24 inches
Bibb	55-60	partial shade ok	6-12 inches
Black Seeded Simpson	40-50	partial shade ok	6-12 inches
Black Summer	45	partial shade ok	3 feet
Buttercrunch	55-65	partial shade ok	6-12 inches
Buttercrunch Bibb	65-75	partial shade ok	6-12 inches
Butterhead Boston	55-65	partial shade ok	6-12 inches
Canasta	65-75	partial shade ok	6-12 inches
Carlton	21	partial shade ok	3 feet
Cheap Frills Mix	21	partial shade ok	0 ft. 10 in. - 2 ft. 0 in.
Cimmaron Romaine	55-65	partial shade ok	6-12 inches
Clodia	29	partial shade ok	10-24 inches
Coastal Star	57	partial shade ok	6-12 inches

What does not work indoors

Fruiting crops — tomatoes, peppers, cucumbers — need several times the light a windowsill can give and are a poor use of a pot. Lettuce, herbs, rocket and microgreens are the crops that make indoor growing feel easy.

Questions

Can you grow lettuce indoors all year round?

Yes, but in winter at temperate latitudes you will need a small grow light. Lettuce needs about six hours of direct light a day; windowsills often deliver less than half that in December.

What is the best container for indoor lettuce?

Any pot at least 15 cm deep with drainage. Lettuce roots are shallow and wide, so a wide, shallow container suits it better than a tall narrow one.

Why is my indoor lettuce not growing?

Usually light. The other common causes are temperatures above 24 °C, overcrowding without thinning, and waterlogged roots from a pot with no drainage.

Does indoor lettuce need fertiliser?

Not for a short cut-and-come-again crop in fresh compost. Lettuce is a light feeder, and excess nitrogen produces soft growth and tipburn.

All 110 lettuce varieties → · Browse the catalogue