🌱✗ Tested and false“Lettuce bolts because of hot weather — nothing you can do”
Heat is one trigger but not the only one, and bolt-resistant varieties exist. Dryness at the roots, overcrowding and variety choice are all factors under your control. Choosing a bolt-resistant variety and keeping the soil evenly moist makes a measurable difference even in a warm spell.
What to do: Choose bolt-resistant varieties and keep the soil moist rather than letting it dry between waterings. Sow successionally so a bolted row is replaced rather than mourned.
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- RHSDryness at the roots and overcrowding contribute to bolting; bolt-resistant varieties available
“You can grow lettuce all year round if you have a greenhouse or polytunnel”
With the right varieties and a cold frame or unheated greenhouse, you can crop lettuce in every month except midwinter, but December and January are a stretch even under cover in Scotland. Light levels, not just temperature, stop growth in the darkest weeks.
What to do: Sow winter varieties in September for cutting from October to December, and start early sowings under cover in February. Accept that the Christmas-to-mid-February gap is hard to close in Scotland without supplementary lighting.
In Scotland: The day-length problem is worse here than further south. Even an unheated polytunnel cannot add light, and December and January growth is negligible this far north.
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- RHSWinter varieties can be grown under cover; light levels affect growth in midwinter
“Cut a whole lettuce head at the base and it will regrow like cut-and-come-again”
This only works on loose-leaf varieties, not hearting types. A cos or butterhead lettuce harvested as a whole head will not regrow from the stump in any useful way. The distinction is between harvesting loose-leaf by picking outer leaves and harvesting hearted types as a whole plant.
What to do: If you want repeated cuts, grow a loose-leaf or cut-and-come-again variety and pick individual leaves. Hearting lettuce is a one-cut crop and should be replaced with a fresh sowing.
In Scotland: Cut-and-come-again varieties suit Scottish summers where a single sowing can give several cuts before bolting, and the effort-to-reward ratio is hard to beat.
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- RHSLoose-leaf types harvested by taking outer leaves; hearted types harvested as a whole plant
“Lettuce needs a full sun spot to grow well, like most vegetables”
The right spot depends on the season: full sun is fine for spring and autumn crops, but for lettuce sown or planted in high summer, light shade during the hottest part of the day is actively preferable, because heat is a direct trigger for bolting.
What to do: Give spring and autumn lettuce full sun. For summer sowings, choose a spot with some afternoon shade — under taller crops or against a north-facing fence works well.
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- RHS — How to grow LettuceA sunny spot is usually best, but if sowing/planting in the middle of summer, some light shade is preferable during the hottest part of the day, as too much heat can cause lettuces to flower prematurely.
“Pick lettuce leaves from the outside and the plant keeps producing”
This works but only on the right type. Loose-leaf and cut-and-come-again varieties genuinely produce over a period of weeks when outer leaves are harvested. The advice is to pick a few leaves from each plant rather than cut the whole head. Heading lettuces do not regrow once cut.
What to do: Grow loose-leaf varieties if you want continuous picking. Take outer leaves and leave the growing centre intact. For heading types, sow successionally instead.
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- RHSHarvest loose-leaf types by picking outer leaves; cut-and-come-again varieties crop over several weeks
“Lettuce seed won't germinate once it gets hot”
Lettuce seed genuinely enters thermal dormancy above about 25°C and germination falls sharply. Most lettuce seed will not germinate at temperatures above 25°C. The workaround is well established: sow in the evening, water with cold water, and cover with a board or fleece to keep the soil cool.
What to do: In warm spells sow in the cool of the evening and shade the row. Sow into modules somewhere cooler and transplant once the seedlings are up.
In Scotland: This is a problem we dodge more often than we face it. Soil temperatures above 25°C are a rare event in most of Scotland, and a failed summer sowing here is more likely to be slugs than heat.
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- RHSMost lettuce seed will not germinate at temperatures above 25°C
