Growing lettuce under cover

Why grow lettuces under cover?

If you wish to enjoy spring lettuces, they should be sown between February and March, a particularly cold period in the garden. Their sowing must therefore necessarily take place under cover, that is to say in a greenhouse, a tunnel, or a cold frame.

Protection is also necessary for winter lettuces which are sown at the end of summer. Growing them under cover allows you to protect them from frost and the harsh weather typical of this season.

Many gardeners choose to protect their lettuces, particularly their seedlings, for another good reason: the presence of slugs and snails that feast on the young plants as soon as they emerge from the soil.

By opting for sowing under cover, you therefore protect your salads from the cold, but also from gastropods! Additionally, if they are sown in trays, your lettuces will be transplanted into the ground once they have reached a sufficient size to no longer attract slugs.

Which varieties of lettuce to grow under cover?

On the side of spring lettuces to sow under cover, we could mention:

• the ‘Gotte jaune d’or’ which produces lovely small heads of golden-green with tender leaves;
• the ‘Reine de Mai’ with delicious pale green leaves slightly tinged with red;
• the ‘Novappia’ which forms large heads of pale green with smooth, fine, and tender leaves;
• or even the very productive ‘Batavia Barcelona’ with beautiful, very dense, and crunchy heads.

On the side of winter lettuces, to grow under protection, we find for example:

• the ‘Val d’orge’ which forms large heads of pale green;
• the ‘Passion blonde’ with compact heads made up of wide green leaves speckled with reddish-brown;
• the ‘Merveille d’hiver’ whose elongated heads offer pale green leaves that are slightly blistered;
• or even the ‘Brune d’hiver’ with undulating leaves tinged with reddish-brown.

Sowing lettuce under cover

Whatever shelter you choose for sowing your lettuces, be careful that temperatures do not exceed 20°C. This is the upper limit for proper germination of this plant. Additionally, the shelter must provide enough light for your seeds to germinate.

Sowing Lettuce in a Cold Frame

The cold frame allows you to sow your lettuce seeds directly in place from the end of winter, in February-March. Make sure to position your frame in a sunny spot so that your young plants benefit from maximum warmth.

Sowing lettuce in a cold frame

• Sow thinly and in rows across the entire available surface.
• Lightly rake the soil and firm it down with the back of the rake.
• Water
• Install a winter cover and close your frame.
• Once germination begins, slightly open the cold frame to harden off the lettuces.

Sowing Lettuce in a Tunnel

The tunnel is a modular installation that is relatively easy to set up, move, and store. This setup is sometimes referred to as a “tunnel greenhouse.” Here, lettuce is sown directly in the ground.

Lettuce under tunnel greenhouse (Photos: Mark Levisay & Sara and Jason – Flickr)

• Sow thinly, ensuring rows are spaced 30 to 45 cm apart.
• Avoid burying the seeds too deeply.
• Keep the soil cool without waterlogging it.
• Germination usually occurs within 10 days (varies depending on soil temperature).

Sowing Lettuce in a Greenhouse

Under a greenhouse or a mini-greenhouse, lettuces are sown in trays or pots.

• Fill the container halfway with special sowing compost.
• Water using a spray bottle before finishing filling the space.
• Plant the seed and cover with about 0.5 cm of compost.
• Water lightly, again using the spray bottle.
• Place in the greenhouse at temperatures between 12 and 15°C and keep moist.

Thin and transplant lettuce grown under cover

Thinning Lettuce Sown Under Frames and Tunnels

Between 4 and 5 weeks after sowing, your lettuce young plants will have reached the stage of 4 to 5 leaves. It is then time to thin them out to keep one young plant every 25 to 30 cm along the row. Afterwards, water the remaining lettuces generously.

Note: instead of discarding the “removed” young plants, you can also transplant them elsewhere in the garden (see below).

Transplanting Lettuce Sown Under Glass

Again, count on a month for your seeds sown under glass to produce seedlings with 4 to 5 leaves. At this point, it is time to transplant them to the vegetable garden and under the protection of a tunnel.

Transplanting Lettuce

• Prepare the soil beforehand by breaking up the soil and adding a base fertiliser if necessary.
• Plant the lettuces at a rate of one every 25 to 30 cm along the row (also maintain a distance of 30 to 45 cm between the ranks).
• Water generously to encourage rooting.
• Protect the young plants by closing the tunnel.

What about the salad cloche?

Your lettuces can also be protected from the cold, bad weather, and predators thanks to the use of salad cloches. These allow you to recreate an environment conducive to the growth of lettuces, without taking up space in the garden.

Salad cloches

Be sure to ventilate the cloches regularly to control condensation inside. During the hot season, remove your salad cloches to avoid exposing the plant to excessively high temperatures.