The short version: Sow in the evening into a watered drill and shade the row until the seedlings are up. Keep it damp with a fine rose. Lettuce seed sits dormant in soil above about 25 degrees, so raise it in watered punnets chilled in the fridge for a day or two. Or wait for the heat to break, which is often wiser.
Should you sow at all
A few days of 35 degrees and over is unlikely to hurt a packet of seed in a cool indoor drawer, and a sowing made a week later usually catches up. Sow through it when the season is short, when you are sowing heat lovers such as beans, corn, zucchini or cucumber that like warm soil, or when you can give the row real shade, which keeps the soil at seed depth far cooler than the air.
How to sow through it
- Sow in the evening, after the sun is off the bed, so the seed gets a cool, moist night first.
- Draw the drill and water it well before sowing, so the seed goes onto wet soil; a heavy watering after sowing can shift small seed and crust the surface.
- Sow at the deep end of the range on the packet, where the soil is cooler and stays damp, except seed the packet says to barely cover, such as lettuce.
- Cover the row. Shade cloth of 30 to 50 per cent on hoops, open at the sides, suits any seed. A plank laid over the drill suits larger seed such as beans and beetroot and holds moisture in; lift it each morning and remove it the day the first shoots appear, or they stretch and bleach.
- Check morning and evening and water with a fine rose as the surface dries, keeping the soil damp down to the seed without washing it out or leaving it sodden.
- Once the seedlings are up, leave the cloth on for a week or two, then harden them to full sun by taking it off for a few more hours each day.
Lettuce and other cool-season seed
Lettuce seed goes dormant in soil above about 25 degrees, the exact point depending on the variety, and simply sits there. Chilling the dry packet does little; the seed needs to take up water while it is cool. Sow it in punnets, water them, stand them in the fridge for a day or two, then keep them in the coolest spot and plant out when the heat breaks. Spinach and coriander are also reluctant in hot soil, and they, with rocket, bolt soon after coming up.
If the week looks brutal, a packet left in the drawer loses little, and the row sown after the heat breaks is often the one that feeds you.
Related reading
Choose the heat lovers for a summer sowing from the vegetable seeds collection.