Romaine lettuce

Cos lettuce is an annual and does not survive a Central European winter outdoors. There is no real overwintering; you sow anew every year (start indoors or in a cold frame from February/March, as young plants do not tolerate hard frost). You can extend a late harvest by lifting plants that are still growing, with their roots, before the first hard frost, standing them upright in a box of slightly damp sand and storing them cool but frost-free (cellar, unheated garden shed, never below 0 °C). This keeps the heads fresh for a few weeks.

You propagate cos lettuce exclusively by sowing. It is a light germinator: sow the seeds very thinly, covered with only about 0.5 cm of soil, or just press them in lightly so that enough light still reaches the seed. Lettuce seeds prefer to germinate cool, at roughly 12 to 18 °C. If it gets markedly warmer, germination noticeably declines (heat dormancy), and in great heat it largely fails. So in high summer, sow in a shady, cooler spot or wait for the evening. From mid-March you can start plants in seed trays and plant the young plants out after 4 to 6 weeks (at a soil temperature of at least 10 °C). Direct sowing in the bed works from mid-April; by sowing in succession every 2 to 3 weeks until the end of July, you ensure a continuous harvest. For your own seed, let a few strong plants go to seed: since lettuce is self-pollinating, true-to-type seed is well preserved, but only with open-pollinated varieties, not F1 hybrids. As soon as the flower heads are brown and dry, cut off the stems, let them dry further in a paper bag and rub out the seeds. Make sure the seed heads stay dry during ripening so that they do not go mouldy. Stored cool, dark and dry, lettuce seeds stay viable for about 1 to 3 years; if in doubt, do a small germination test beforehand on damp kitchen paper.