Lettuce is one of the easiest vegetables from which to save seed. Although it is better for genetic diversity to save seed from three or four plants you can get consistent and true results with just one plant. All you need to do is let one or two lettuces to ‘bolt’ – go to seed. Best results are obtained from main-crop lettuce that have been sown early in the year and with over-wintering lettuce grown in a greenhouse or cold frame.
A flowering lettuce plant can easily grow to 1.5 metres and will need some support
Lettuce flower are yellow and can have either black or white seeds They are highly self-fertile and unlikely to cross with a different variety grown nearby. Even so, I only save one lettuce variety a year to be sure I don’t get any cross-pollination.
As the flowers are fertilised they produce little balls of white fluff within which the seeds ripen.
If the weather is warm and dry the flowering and seed set can be very heavy which should mean a large harvest of seeds
Keep an eye on the ripening seed heads and when you can see the seeds inside it is time to harvest. I like to pinch off the seed heads, rub the seeds out and collect them in a shallow dish. I then gently blow off the chaff and put the dry seeds in an airtight jar in the fridge. If kept cool and dry, lettuce seed will keep for ten or more years.