Seed Saving from Lettuce
Lettuce flowers are self pollinating, and very rarely cross. If you plan to save seed from more than one variety of lettuce, separate them by around 12 foot or plant a tall crop in between the rows.
Select two or three good lettuces from your row, and mark them for seed. Do not save seed from any plants that bolt early, as you want to select for lettuces that stand well. Heading lettuces may need a little help for the flowering stalk to emerge; slitting the heads partially open with a knife works well.
Once the lettuces have flowered, the seeds will ripen gradually. Harvest seed daily to get the maximum yield, shaking into a bag. Or wait until a reasonable number of seeds are ready and then cut the whole plant. Put it head first into a bucket, shaking and rubbing to remove the seeds. If you leave the whole cut plant upside down in the bucket somewhere dry, slightly immature seeds will continue to ripen over the next few days.
Most of what you have collected in the bucket will be white ‘feathers’ and chaff. To sort the seed, shake it gently in a kitchen sieve. Some seeds will fall through the sieve, with the rest collecting in the bottom. The feathers and chaff will rise to the top, and you can pick them off. There’s no need to get the seed completely clean; a little chaff stored and planted along with the seeds won’t cause any harm.
If the seed feels a little damp, dry it further on a plate before labelling and storing.
Lettuce seed should keep for around three years, provided it is kept cool and dry.