Lettuce is self-pollinating, so it is an excellent choice for beginner seed savers and those with urban gardens with neighbouring vegetable growers. The flowers are pollinated before they open, so there is little chance of varieties getting crossed. It is usually enough to keep flowering varieties separated by just a few metres.
Sometimes things go a little awry: perhaps an insect damages the flower bud and transfers pollen into it early; or maybe flowers of two different varieties rub directly against each other and manage to transfer the pollen that way. Some sources suggest that it would not be surprising if up to five per cent of lettuce seed is actually cross-pollinated. If the other parent is the same variety we’d never notice. Carol Deppe, author of Breed Your Own Vegetable Varieties: the Gardener’s and Farmer’s Guide to Plant Breeding and Seed Saving (Chelsea Green Publishing 2000, second edition), says that she gets many more unexpected crosses than commercial seed producers. Her take on this is that her organic garden has a much higher number of pollinator insects than are found in the monoculture fields of large producers.