Botanical name (Genus species): Lactuca sativa
Planting: What do we need to know before planting for seed production?
Pollination method: Lettuce is self-pollinating so we don’t need to do anything to ensure that the seed produced will be true-to-type.
Isolation distance: Try to keep flowering lettuces at least 2m or far enough that you won’t mix up varieties if they fall over at maturity.
Population size: Viable seed can be saved from just one plant, however it is better practice to save from at least 5 plants of that variety.
As lettuce plants grow a significant flower stalk, then spacing them 30 to 40 cm apart will give them room to set seed. They will need the garden space for longer than if you were just going to eat the lettuce.
Selection: What are we looking for in good seed plants?
We are looking for good, robust, well grown plants. If we’re maintaining a variety we should check that the seed plants have the right colour and leaf shape for that variety and remove any that are off type. We should also remove any plants that bolt early before most of them go to seed or any that are not robust and healthy
Harvest: How and when do we harvest for seed?
Lettuce flowers are pollinated before they open. They then open lots of little yellow flowers progressively across the plant. After the flowers are open they then close again and some days later reopen to show the fluffy seed dispersal mechanism that helps the seed travel on the breeze to new locations. The seed does not all mature at once on the plant. So picking the right time to harvest is a trade-off between having the early seed fall in the garden if we wait too long and the last seed not fully mature if we harvest too early. We aim for a balance and cut the stalk when about 60% of the seed heads are ‘fluffy’. An alternative is to go out daily and individually pick fluffy seed heads. Or the seed stalks and heads can be covered with fine mesh bags to try and catch any seed falling before harvest. It is useful to remember that the seed that matures first is usually the best quality seed.
Harvested stalks can be put into bags (eg. old pillowcases) and left to dry.
Processing: How do we separate the seed from the plant material?
Lettuce seed is a small, elongated seed, ranging from light grey to dark brown.
Some seed will fall into the bottom of the bag while drying. Some varieties seem to hold on to their seed more firmly than others. Rubbing the seed heads usually dislodges the seeds reasonably easily. Seed heads can be rubbed through a sieve, or on a rubber mat, or the bags can be walked on. Stalks can also be beaten against the inside of a large rubbish bin to try and dislodge the seeds.
After the seed is removed from the heads it will need to be winnowed to remove the chaff.
Storage: What do we need to do to successfully store the seed?
After processing it is a good idea to keep the seed in a paper bag in a dry location for another few weeks to ensure that any moisture being held in the seed by the plant material has a chance to dry off.
There is a fair likelihood that insect pests will have laid their eggs in or on the seed. To stop them in their tracks one of the easiest methods of control is to freeze the seed for a few days. To do this the seed must be absolutely dry first. It then must be placed in an airtight container – like a glass jar. 48 to 72 hours in the freezer is all that is required to kill pests and their eggs.
Seed is best stored in an airtight container where it is dark, cool and dry.
Contributors: Liz Worth, Julie Davies