If you have a garden full of lettuce, mesclun, and arugula, saving your own seeds is an economical way to propagate next year's crop. Saving seeds allows you to cherry pick the varieties that perform well in your garden or heirloom varieties that are hard to obtain. Over time, seeds saved from your garden adapt to their particular growing conditions making your seeds specifically suitable to your garden, assuring a fruitful harvest.
Before you go to the effort of saving your lettuce seeds, first, make sure to save seeds only from open-pollinated or heirloom varieties. Open-pollinated and heirloom plants both grow true to seed for years to come. Open-pollinated varieties are more genetically diverse, allowing them to better adapt to specific growing conditions. Heirloom seeds represent original varieties passed down from generation to generation, assuring their vitality. Some heirloom seeds are even documented and can come from a variety that's well over 50 years old.
Hybrid seeds, on the other hand, will not grow into the same plant due next year to a phenomenon called "hybrid vigor" where certain characteristics outcompete others in subsequent crops. Saving and then planting hybrid seeds is a crap shoot. You can do it, but there's no telling what you may end up with.
Timing the Harvest
Small, tender lettuce leaves are pretty to look at and delicious to eat, but when the plant goes to seed, it looks gangly and unattractive as it bolts (sends up a flower stalk to produce seeds). The blooms resemble small dandelions and the plant gets quite tall as if it's reaching for the sun. After a bolt, it's time to harvest your seeds.
Waiting out this awkward growing cycle—when some veggies plants look plump and beautiful while the greens are past their prime—is hard to do for those who value garden aesthetics. The good news is that you don't need a lot of plants to produce seeds. In fact, one plant per variety will provide more than enough seed for next year's harvest. That said, camouflaging one or two bolting plants in your garden is easy to do. And you won't even see them if you plan your garden's layout with this in mind.
Most lettuces start to bolt when summer temperatures get hot. Once the plant sends up its seed stalk, the leaves become bitter and tough, making them unpleasant to eat. This marks the time when the plant is ready to bloom. The plant will produce small clusters of flowers. These flowers contain the plant's pollen and will eventually produce a puffball full of seeds that, if left to its own device, will disperse to other parts of the garden. Seeds take anywhere from 12 to 24 days after blooming to ripen.
If you are growing more than one variety of lettuce and they are blooming at the same time, you run the risk of cross-pollinating species. To prevent this, isolate each plant with a plastic bag or floating row cover to create a mini greenhouse over each particular species. You can also construct a cage covered in a screen and place it over an entire plant to isolate it from others. This assures the pollen of one flower won't be passed onto another variety to create a hybrid seed. If plants are situated more than 25 feet apart, you don't need to worry about crossing.
Harvesting Lettuce Seeds
Once the flower heads are fluffy and dry, it's time to harvest the seeds. There are a couple of ways to complete this process properly. One involves holding a paper bag near the plant and shaking the flower head over it daily until most of the ripened seed is gone. Alternatively, you can wait until most of the seed heads look ready to harvest, remove the entire flower stalk, and shake it over a bucket or bag to dislodge any fully-ripened seed. Both tactics will work, yet the first method takes more time and effort and the second method yields fewer seeds, since you pull the plant before they all ripen.
After seed harvest, go through your collection and remove the fluff and chaff to isolate the seeds. To do this, pour your seed onto a shallow dish or tray and gently run a fan nearby. The breeze from the fan will blow away trimmings. You can scale this process down by placing the seeds and chaff in a bowl or saucer and blowing gently. Once you remove the chaff, place your seeds in a plastic food storage bag or Mason jar, seal it, label it, and store it in a cool, dry place.