Lettuce is among the easiest vegetables to grow, and here in Nova Scotia we can grow it for most of the year. It likes rich soil and consistent moisture, but it's really quite adaptable and can thrive in a lot of places. I think the most important thing with growing awesome lettuce is timing your plantings just right.
I like to stagger my plantings of lettuce, so that we always have some at it's peak. Our first sowings will often be in March under cover in the greenhouse, for transplanting outside around the end of April. I begin direct sowing them in the garden around the end of April also, and then again every two weeks up until hot summer weather arrives in June. Lettuce will get bitter and bolt to seed in the heat. If you can give your plants lots of water, or provide some partial shade you can extend the lettuce season into the summer.
Late-Summer/Fall plantings do great as well. I usually sow more lettuce in late August, or as soon as the heat of summer begins to cool slightly. Any time up until the end of September is still good for baby leaves. And if you have a cold frame or another protected growing place, fall-sown lettuce will keep going up until the coldest winter weather. It's not quite as cold hardy as kale and brassicas, but we'll often be harvesting it until January.
Spacing between plants depends on if you want full sized heads or loose leaves. Big full heads need about 12" between plants, but for cut-and-come-again harvesting plants can be much closer. Sometimes I'll plant densely, and then thin out and eat the baby greens leaving the remaining heads to reach full size.
We mostly direct sow lettuce at the farm, but for gardens with an abundance of slugs transplanting might be wise to give them a head start.
- Saving Lettuce Seed -
Probably my most frequently asked question from beginner seed savers is about how lettuce produces it's seed. Well, I'm glad you asked! I find lettuce a very joyful plant to observe as it flowers and sets seed. In mid-summer the once small heads will bolt and send up one tall flower spike each. Over the course of two weeks they completely transform into 3' lettuce trees, each one crowned with hundreds of yellow flowers (like little dandelion blossoms). The flowers open up unevenly over a number of weeks, and draw a lot of beneficial insects to the garden.
Despite the number of insects present, lettuce is naturally a self pollinator and it seldom crosses between varieties. I don't really isolate mine, and only very rarely see crosses.
By the end of summer and into fall those lettuce flowers will be transforming into mature, fluffy seed heads. Simply pick them off when they're at maximum fluff levels, and the seeds inside are firm and dry. Each seed head contains 10-15 seeds, and each plant can produce hundreds of seed heads... so you can see how only a handful of plants gone to seed can produce enough seed for your whole garden.
Since lettuce plants need a fairly long season to mature seed, plan to let your earliest sown plants be the ones that go to seed. Maturing seeds are very sensitive to moisture, and a poorly-timed rain can make almost-ready seed go mouldy. Try to pick all your dry seeds before any forecasted rain. On our farm we grow them mostly under cover, in a portable hoop house that allows us to quickly throw a cover over them in August to keep the seeds dry. On a farm-scale, lettuce seed production is way easier and more efficient growing under cover… you can wait for the entire plant to completely mature and harvest them all in one go.