Lettuce is my favorite crop, and over the years we’ve grown hundreds of kinds. It is a beautiful crop, and well adapted to our northern climates in the summer and southern climates in the winter. Lettuce goes in the first part of our rotation, ready to benefit from all the fertility we can give it. It is best grown fast, and we don’t want anything to hold it back.
There are literally thousands of cultivars, ranging in color, shape, and leaf type from tiny, smooth-leaved bibbs to large, savoyed red romaines. I once visited a trial planting outside Yuma, AZ that had over 2,500 different kinds on display!
We classify lettuces into roughly five types.
The largest class of lettuces is the bibbs or butterheads. They have soft, tender leaves and relatively loose heads. Colors range from a rich burgundy and gold to light green flecked with pink and beautiful rich grassy greens. Within the butterhead group are some of the most heat- and cold-tolerant lettuces known, and they can be grown nearly year-round almost anywhere in the country, with the proper choice of cultivar and a little extra attention.
Crisphead lettuce has firmer, tighter heads than butterheads. Here in America we call this kind of lettuce “iceberg,” but in Europe it is known as Batavian lettuce. Crispheads do, indeed, have crispy leaves, though with less flavor than other types due to the blanching of the inner leaves. Here, too, there are cultivars in just about every color from scarlet to shamrock green.
The third type is looseleaf lettuces, which for the most part do not form heads. In general these are the earliest to mature, and are probably the most common kind in home gardens. The leaves can be smooth or savoyed, pointed, lobed, curled, or ruffled. Colors cross the rainbow from deep Merlot red to pale greenish yellow, with just about every combination in between.
Romaine, or cos lettuces are tall, upright, with thick-leaves; their thick midribs and juicy texture have made them especially prized for certain salads. They range in size and color from tiny eight-inch-tall mini-romaines to large, smooth-leaved heads that can reach almost two feet in height.
Our last type is really a catch-all category for those lettuces that don’t seem to fit into any one group, but share something from a couple: almost-butterheads that are just a bit too tall and whose leaves are more substantial; looseleaf lettuces that, if left to mature, will form a small head surrounded by their normal complement of widely splayed foliage; or the reverse—crispheads that can be cut when young like a looseleaf.
We grow almost all our lettuce from transplant. The first batch of seedlings is sown eight to ten weeks before the frost-free date to be ready for transplanting as soon as the beds can be prepared. From that point on we start enough plants every week to provide for a week of harvest time. Depending on the size at which you harvest, that might be anywhere from six to twelve plants per four person family per week.
When the bed is ready we set the plants out on twelve-inch centers, which is a 3:2:3 pattern on our three-foot beds. If you like really big heads (and are using a cultivar like Red Sails that is capable of producing them), you can set them on eighteen-inch centers, which is a 2:1:2 pattern. If the weather is particularly cold during a given spring, we might cover the first planting with a floating row cover, but other than that they will require no more attention (beyond regular, shallow cultivation) until harvest. This cycle of seeding, transplant, cultivation, and harvest is kept up right through the growing season, with a change of cultivar as the weather, season, and our own needs dictate. During the hottest part of the summer we make sure to shade the beds after transplanting and water more frequently to keep the lettuce from succumbing to heat stress, which especially combined wit the long days of early summer, leads to bolting and bitterness.
If you prefer to direct-seed lettuce you can begin as soon as the soil can be worked in spring. You’ll probably have an easier time managing the planting if you sow the seed in short rows across the bed. That way you can simply plant a row or two a week. The process, however, is essentially the same, except that you’ll have to thin the rows—actually a bonus, since the thinnings are some of the best salads there are. The seed should be set only 1/4 to 1/2 inches deep, in rows six to twelve inches apart (depending on how large you want the plants to get), and thinned as soon as it reaches a few inches high, first to a couple of inches between plants, and later to the full distance you’d have with transplants.
Thinning isn’t actually necessary unless you want to harvest mature heads: you can simply keep sowing and harvesting young plants. Some gardeners sow the seed as thinly as possible, let the plants grow up to, say, four to six inches tall, cut all they want with scissors—direct into the salad bowl—and then either replant or let the plants regrow for another harvest. For the ultimate in this kind of culture, mix the seed of a range of salad plants—lettuce is best, but you don’t need to limit yourself to it—then broadcast the seed on a section of the bed, rake it in, and water. Three weeks later you’ll have a ready-made mixed salad just for the trouble of cutting!
When the weather turns hot you’ll have to trick the lettuce into germinating, because it has a built-in dormancy trigger that won’t allow it to sprout if the soil temperature is above 80˚ F (27˚ C). Your best results will come from sowing in the early morning, when the soil is coolest, watering thoroughly and then covering the rows with pieces of 2×6-inch piece of lumber to insulate them from the heat of the sun. Broadcast sowings can be shaded with a piece of plywood supported above the bed on cinder blocks or pieces of firewood. Either way, be sure to check underneath daily because once lettuce sprouts it needs light immediately.
If you want to try overwintering lettuce in a cold frame or simply out in the garden with a floating row cover for protection, start the seedlings a month before the first fall frost, or in late September, whichever is earlier. Particularly in the North, where day lengths shorten rapidly in late summer, the lettuces need time to grow to a size where they can withstand lower winter temperatures and regrow in spring. The ideal size is about four inches in diameter with only a half-dozen leaves or so.
Don’t cover them until the ground is frozen; otherwise you won’t be able to keep the bed cultivated to kill late-growing, cold-tolerant weeds like chickweed.
There are so many good lettuces it is hard to recommend just a few, but if I had to choose I would probably grow one or two from each group. Space-conscious gardeners should consider buying a mixed packet; many different mixes are now available.