This is the hardest time of year for growing lettuce in our part of the world. Lettuce seed needs temperatures below 86F (30C) to germinate. That’s the highest soil temperature that lettuce seed is viable at. Higher than that and heat dormancy sets in. It takes 2.6 days at 86F (30C), which is longer than the 2.2 days at 77F (25C), and equals the time it takes at 68F (20C). Naturally, because these are average figures, varieties vary in their ability to germinate at high temperatures. You’ll want to choose heat tolerant varieties anyway, or they will just bolt (grow up to flower and seed) rather than form a head. Among the heat tolerant ones, the romaine Jericho and the Batavians are best able to germinate at high temperatures.
Cherokee is our new favorite among the Batavians, because of its wonderful dark red color. All Batavians have relatively thick juicy, crunchy leaves, and a heavy head. Our old favorite Pablo, is green tinged with red. (This photo and the Cherokee are of half-grown lettuces, not full-size). Pablo is available from Southern Exposure Seed Exchange
Cardinale is redder than Pablo, but less so than Cherokee. Swallowtail Garden Seeds has a selection of seven Batavian lettuces (also called summer crisp lettuces), including Cardinale and a couple I have not tried (Red Ball Jets and Jester).
Carioca is another red on green, less red than green. It was sold by Johnnys, but is now available from Restoration Seeds
Magenta is another darker red Batavian lettuce, sold by Johnnys.
Among the greener Batavians, we like Sierra from Southern Exposure who rate Sierra as taking 54 days. “Open-headed batavian crisphead with excellent resistance to bottom rot and tip-burn. Leaves are glossy green with reddish veins. Grows in open fashion at first, forming a compact head at maturity. Very tasty, crisp, and juicy. Holds well under high heat.”
Nevada is an all-green Batavian we really like. It’s available from Swallowtail Garden Seeds who note “outstanding, juicy nutty flavor – it is among the best tasting of all lettuces”
Concept is another green Batavian that has done well for us. It’s available from Johnnys, Swallowtail Garden Seeds Like several of the Batavians, at an adolescent stage the head is open, but at maturity it whorls around and closes up.
Loma from SESE is a smaller, dense, fast-growing spiky-leaved Batavian. This is one of the varieties I choose when I am a day or two late sowing, and I want fast-growing varieties to make up for my slackness. Ready in 49 days.
We also grow Muir, from Johnnys, who say “the slowest to bolt in our summer trials. . . . the light green, extra wavy leaves form dense heads at a small size and can be harvested as a mini or left to bulk up into large, heavy, full-size heads.”
Another less-typical Batavian is the spotted Mottistone, also from Johnnys. We used to grow this one, but there’s something about spotted lettuce in the summer that just didn’t appeal to people. They thought it was diseased, rather than fancy! it does have good flavor.
Anuenue, from SESE comes from the University of Hawaii. Anuenue is Hawaiian for “rainbow” (pronounced “ah-nu-ee-nu-ee”).] The seed is able to germinate at higher soil temperatures. We like this one (which is more like icebergs than the other Batavians are) as a change from our old reliables.
And now, back to how we actually get the lettuce seed to grow in summer. We use an outdoor nursery seedbed, sow the seeds at the end of the day, as temperatures drop, water with cold water, line up ice cubes on the soil covering the seeds, cover the seedbed with shade cloth, and then water daily with fresh-drawn cold water until we get germination. Sunflowers provide shade but also suck up a lot of water, so don’t get too close. Sheep sculptures are optional.