Grow Tasty Lettuce Even in the Heat of Summer – 6 Heat-Tolerant Varieties and Expert Tricks Will Keep Harvests Coming All Summer
Summer heat waves don't mean then end of the lettuce-growing season when you plant these picks. Say goodbye to bitter summer lettuce!
Plenty of lettuce quits the moment summer heat settles in, bolting tall and turning bitter before the salad season really gets going. But a few varieties were bred to hold their nerve, and those keep cutting well past the bolt.
Come July, the lettuce patch tends to be the first corner of the garden to fall apart. Leaves that were sweet and crisp back in May go bitter, the plants shoot up tall, and a flower stalk pushes from the center. Heat is the trigger. That whole stretching-and-flowering routine is bolting, and once it starts there's no going back.
Not every lettuce bolts that fast, though. The different lettuce types vary a lot in how much warmth they'll take before they turn, and a handful were bred specifically for it. Pick one of those, hand it afternoon shade and steady water, and you can keep cutting salads while the spring crop bolts and dies back.
When Heat Turns Lettuce Bitter
Lettuce is wired for cool weather. Once daytime temperatures stay in the 80s (around 27-32C), the plant takes it as a cue to reproduce, so it throws up a thick central stalk headed for flower. That's the bolt. Long summer days nudge it along too, which is why the closer you get to midsummer, the faster a susceptible variety goes.
As the plant stresses, the sap in the leaves goes milky and the flavor slides from crisp to flat-out bitter — sometimes before any stalk even shows. Germination drops off in the warmth as well, with seed often failing to sprout once the soil creeps past about 80F (27C), so a midsummer sowing may not come up at all. None of which is the end of it. It mostly comes down to which variety goes in the ground, plus a break from the afternoon sun.
6 Lettuce Varieties That Take the Heat
These are the ones that keep producing when the thermometer climbs. Most are loose-leaf or Batavian lettuce types, which run to seed slower than tight heading lettuce, and all turn up through the usual sellers.
1. Jericho
Bred in the Israeli desert, Jericho lettuce (Lactuca sativa var. longifolia) was made for exactly this problem. A tall green romaine, it stays sweet and crisp at temperatures that turn most romaines sour, and it's slow to send up a stalk even with the heat on.
Keep the moisture steady and it forms big upright heads. Take the whole thing or pull leaves a few at a time. Super Jericho seeds from the Home Depot make it easy to get.
2. Nevada
For raw durability, not much beats Nevada. A Batavian type — summer crisp on some labels — it's still Lactuca sativa var. capitata, with thick glossy leaves gathered into a loose head. It holds up to both heat and a sudden cold snap, and stays mild long after softer types would have soured. It regrows after a cut, too, so one planting goes a long way. You can find Nevada lettuce seeds at Walmart.
3. Buttercrunch
Most butterheads collapse in the heat. Buttercrunch is the exception that's kept it on seed racks for decades — a butterhead itself, Lactuca sativa var. capitata. An All-America Selections winner, it keeps that tender, buttery rosette later into warm weather than its relatives and resists bolting longer than most. It wants steady water and a bit of afternoon shade once things warm up. You'll find it nearly everywhere, including plenty of buttercrunch seed from Park Seed.
4. Black-Seeded Simpson
Black-Seeded Simpson (Lactuca sativa var. crispa) ranks among the fastest, most forgiving lettuces you can sow. The light, frilly leaves are ready in roughly 45 days, which lets you slip a harvest in ahead of peak heat and keep resowing through the season. It isn't the most bolt-proof name here, but the speed covers for that. You're eating it before it gets the chance to turn. Burpee has black-seeded Simpson seeds for a good price.
5. Red Sails
Color is what sets Red Sails apart, though the staying power is the bigger draw. The bronze-red ruffled leaves — another looseleaf, Lactuca sativa var. crispa — are slow to bolt and slow to sour, and that red pigment seems to screen it from strong sun. It's an All-America Selections pick too, a cut-and-come-again grower. Strip the outer leaves and it keeps producing for weeks instead of finishing at once. You can grab a packet of Red Sails seeds off Amazon.
6. Slobolt
The name does the explaining. Slobolt (Lactuca sativa var. crispa) was bred to resist bolting, and it holds for weeks after other loose-leaf types have shot up and gone bitter. The leaves come light green and soft, mild enough to eat young and cut again as they regrow. It sometimes turns up on store shelves less often than the others, so finding Slobolt lettuce seeds rom the Thresh Seed Co. store on Amazon is more reliable.
Expert Tips
Lettuce will hang on longer in summer if you take a little pressure off it.
- A bit of afternoon shade makes a big difference, especially once temperatures stay high.
- Keep the soil from drying out completely—lettuce hates that stop-and-start stress—and throw down some mulch if you’ve got it.
- Cut their leaves early in the morning while they’re still cool. They taste better, and the plant doesn’t seem to mind the harvest much.
