Though lettuces are cool weather plants, certain varieties have been developed specifically to tolerate summer temperatures. Summer lettuces will still need a bit of extra care, but with the right growing conditions, you can grow bolt-resistant, heat tolerant lettuces well into the summer. In fact, with some planning it's possible to grow lettuces almost year-round in most hardiness zones! Read on for tips on growing summer lettuces and the best heat tolerant varieties of every type of lettuce.
Skip Ahead: Tips for Growing Summer Lettuces • Vivian Romaine • Parris Island Cos • Salad Bowl Blend • Marvel of Four Seasons • Ice Queen • Great Lakes 118 • Black Seeded Simpson • Buttercrunch
Tips for Growing Summer Lettuces
Even heat tolerant lettuces need a bit of extra care to ensure they keep growing well into the summer months. The more you can do to limit stress on the plants, the more likely you are to have an abundant, healthy lettuce harvest. Here are a few tips to keep in mind:
- Mulch 1-2 inches: Mulching your lettuces will help to keep the soil cool and retain moisture, potentially lengthening your harvest. A couple of inches of shredded dried leaves, compost, straw, or dried grass clippings are all good options.
- Water regularly: Cool, moist soil helps keep lettuces healthy, preventing premature bolting. No amount of water will save a lettuce that wants to bolt in midsummer, but making sure the top inch of soil is kept moist will extend your harvest for heat tolerant varieties. This is especially important if you're growing lettuce in containers.
- Give afternoon shade: If you live in a very warm climate, giving lettuces some shade in the afternoon can prevent unnecessary stress on the plant. Many varieties grow well in part shade (4 hours of sun daily), so it's ideal to position the plants so that they'll get those 4 hours in the early part of the day. Alternatively, you can cover the plants with shade cloths.
- Don't overcrowd plants: Planting lettuces too closely will lead to lots of competition for water and nutrients, creating more stress that will likely cause them to bolt prematurely. Lettuce sizes vary widely, so check your seed packet for spacing instructions.
1. Vivian Romaine
Vivian is a variety of romaine (cos) lettuce that's perfect for crisp salads and wraps. It's bred for bolt resistance, so it'll keep growing tall, 12-16 inch leaves into the summer as long as it's given adequate water. Vivian is also frost tolerant, so it'll grow well all the way from the early spring into midsummer. Leaves are ready to harvest as soon as 28 days, or closer to two months after sowing, if you want to harvest the whole head at once.
Order: Vivian Romaine Lettuce Seeds
2. Parris Island Cos
Parris Island Cos was developed by Clemson University in South Carolina-- a good indicator that it'll do well in the summer heat. One of the most popular romaine varieties, Parris Island produces crisp, sweet leaves that are ideal for Caesar salads. The leaves grow 10-12 inches tall and are ready to harvest as early as 21 days after sowing, but take around 68 days to develop a mature head. This is also an heirloom variety, meaning you can let it bolt, keep the seeds, and sow them next year for an identical crop.
Order: Paris Island Cos Lettuce Seeds
3. Salad Bowl Blend (Loose leaf)
Salad Bowl Blend makes for great spring baby greens or summer salads. It's a combination of Red Salad Bowl and Green Salad Bowl varieties, both of which can grow in the summer heat without developing an overly bitter flavor. The leaves will grow 6-8 inches tall and mature after about 50 days from sowing, at which point they'll have developed colorful red tips and rosettes. For baby greens, start harvesting as early as 21 days. This is another heirloom variety, so any plants that do bolt will produce viable seeds for next year's garden.
Order: Salad Bowl Blend Lettuce Seeds
4. Marvel of Four Seasons (Butterhead)
Marvel of Four Seasons is an heirloom variety and one of the most popular lettuces for summer gardens, as it's slow to bolt and forms beautifully rich, red leaves as the temperatures climb. It has a buttery flavor that won't turn bitter in the heat, provided the plant is kept in moist soil. Though it grows too big for most containers-- up to a foot wide-- Marvel of Four Seasons is a cut-and-come-again variety, giving you multiple harvests before it needs to be pulled up in mid- to late summer.
Order: Marvel of Four Seasons Lettuce Seeds
5. Ice Queen (Crisphead)
Contrary to the name, Ice Queen is actually a heat tolerant lettuce that grows very well into the summer months if given enough water and adequate mulching. It's an heirloom iceberg lettuce (or "crisphead" lettuce) whose compact growth habit makes it great for growing in containers. These lettuces reach just 6-10 inches tall and about 8 inches wide, and unlike most crisphead varieties, they offer loose outer leaves that can be harvested before the plant has reached maturity.
Ice Queen has a relatively open growth habit for a crisphead lettuce, so you can start harvesting the outer leaves as early as 21 days after sowing. To harvest the head, wait about two months after sowing.
Order: Ice Queen Crisphead Lettuce Seeds
6. Great Lakes 118 (Crisphead)
Great Lakes 118 is an heirloom iceberg lettuce variety that produces a super compact, crisp head. It's a great lettuce for container gardens thanks to its compact size, but it's also heat tolerant, bolt resistant, and frost tolerant. These crisphead lettuces grow to maturity in 68-82 days, at which point the entire plant is harvested at once. If you do lose a plant to bolting, keep the seeds for planting next year!
Order: Great Lakes 118 Lettuce Seeds
7. Black Seeded Simpson (Loose leaf)
Black Seeded Simpson is an heirloom loose leaf lettuce variety that dates back to 1850. It produces some of the most tender leaves of any loose leaf variety, giving a slightly sweet taste. Its light green leaves will grow to about 8 inches tall, although it will need slightly more space than other loose leafs-- aim for 10-12 inches. Black Seeded Simpson is slow to bolt, frost tolerant, and fast maturing-- leaves can be ready for harvest in about 21 days. This is also a cut-and-come-again variety, giving multiple harvests in one season.
Order: Black Seeded Simpson Lettuce Seeds
8. Buttercrunch (Butterhead)
Buttercrunch is a frost tolerant butterhead (or bibb) lettuce that also performs well into the summer. In addition to being bolt-resistant, Buttercrunch has a compact growth habit that makes it ideal for container gardening. Expect very tender, buttery, light green leaves that grow just 3-5 inches tall and are a fantastic addition to a spring or summer salad. You can start harvesting baby greens from this variety after 21 days, and the plant will reach maturity about 65 days after sowing.
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