The Best 7 Lettuce Types to Grow During Summer Months

The optimal growing conditions for lettuce, a plant frequently found in cooler seasons, are when temperatures are lower than 68°F/20°C, typically in the fall or spring. It’s worth mentioning that this biennial plant could potentially bolt if subjected to hotter temperatures.

Of all the vegetables consumed, lettuce has the highest per capita consumption rate in the United States, a staggering 23.4 pounds in 2021. Leaf lettuce is the most popular (54%). The thermal dormancy of lettuce will prevent it from germinating if the soil is too warm or cold.  

Growing Summer Lettuce

Lettuce is a high-value crop, and in a world where annual temperatures are ever-increasing, developing heat-tolerant lettuce is a growing priority. Unsurprisingly, the University of California is the leader in summer lettuce research. 

Lettuce is California’s fifth-largest commodity, with a market value of over US$3 billion. Lettuce is a widely grown crop worldwide, with different regions favoring different varieties. 

The average annual lettuce consumption in the United States has dropped since prices have rocketed to $3.58 per pound (Average Romaine lettuce price in Dec 2022). The United States exports 3.6 million tons of lettuce annually. 

"Photo of several rows of green lettuces growing in a garden under the bright sunlight. The leaves are lush and vibrant, with shades of deep green and lighter green. Some plants have droplets of water on their leaves, suggesting recent watering. The background shows a natural outdoor setting."
“Freshly grown and thriving – a garden bed full of vibrant green lettuces soaking up the sun.”

China grows more lettuce than any other country, about 13.5 million tons annually, mainly for local consumption, and Spain exports just under a million tons annually.

Used as a garnish in most fast food products, lettuce is in demand, and finding solutions for growing lettuce without the risk of early bolting is essential.

In 2015/16, Sacromento’s Fair Oaks Horticulture Center did some trials on lettuce bolting times and temperatures. More recently, the University of Delaware and the Practical Farmers of Iowa (PFI) did similar tests.

We want to beat the heat and find the most heat-resistant or heat-tolerant lettuce plants. My efforts are informal, and I hope you also push the boundaries, establishing what works in your area.

The Fundamental Temperature Needs of Lettuce Plants

Lettuce is a cool-season vegetable, and seeds will germinate at 35°F/1.6°C, but the optimum soil temperature is 70 to 75°F/21 – 24°C. The maximum temperature at which lettuce seeds will germinate is 85°F/29.4°C. 

Extended periods of temperatures above 85°F/29.4°C will cause lettuce to bolt, a common challenge to growing lettuce in summer. If growing lettuce in summer, ensure afternoon shade, as too much sun is a bolting factor.

Lettuce seed needs light to germinate, but plants do well with three to five hours of sunlight, avoiding the midday sun. Taller plants can be grown as companions to cast some shade, though this is less likely during the middle of the day when the lettuce plants need it most.

Plant Bolting

Several garden vegetables a biennial plans grown as annuals. Biennial plants grow roots and strengthen their foliage in year one to produce potent, resilient, healthy seeds in year two.

The plants rush the seed production process when the environment changes (more light and higher temperatures). Gardeners call it bolting, and it generally refers to vegetable plants that begin flowering.

Unfortunately, bolting can diminish the quality of your harvest. Lettuce plants develop a bitter taste as they devote more resources to flowering and seed production.

Close-up of a green lettuce leaf with curly edges, showing the texture and veins of the leaf.
“Up close and personal with this vibrant lettuce leaf 🌿👀 #FreshAndCrisp.”

If you want to grow lettuce in summer, look for “slow bolting” seeds. Grow loose-leaf varieties that allow you to harvest outer leaves while the plant is still young.

Remove spent plants to avoid volunteer lettuce plants. Replace spent plants with fresh lettuce plants to keep your summer garden vibrant.

Sowing Lettuce Seeds

Several bloggers suggest direct seeding; while possible, the risks outweigh any benefits. Lettuce plant seeds are disease prone, and I advise gardeners not to produce seeds from previous crops.

Instead, purchase your seeds from a reputable producer that certifies their stock. 

How to Grow Lettuce in Summer

Summer Site Selection

Please remember that growing lettuce in summer is reserved for cooler climates or controlled environments. There are several summer crops, but lettuce is not one of them. Avoid growing lettuce in summer in hot climates.

That said, cooler climates allow year-round lettuce production, and I imagine it won’t be long before Washington State and other northern states become significant producers. Washington State is already the second biggest vegetable crop producer (after California).

A photo of a hydroponic system with rows of green lettuce plants growing in small containers filled with nutrient-rich water. The plants are arranged neatly in straight lines and illuminated by artificial lights above them. The background is dark and blurry, emphasizing the bright green color of the lettuce leaves.
“Thriving hydroponic lettuce farm under artificial lights, showcasing sustainable farming for a greener future.”

Lettuce may bolt in reaction to high-temperature stress, and the leaves may become bitter when the plant transitions to flowering (see photo at right). If the plant becomes water stressed in hot weather, the leaves wilt, toughen, and become bitter.

Managing Summer Temperatures

To successfully grow lettuce in warm weather, consider the following strategies:

  • Germinate seeds indoors, managing light, soil moisture, and soil temperatures well.
  • Use shade cloth or grow taller plants as companion plantings to cast shade on your lettuce plants, especially in the midday sun. Taller vegetables include sweet corn, stalk beans, and other vining crops.
  • Water must absorb heat from the surrounding environment to evaporate, causing it to cool. Water adequately in hot weather, keeping the soil moist but not wet. Lettuce plants need damp soil.
  • Mulch lightly with organic mulch to retain moisture and insulate the soil from the sun, keeping temperatures constantly lower.
  • Harvest outer leaves with sterile tools to promote fresh regrowth.
  • Plant lettuce seeds and transplants in succession to reduce the number of aged plants in a crop.
  • Keep nutrition levels up to boost foliar growth. Happy plants don become bitter and bolt, and happy plants have some shade, enough water, and nutrition.
  • Examine the plants for insects and illnesses. Destructive insects must be hand-picked and destroyed. Rouge any unhealthy leaves or plants.
  • A light layer of organic mulch works wonders. 

Using Shade Cloth

Rows of lettuce plants are visible in the foreground, thriving underneath a green shade cloth that covers the entire area. The lettuce leaves are a vibrant shade of green and appear healthy and well-nourished. The soil in which the plants are growing is neatly groomed and free of any debris or weeds.
“Thriving lettuce under shade cloth, with healthy rows and vibrant leaves.”

Please do not cool your growing lettuce by wetting leaves. Summer stress vectors abound, and wet leaves will cause rapid pathogen spreads and diseases. Keep the soil moist and relaxed, the leaves dry, and the lettuce under a shade cloth in the midday sun.

Lettuce: 7 Heat Tolerant Lettuce Varieties

All lettuce bolts and those that don’t may become bitter if exposed to high temperatures and long days of bright light. Heat tolerance is relative, but some varieties are slower to bolt in the summer heat.

Leaf lettuce allows early harvesting, and romaine lettuce has a reputation for being more heat resilient. My table below lists 21 varieties, of which 10 are leaf lettuces and no Iceberg lettuce. 

That’s because loose-leaf lettuces have better airflow and heat dissipation mechanisms than head lettuces. That’s a generalization because Romaine lettuce forms heads but is much less compact than iceberg, and loose-leaf lettuce is one of the best warm-season varieties.

Below is a table of 21 heat-tolerant lettuce varieties, with my selection of the top seven listed first and in order of preference. Several heat-tolerant options are hybrids developed by Johnny’s Select Seeds.

#VarietyTypeDays to MaturityComment
1MuirBatavian50Extremely heat tolerant
2SkyphosButterhead Lettuce 47Heat-tolerant
3Salanova® Green ButterButterhead Lettuce 55Excellent bolt tolerance.
4Salanova® Red ButterButterhead Lettuce56Excellent bolt tolerance.
5SunlandRomaine Lettuce56Great summer performance
6SparxRomaine Lettuce58Ideal for summer harvests.
7CaseyButterhead Lettuce55Heat tolerant in controlled environments
8CimmaronRomaine Lettuce35Excellent bolt resistance
9Black-Seeded SimpsonLeaf Lettuces45Drought and heat tolerant
10Grand RapidsLeaf Lettuces45Heat tolerant 
11Green StarLeaf Lettuces 45Heat tolerant
12SloboltLeaf Lettuces45Good warm-weather lettuce
13Bronze OakleafLeaf50Good resistance to hot spells
14Red Salad BowlLeaf55Good heat tolerance.
15Salad BowlLeaf55Good resistance to bolting.
16RubyLeaf55Good bolt and heat resistance
17White BostonBoston Lettuce57Performs well in warm, humid conditions
18ButtercrunchButterhead Lettuce68Heat tolerant
19IthacaCrisphead Lettuce72Does well in summer.
20Summer BibbBibb Lettuce77Slow to bolt
21Great LakesLeaf Lettuce85Slow to bolt

1. Muir

A close-up photo of Muir Lettuce leaves, showing their vibrant green color and delicate texture. Muir Lettuce is a sweet and flavorful variety of lettuce.
“Enjoying the vibrant color and delicate texture of Muir Lettuce, a sweet and flavorful variety.”

Muir Lettuce is a variety that is slightly sweeter and more flavorful than other types of lettuce. It is a hardy variety of lettuce capable of growing in many climates. 

It has large, juicy leaves with a light green color and a hint of bronze. The leaves are also very crisp and have a mild, slightly sweet flavor. Muir lettuce is ideal for salads, sandwiches, wraps, and other recipes. 

It is also a great dietary fiber, vitamin, and mineral source.

Muir lettuce is exceptionally tolerant of hot days, and trials have repeatedly been the slowest to bolt. Only buy seeds with certified resistance to downy mildew and bushy tomato stunt virus (lettuce dieback complex).

2. Skyphos

A close-up photograph of a green leafy vegetable, known as Skyphos lettuce. The lettuce has a crinkled texture and the leaves are slightly curled, giving it a fluffy appearance. The light shines on the lettuce from the top, highlighting its fresh and vibrant color.
“Fresh and Fluffy Skyphos Lettuce – A vibrant green leafy vegetable with a crinkled texture and slightly curled leaves, illuminated by a shining light from above.”

Skyphos lettuce is a loose-leaf lettuce with a unique, crinkled texture and a sweet and mild flavor. It is famous for salad greens, sandwiches, wraps, and garnishing plates. 

Skyphos lettuce is relatively easy to grow and can be harvested in as little as four weeks. The plant is deep green, and the leaves are thick and tender. 

It is also very resistant to bolting and can grow in various temperatures, making it an excellent choice for multiple climates.

3. Salanova® Green Butter

"Close-up photo of a head of green Butter lettuce, showcasing its large, loose leaves with ruffled edges. The leaves are vibrant green and slightly curly, with a smooth surface and a soft texture. The lettuce is displayed on a white background, emphasizing its natural beauty. This variety of lettuce is known for its mild, buttery flavor and is a popular choice for salads and sandwiches."
“Fresh and vibrant Butter lettuce, perfect for flavoring your favorite salads and sandwiches. 🌿🥗 #ButterLettuce #FreshFlavors”

Salanova® Green Butter lettuce was developed by the Dutch company Bejo Seeds in 2005. Salanova® Green Butter lettuce is a large, loose-leaf with a mild, buttery flavor, and it is an excellent choice for salads, sandwiches, and wraps. 

The leaves are divided into sections, giving the lettuce its distinctive look. Salanova® Green Butter lettuce is also known for its high content of vitamins A and C and other essential vitamins and minerals. This lettuce variety is easy to grow and maintain in the home garden and is resistant to bolting.

4. Salanova® Red Butter

"Close-up of Salanova® Red Butter lettuce leaves showcasing their dark red color, loose head shape, and delicate texture. The lettuce variety was developed by Dutch seed company Rijk Zwaan and is known for its sweet flavor."
“Experience the rich color and sweet flavor of Salanova® Red Butter lettuce – a perfect addition to any salad!”

Salanova® Red Butter lettuce is a variety of lettuce developed by the Dutch seed company Rijk Zwaan and has a dark red color, a sweet flavor, and a loose head shape. 

The leaves are slightly crunchy and have a mild, buttery taste. Salanova® Red Butter lettuce is famous for salads, sandwiches, wraps, and other dishes, and it is also a great source of vitamins and minerals.

5. Sunland

A photo of a head of Sunland lettuce, a type of romaine lettuce grown in the San Joaquin Valley of California. The lettuce is vibrant green with long, crisp leaves that curl slightly at the edges. The head of lettuce is surrounded by other lettuce plants in the background.
“Fresh from California’s San Joaquin Valley fields, behold the vibrant green goodness of Sunland lettuce!”

Sunland lettuce is romaine grown in the San Joaquin Valley of California. It is a high-quality variety well-suited for salads, sandwiches, and wraps. Sunland lettuce is produced in a unique environment that combines the ideal soil, climate, and irrigation. 

This combination produces a unique flavor and texture unmatched by other lettuces. Sunland lettuce is also known for its high nutritional value, packed with essential vitamins, minerals, and antioxidants. 

Its high nutritional content is why it is a popular choice for health-conscious consumers.

6. Sparx

"Fresh green Sparx lettuce leaves arranged on top of a rustic brown wooden table. The table's natural wood grain and texture add warmth and contrast to the vibrant green lettuce leaves, creating an appealing visual composition. Sparx lettuce is a nutrient-rich and flavorful variety of lettuce that is a great addition to any healthy meal."
“Fresh, vibrant, and nutritious. Sparx lettuce on a rustic table.”

Sparx lettuce is a unique variety known for its high levels of nutrition and flavor. It is a chicory family member and is a cross between iceberg and romaine lettuce. 

It has a bright, crisp texture and a sweet, nutty flavor. It is rich in vitamins A, C, and K, folate, iron, and calcium. It is also a good source of dietary fiber. Sparx lettuce is a popular choice for salads, sandwiches, and wraps.

7. Casey

A photo of a green lettuce leaf with frilly edges, sitting on a white background. The lettuce is a Casey Lettuce, a hybrid variety of lettuce that was developed in Australia.
“Fresh and Frilly: Meet Casey Lettuce, the Aussie hybrid with a unique crunch!”

Casey Lettuce is a hybrid variety of lettuce developed in Australia. It has a medium-green leaf with a firm, crunchy texture and a sweet, mild flavor. 

Casey Lettuce is one of Australia’s most popular varieties and is also grown in New Zealand, the United States, and several other countries. 

It is commonly used as a salad green but can also be eaten cooked or a topping for sandwiches. Casey Lettuce is a cool-season crop, best planted in the early spring or late summer.

FAQs on The Best 7 Lettuce Types to Grow During Summer Months

Can you grow lettuce all summer?
Lettuce is a cool-season crop, but growing it in summer in cooler climates or controlled environments is possible. Planting slow-bolting lettuce varieties and providing afternoon shade can help prevent bolting.

What lettuce is easiest to grow?
Loose-leaf lettuce is considered the easiest to grow because it requires less maintenance than other varieties, and you can harvest the leaves while the plant is still young. Also, loose-leaf lettuce tends to be more resistant to bolting, a common challenge to growing lettuce in summer.

Which lettuce lasts the longest?
Romaine lettuce generally lasts the longest among lettuce varieties. This lettuce type can stay fresh for up to two weeks when stored correctly in the refrigerator. However, it’s essential to note that the longevity of lettuce also depends on its freshness at the time of purchase, proper storage, and the temperature and humidity of the environment.

In Closing

If you plant lettuce in early spring, you can beat the heat and get a crop mid-summer. If your local climate is warm, you must use every resource to keep the lettuce plants cool enough not to bolt.

Shade cloth, mulching, persistently moist soil, and a close eye for pests are some tasks that are less important in cooler weather. 

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