Lettuce is a cool-weather crop that can be difficult to grow in the heat of summer. However, with some careful planning and proper care, it is possible to continue harvesting lettuce even during hot summer months. This guide will provide tips and techniques for keeping lettuce growing successfully when temperatures climb.
Choose Heat-Tolerant Lettuce Varieties
Not all lettuces are created equal when it comes to heat tolerance. Seek out varieties specifically bred to withstand warmer temperatures:
Oakleaf – These looseleaf types have deeply lobed leaves that retain moisture and thickness in heat. Green oakleaf and red oakleaf offer color options.
Romaine – Look for heat-tolerant romaine varieties like Green Towers, Cimmaron, and Jericho which can form heads even in hot weather.
Latin – Latin lettuce includes hot weather performers like Tango and Sizzler. These looseleaf types have ruffled leaves.
Kagraner Sommer – This miniature Batavian type has compact 8″ heads that hold up to bolting longer than many other lettuces.
Butterhead – Summer bibb lettuces like Tom Thumb and Everett are more heat-hardy than regular butterhead.
Focus on Quick-Maturing Varieties
Fast-growing lettuces that mature quickly are less likely to bolt prematurely in heat. Prioritize quick developering lettuces:
- Looseleaf types like Black Seeded Simpson and Red Sails mature in as little as 45 days.
- Mini romaines and butterheads reach maturity several weeks before full-size varieties.
- Use a seed tape to ensure proper spacing and quick growth.
- Baby lettuce mixes offer blends of fast-growing greens.
Plant in the Right Season
Timing is everything when it comes to avoiding summer heat. Follow these tips:
- In warm climates, opt for fall, winter and early spring plantings. Take advantage of cooler temperatures.
- In northern areas, start lettuce 6-8 weeks before last expected frost for harvest before peak summer heat hits.
- Sow new seeds every 2-3 weeks for a continuous supply as each planting matures.
- Interplant quick-maturing radishes and greens to fill gaps left by bolting lettuce.
Provide Sun Protection
Give lettuce respite from the hot sun to prevent bolting and bitterness:
- Plant under the dappled shade provided by taller crops like tomatoes, trellised beans or sweet corn.
- Erect shade cloth structures to filter out 30-50% of sunlight. Use UV-stabilized fabric.
- Allow slightly more space between plants to prevent excess heat buildup.
- Mulch beds with straw to keep soil cooler and promote moisture retention.
- Use floating row covers to protect young plants, removing during the day if very hot.
Ensure Adequate Moisture
Consistent moisture is key to keeping lettuce growing in hot, dry conditions:
- Water beds thoroughly in the morning if no rain is forecast. Avoid overhead watering.
- Use drip irrigation or soaker hoses to target soil moisture while leaving leaves dry.
- Side dress with compost or add organic matter like peat to improve moisture retention.
- Use fabric row covers to trap humidity and create a greenhouse effect while plants are small.
- Add 2-3″ of organic mulch like wood chips or shredded leaves to prevent moisture loss.
- Prioritize lettuces with deeply lobed leaves that retain more water content.
Time for Milder Temperatures
When summer heat is at its peak, focus planting efforts on more heat-loving crops. Wait for natural weather shifts to replant lettuce:
- In mid to late summer, sow lettuce for fall harvest as temperatures gradually cool.
- Choose quick-maturing varieties 6-8 weeks before your first fall frost date.
- In mild winter areas, plant overwintering lettuce in late fall through early winter.
- Protect fall and winter plantings with cloches, cold frames or low tunnels when needed.
- Start lettuce indoors 2-4 weeks before last spring frost for an early start to the season.
Prevent Early Bolting
Premature bolting, which causes lettuce to form a flower stalk and become bitter tasting, is a common problem in hot weather. Use these bolting prevention tips:
- Consistent moisture and optimal temperatures discourage early bolting.
- Avoid planting lettuce in very warm microclimates next to concrete or brick walls.
- Cut (rather than pull) lettuce heads just above soil level to harvest, leaving the roots intact.
- Use shade cloth, row cover and mulch as needed to maintain cooler soil temperatures.
- Prioritize lettuce varieties specifically bred for heat tolerance and slow bolting.
- Sow successively maturing varieties to ensure a constant supply.
Grow Lettuce for Microgreens
Microgreens are immature greens harvested when just 1-3″ tall. They are more bolt resistant than full size lettuces:
- Growing lettuce for microgreens allows harvest in as little as 2 weeks.
- Use shallow trays filled with seed starting mix. Sow seeds thickly.
- Keep soil moist and avoid hot sun. Harvest microgreens when first true leaves appear by cutting just above soil.
- Lettuces like green leaf, red leaf, oakleaf green and red are all excellent microgreens.
- Microgreens offer an intense burst of flavor and can be cut fresh as needed.
Try Hydroponic or Container Production
Growing lettuce hydroponically or in containers allows greater control over soil moisture and temperature:
- Move container plants into dappled shade locations to reduce excessive heat gain.
- Adjust formulas or reservoirs to keep water supply consistent for hydroponics.
- Opt for lettuce varieties bred for hydroponics and containers like green romaine, red romaine, green leaf and red leaf.
- Monitor plants closely and harvest as soon as ready since enclosed areas heat up quickly.
- Use reflective mulches like aluminum-coated plastic in containers to repel heat buildup.
Harvest Lettuce Early in the Morning
For the highest quality lettuce in hot conditions, harvest first thing in the morning while temperatures are coolest:
- Plants will be fully hydrated and most crisp early in the day.
- Use a sharp knife to cut heads 2″ above soil level or cut individual leaves just above the crown.
- Chill lettuce immediately in ice water for 15-20 minutes post-harvest to maintain freshness.
- Take advantage of cool mornings to harvest heat-sensitive varieties even if not fully mature.
Morning harvests will yield the freshest, crispest lettuce for summer salads and sandwiches. Proper timing, preventative measures and care can help you beat the heat and keep lettuce growing successfully even during hot summer months. With the right strategies, fresh homegrown lettuce can be on the menu all season long.
Frequently Asked Questions About Growing Lettuce in the Heat
Growing tasty lettuce in the peak of summer is challenging but possible with the right approach. Here are answers to some common questions about handling hot weather lettuce cultivation:
What causes lettuce to bolt in hot weather?
Lettuce is triggered to bolt (send up a flowering stalk) by a combination of warm weather and long daylight hours. Temperatures above 75°F, especially at night, often prompt premature bolting.
Should lettuce be kept moist in summer?
Yes, consistent soil moisture is very important to prevent wilting, bitterness, and bolting in heat. Use mulch and irrigation to maintain moist soil. Avoid watering foliage in midday sun.
What is the ideal temperature range for lettuce?
Lettuce grows best in cool conditions, ideally with average temperatures between 60-70°F during the day and 45-55°F at night. Temperatures above 80°F will cause problems.
Should lettuce be grown in full sun during summer?
No, partial shade is ideal to prevent excess heat. Filtered sunlight under taller plants or shade covers is optimal for lettuce in hot conditions.
When is the best time to plant lettuce for fall harvest?
Start lettuce for fall about 6-8 weeks before your first expected autumn frost. Choose faster-maturing varieties suited to cool conditions.
How can I prevent lettuce from bolting too early?
Choose inherently slow-bolting varieties, avoid heat pockets near warm walls, use shade covers to reduce heat and sunlight, ensure adequate moisture, and harvest heads promptly.
What lettuce varieties are most heat tolerant?
Oakleaf, Latin, mini romaine, and summer bibb lettuces generally have the best heat tolerance. Seek out newer varieties bred specifically for warm conditions.
Should I harvest lettuce in the morning or evening during summer?
Always harvest lettuce in early morning hours before the day heats up. This ensures the highest moisture content, crispness, and flavor quality.
Conclusion
Growing lush, crisp lettuce throughout hot summer months is certainly possible, even though it can be challenging compared to cooler times of year. Keys to success include selecting the most heat tolerant lettuce varieties, carefully timing plantings, providing adequate shade and moisture, and planning for morning harvests while temperatures are cool. With some added attention, fresh homegrown lettuce can be enjoyed as a summertime treat. Follow this guide and don’t let the heat stop your lettuce harvesting until fall arrives again.