How does temperature affect lettuce planting?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Temperature has a tremendous effect on lettuce growth from seed to harvest. Germination is achieved with soil temperatures between 40-80°F (4-27°C), whereas optimal growth occurs between 60-65°F (16-18°C) temperatures below 40°F (4°C) slow growth and row cover becomes necessary. Temperatures above 75°F (24°C) will require shade cloth to reduce bitterness, and bolting occurs quickly at temperatures above 85°F (29°C).
Cold Protection
- Install row covers when temperatures drop below 40°F (4°C)
- Use cold frames to extend spring planting by 3 weeks
- Water soil before frost events for thermal insulation
- Select frost-tolerant varieties like Winter Density
Heat Mitigation
- Deploy 40% shade cloth above 75°F (24°C)
- Water deeply at soil level during early morning
- Use reflective mulches to reduce soil temperature
- Switch to bolt-resistant varieties like Jericho Romaine
Use a probe thermometer to monitor soil temperature before planting. Cold soils slow down germination, while warm soils lead to poor seedling growth. For spring planting, wait until the soil temperature is 45°F (7°C). In the fall, plant when the soil temperature is below 70°F (21°C) and record daily high and low temperatures to observe patterns.
Effectively manage your microclimates. Southern exposures will warm faster in the spring, while northern ones will remain cooler for longer. I like to use thermal mass, such as stone borders, to collect heat during the day. Use screens or burlap to break the wind. The most effective method is to place containers on gravel to cool the root zone. All of these methods extend the growing period of your container gardening by 4 to 6 weeks.
Identify bolting Indicators: elongated central stems, bitter tasting, and loose leaf formation. Harvest immediately as soon as bolting starts because quality deteriorates quickly. Prevent future bolting by planting varieties that resist bolting and keeping consistent moisture. Schedule plantings to miss peak summer heat.
Adapt your practices according to local conditions. Coastal gardens require less heat protection than inland gardens; mountain locations require different plant dates, while desert regions benefit from double shade cloths. Track local weather patterns with simple max-min thermometers. Just one season of observation will lead you to the ideal planting dates.
Read the full article: When to Plant Lettuce: Ultimate Growing Guide
