Lettuce is a cool-season crop that requires full sun. Full sun is defined as at least six hours of sun a day, but preferably more. Although lettuce requires full sun, it is also tolerant of partial shade. It can grow well with approximately four to six hours of direct sunlight on the low end.
Despite the fact that lettuce thrives in full sun, it does better with some shade during the summer months. Although lettuce can grow in partial shade, it cannot grow in full shade.
If lettuce gets too much sun during hot weather months the plant will begin to bolt, wither, or die.
Bolting is a stress-response that occurs in plants, causing them to flower early which diverts energy from growth of the leaves and causes the leaves to taste more better.
Slow-bolting or heat-resistant varieties (e.g., oak-leaf types) are available and are recommended for extending the lettuce-growing season.Lettuce – University of Maryland Extension
While it is not recommended, it is possible to grow lettuce in hot weather. There are certain varieties of lettuce which are more heat-resistant and are often referred to as summer lettuce.
To protect lettuce from extreme heat, consider planting lettuce alongside crops such as tomatoes, corn, or pole beans, which will provide the lettuce plant with shade when they get bigger.
Mulch on top of soil, shade cloths, and more frequent watering can help keep lettuce cool during hot weather.
Does Lettuce Require Full Sun?
Lettuce is a crop that prefers full sun during the spring and fall, but is tolerant of partial shade and actually prefers it during summer months.
Different plants require different levels of exposure to the sunlight. For a crop that requires full sun, that plant must receive six to eight hours of direct sunlight between the hours of 10 a.m. and 4 p.m.
All types of lettuce (crisphead, butterhead, leaf or bunching, and romaine or cos) require cool, moist growing conditions. Daytime temperatures of 70 to 75 and nighttime temperatures of 55 to 60 are ideal.Lettuce – Iowa State University Extension and Outreach
It is suggested that lettuce be planted in the early spring in full sun to encourage rapid growth. Additionally, consider planting lettuce amongst other crops such as corn, tomatoes, or pole beans, which will offer lettuce shade during the summer.
Since lettuce does require some exposure to shade during the hot summer months, companion planting with taller crops will provide lettuce with the shade it needs in the heat, while still offering direct sunlight in the spring.
Can Lettuce Grow in the Shade?
While lettuce does require a minimum amount of shade, it can only tolerate partial shade. In general, lettuce needs full sun, at least 6 hours a day, during the brightest hours of the day. Partial shade is slightly less than full sun, requiring four to six hours of direct sunlight a day.
In essence, lettuce is unable to grow in full shade. Lettuce can be exposed to the shade during the spring and fall, but requires full sun. However, it is important that lettuce receives shade during the summer, so consider planting lettuce with taller crops or small trees.
What Happens When Lettuce Gets Too Much Sun?
If lettuce receives too much sunlight the leaves can wither and become bitter tasting and the plant becomes highly susceptible to bolting. Bolting is a phenomenon that occurs in plants and is a reaction to stress. Bolting is a premature formation of flowers and seeds that significantly alter the harvest.
If bolting occurs in lettuce, it affects the taste of the crop, resulting in bitter and tough leaves. Bolting is common in lettuce, and is caused by stressful factors such as high temperatures, extended periods of time in the sun, or drought.
Lettuce goes through four growing phases; juvenile/vegetative, adult/vegetative, intermediate/vegetative, and adult/reproductive. When lettuce is in the vegetative state, it is more adapted to handle environmental stresses. However, when lettuce reaches the intermediate level, it becomes more susceptible to harsh environmental conditions, which will lead the plant to bolt.
How To Grow Lettuce in Hot Weather
In order to grow lettuce in hot weather, it is important they receive enough moisture. Lettuce is a heavy-feeding plant with a shallow root system, so to encourage consistent growth, ensure the plant receives sufficient amounts of water.
However, since lettuce is not generally tolerant to high temperatures, growing lettuce in hot weather may create a bitter taste in the leaves or cause the plant to go to seed, bolt.
Another way to grow lettuce in hot weather is to seek out heat-tolerant varieties of the crop. Some examples of heat tolerant lettuce are Amish Deer Tongue lettuce, Royal Oakleaf lettuce, and Bergamo lettuce.
These varieties, which are more heat-tolerant than their cool-season counterparts, are often referred to as summer lettuce.
Although it is possible to grow lettuce in hot weather, by choosing proper varieties or providing adequate growing conditions, it is not preferred. Lettuce is a cool-season crop, often planted in early spring or fall because of its intolerance to extreme temperatures.
If lettuce is exposed to too high of temperatures it can cause the leaves to wither and taste bitter or cause the plant to bolt, which does the same resulting in a lower quality crop or the complete loss of the crop.
Please comment below with your own thoughts and experiences with growing lettuce.