When To Grow Lettuce
Although lettuce grows most easily in cool weather, most varieties can be encouraged to produce even in the summer. To enjoy fresh lettuce from spring through fall, keep planting new crops about every 3 or 4 weeks. Each season has its own cultural requirements, so select lettuce varieties that are adapted to the changing temperatures.
Spring - The easiest time to grow lettuce is in the spring. Even little lettuce seedlings can handle light frost. Plant lettuce seed right out in the garden as soon as the ground is no longer frozen. Seeds will germinate when the soil temperature is as low as 45° F. Seedlings purchased from the garden center or grown indoors can go in the ground a week or so before the last expected spring frost in your area. Good spring varieties include ‘Deer Tongue’ (looseleaf), ‘Amish Winter Lettuce,’ ‘ButterKing,’ ‘Red Oak Leaf,’ and ‘Cocarde.’
Summer - Many lettuce varieties, when exposed to hot dry weather with no protection, turn bitter and bolt or go to seed. For the warm weeks of late June, July, and August, protect lettuce plants from the sun or plant warm weather varieties. Shade plants with shade cloth, garden fleece, cheesecloth, lath, or other shading material. Or plant them in the afternoon shadow of taller plants or trellised crops. ‘Oak Leaf’ is one of the most heat resistant varieties of leaf lettuce. Other summer varieties include ‘Capitane,’ (butterhead), ‘Jericho,’ (Romaine), and ‘Vanity’ or ‘Summertime’ (crispheads).
Fall - Start a crop of lettuce for fall harvest in August. Shade new seedlings from the late summer heat, and then, as the fall gets colder, remove the shading so they get good sun and set up a shelter from the frost. Protect mature producing plants with a cold frame or protective covering material such as white, polyspun row covers of garden fleece. Fall season lettuces include ‘Marvel of Four Seasons,’ (butterhead), ‘Romance’ (Romaine), and ‘Canary Tongue’ (looseleaf).
Where To Plant Lettuce
Unlike most vegetables, leaf lettuce can tolerate some shade, as little as just 5 hours of sun daily. In fact, during the hot summer months, lettuces require shade in the middle of the day. Too much heat causes them to turn bitter and “bolt,” or go to seed.
Plant looseleaf and butterhead lettuce either in single rows, in wide “bands” 3 or 4 plants across, or scattered among other plants in the vegetable bed or even in the flower bed. Use looseleaf types as a colorful border around flower or herb gardens, alternating red lettuce and green lettuce for a decorative effect. As for all plants, good soil with plenty of organic matter worked in is ideal for lettuce because the roots can grow 18 to 36 inches deep, enough to reach sufficient moisture if drought threatens.
How To Plant Lettuce
There are several ways to plant lettuce. The easiest way is to plant professionally raised seedlings available in garden centers and nurseries in early spring. Typically, varieties are offered that do well locally, but the assortment is usually not very broad, so choices of lettuce types are limited. If you plant seedlings, you won’t have to thin the plants later, so there is no waste and less work. Begin transplanting them outdoors about a week before expected last frost at the earliest, spaced about 6 to 8 inches apart.
Planting lettuce seeds gives you many more choices, as mail order catalogs abound with many tempting varieties of each lettuce type. Plant seeds directly into the garden bed when the soil has thawed and dried out so that it can be easily worked. An alternative is to start seeds indoors several weeks prior to the last frost in your area and then transplant them outdoors into prepared beds. For a steady supply of lettuce, continue to start seedlings every few weeks and plant them outside periodically throughout the spring. Seedlings should be ready to harvest about 3 to 5 weeks after being set out. Lettuce does not compete well with weeds, so keep rows or beds well cleared.
To transplant seedlings into the garden, follow these steps:
1. Plant lettuce seedlings on an overcast day, or late in the afternoon to reduce their exposure to hot sun while they recover from transplant shock. Wait until the soil is fairly dry and can be dug without making sticky clumps of soil. Prepare the planting area by digging into the soil from 6 to 8 inches deep with a trowel or shovel. Turn over the soil to loosen it, breaking up any clumps and removing rocks and debris. This is a good time to sprinkle some all-purpose, slow-acting granular fertilizer on the soil and mix it in. Smooth and level the planting area.
2. Water the plants well 1 to 2 hours before setting them out. Dig holes in the planting bed about 6 inches apart and about as deep as the containers holding the lettuce seedlings. Tip the seedlings gently out of their little pots and set each plant in its hole. Set plants deep enough in the holes to cover the stems up to the first set of true leaves, and firm the soil around them. This helps ensure that the plants will stay upright when watered.
3. Water the plants to settle the soil around the roots. If you have put all-purpose fertilizer in the soil already, do not fertilize the seedlings further at this time. Adding some seaweed or kelp-based tonic to the water when you water them in helps ease transplant shock and get the seedlings off to a good start is a good idea, but it no necessary.
To start lettuce directly from seed in the garden, follow these steps:
1. Prepare the soil as for seedlings described above.
2. Trace a shallow indentation in the soil with a stick or pencil to guide planting. Then sow the seeds by dribbling them through your thumb and forefinger into the indented rows. OR, scatter the seeds over the designated area. Cover them with a thin layer of soil, sand, vermiculite or peat moss mixed with a little soil so that they are only about 1/4 inch deep. They will germinate as long as the soil temperature is as high as 45° F.
3. Since the goal is to have lettuce plants that are 6 to 8 inches apart, you will have to pull out, or thin, the crowded new sprouts up (thin) a few times as they grow increasingly mature, to arrive at this spacing. These tiny, tender sprouts are a special treat in a salad. Pinch or rinse off their wispy roots, and serve. Do not omit this thinning process, as lettuce plants grow poorly when they are crowded. Another way to assure evenly spaced plants is to use seed tapes, in which the seeds are embedded at the correct spacing into a paper tape, suitable for planting directly into the soil. Plant the tape in one long row or tear it into pieces to fit a few lettuces in among other plants.
Starting Your Own Seedlings Indoors
1. Sow lettuce seed indoors about 4 to 6 weeks before the last expected frost in your area. Plant 2 or 3 seeds into small peat pots filled with soilless potting mix or other sterile growing medium.
2. Cover the seeds with about 1/4 inch of the potting mix. Expect seeds to germinate in 2 to 10 days, depending on the room temperature. Newly germinated seeds do best in-doors under adjustable fluorescent lights, constantly adjusted to set about 1 inch above the plants as they grow. The seedlings should get 14 hours of light per day. Seedlings started indoors will be ready to set outside in 2 to 3 weeks.
Holding Overeager Seedlings: If your seedlings are ready to transplant before weather and soil conditions are appropriate, store them for up to 2 weeks in the refrigerator at about 34 °F. Keep their soil moist. The plants stop growing, but are not harmed.
Chill seeds for summer planting: Here’s one way to keep lettuce coming through the summer months. Mix the lettuce seeds with equal amounts of dampened sand and peat moss and put the mixture in the refrigerator for 4 to 5 days, then plant them as soon as you get them out of the fridge. Water the rows or beds with cold water daily for a week, to keep the soil temperature down.
Lettuce Lovers Alert: All cole crops, such as broccoli, kale, collards, and cauliflower, leave a chemical residue in the soil called thiocyanate. This natural substance protects these plants from soil- dwelling insects and weeds. It also inhibits germination of any seeds, including lettuce seeds planted nearby during the season. However, by the following season, the thiocyanate breaks down and is no problem. Lettuce seedlings are not affected by residues from cole crops.
Amendments In Planting or Transplanting
There are a number of products at the garden center that will help your newly planted or transplanted plants deal better with the stress inherent in the planting process. All healthy plants have beneficial fungi, called mycorrhizal fungi, living on their roots. You can buy these valuable additions to your plant’s ecosystem. See the file describing Using Micorrhizae When Planting.
In addition, there are a number of products such as seaweed, compost tea, and beneficial soil microbes that when added to the planting process will help your newly established plants get going faster. See the file New Technology In Plant Growth Activators
Lettuce In Containers
Lettuce grows well either alone or combined with other plants in containers of all kinds, including window boxes. The various colors and textures of looseleaf types make attractive features on decks and patios. While most any variety of lettuce thrives in this situation, the butterhead variety ‘Tom Thumb’ is especially suited for container growing because of its compact size. ‘Bibb’, ‘Buttercrunch’, and ‘Dark Green Boston’ are also good. The best container for lettuce is 12 inches wide and at least 8 inches deep to encourage healthy root development. Be sure it has a drainage hole. Plants in stress-prone locations such as a patio exposed to warm, drying winds, or in an elevated location, may need a slightly larger container than plants that are less exposed. Use a soilless mix and water often to assure that the container never gets dried out.