Growing Lettuce at Home
When lettuce is mentioned, many people think of the standard iceberg lettuce found in supermarkets and restaurant salads. But that is changing quickly with the growth in popularity of different types of lettuces, mainly due to the flavors and colors that they offer. When you’re growing lettuce from seed at home, you can choose from the full spectrum of seed that’s available.
At farmers markets, health food coops, and organic food stores, a big variety of lettuce types have cropped up. Their colors range from deep red to mottled greens, all the way to almost white. And their flavors vary from noticeably sweet to tangy, and slightly bitter.
Iceberg lettuce, originally bred as a hybrid, is now offered as open pollinated varieties and has been around long enough to be considered by some as an “heirloom”!
Eating with the Seasons
We have come to expect lettuce year round. We’ve been educated by the supermarkets about what our vegetables should look like, what they should taste like, and when they should be available. And for most of them, we expect them to be available all year.
Many people are surprised to learn that lettuce is a cool-season crop. It will bolt, or go to seed, readily during late spring and early summer months.
Where I live, it is best to plant lettuce early in the spring and then again in late summer or early fall when the temperatures start to cool off.
Infographic: Save Our Seeds
Better Lettuce Seed Germination
Lettuce seeds won’t sprout when soil temperatures are above 80° F. But they will start to germinate as low as 40°F, making it ideal for early- and late-season planting.
When temperatures are too high, a plant hormone is produced that stops the germination process. This is called thermo-inhibition. This trait is a carryover from wild lettuce that originated in the Mediterranean Middle East, where summers are hot with little moisture. If the lettuce seeds were to sprout under these conditions, they would soon die out and the species would go extinct.
Choose Heat-Resistant Lettuce
Thanks to traditional plant breeding, several varieties of lettuce have been selected for heat-tolerant characteristics. And some of these are open-pollinated, meaning you can save the seeds from year to year.
Some examples are Saint Anne’s Slow Bolting, Summertime, Black Seeded Simpson, and Jericho. Just because these are heat tolerant doesn’t mean that they will grow through the summer. It only means that they won’t bolt or turn bitter quite as quickly.
Growing Lettuce from Seed: Tips & Tricks
Thanks to ongoing research on lettuce traits, there are some techniques home gardeners can use to extend the sprouting for lettuce seeds into the warmer months. The optimum soil temperature for most lettuce seeds is 68°F, with some varieties sprouting in the 40-75°F range. The temperature of the soil must be taken—not just the air temperature, which can be several degrees different.
Imbibing or soaking the seeds in cool water for 16-24 hours in a well-lit area before planting will increase the germination percentages greatly. Red light has been found to be the best color, but if you don’t have access to a non-heating red light, sunlight or full-spectrum light was found to be almost as good. In warm conditions, soaking the seeds in the dark can actually decrease their germination rates. And soaking for less than 16 hours has little to no positive effect on germination rates.
Extending the Lettuce Season
Successful methods of extending the season for lettuce in the garden include laying a thick mulch of straw or wood chips on the ground at least 1 1/2 to 2 inches deep. This insulates the soil from becoming too hot and helps to preserve moisture in the soil.
Lightly shading the lettuce plants can provide enough of a temperature drop to keep them from bolting, sometimes up to 3-5 weeks. Shade can be from a shade cloth or a row cover on a low tunnel, or by companion planting tall, wide-leafed plants such as some types of pumpkin.
The traditional rule of thumb of “plant early and plant often” can be adjusted for lettuce as “plant late and plant often.” When temperatures start to drop, be ready to start more lettuce seed for a second harvest in the fall.
(This article was originally published May 22, 2014.)