Lettuce is a popular cool-season vegetable, and every variety, belonging to the species Lactuca sativa, begins its existence as a small seed. This process is fundamental to its biology, whether the seeds are sown directly into the garden or started indoors. This article explores the biological journey of the lettuce plant and provides steps for successfully growing it from its initial seed state to maturity.
The Lifecycle of Lettuce: From Seed to Seed Production
The lifecycle of lettuce begins when the seed absorbs water and germinates, first pushing out a root (radicle), followed by seed leaves (cotyledons). The plant then develops true leaves and enters the vegetative phase, focusing energy on creating the rosette or head of leaves. This leaf production period lasts 30 to 75 days, depending on the variety.
Reproduction is triggered by environmental cues like increasing heat and longer daylight hours. When these conditions are met, the plant initiates bolting, rapidly sending up a central flower stalk. Bolting switches the plant from vegetative growth to its reproductive phase, causing the leaves to become tough and develop a bitter flavor.
Once the flower stalk is extended, the plant produces small, self-pollinating, yellow flowers. These flowers mature and dry, forming small, elongated seeds. Each seed is attached to a feathery structure that aids in wind dispersal, completing the progression from seed to seed.
Essential Steps for Successful Seed Germination
Starting lettuce from seed requires careful attention to environmental factors, particularly temperature. The ideal range for germination is cool, between 15°C and 20°C (60°F and 70°F). If soil temperatures exceed 25°C, the seeds may enter thermodormancy, preventing them from sprouting.
Sow the tiny seeds shallowly, covering them with only 3 to 6 millimeters (1/8 to 1/4 inch) of fine soil. Lettuce seeds have a light requirement for germination, meaning they should not be buried deeply. The soil must be light, loose, and consistently moist, as steady hydration is necessary to initiate the process.
Maintaining a cool and damp seedbed is the most important factor for success. If high temperatures are expected, starting seeds indoors or in a shaded area helps bypass heat-induced dormancy. Once seedlings emerge, they require consistent light; inadequate light can cause them to become elongated and weak.
Starting Lettuce Without Seeds: Transplants and Timing
While direct seeding is common, gardeners often use small, established plants known as transplants to bypass the sensitive germination phase. Transplants, typically bought from a nursery, offer a head start, reducing the time the crop occupies the garden space. This approach is useful for achieving a uniform stand and an earlier harvest, often shortening field time by several weeks.
The choice to use transplants is tied to seasonal timing, which is the primary factor for growing lettuce. As a cool-weather crop, lettuce thrives when planted in early spring or late summer and fall, allowing it to mature before summer heat arrives. Planting during these shoulder seasons helps avoid high temperatures that trigger premature bolting or cause germination failure.
Using an established plant sidesteps the risk of thermodormancy and ensures the plant is large enough to compete with weeds. This allows the plant to focus immediately on producing edible leaves during its preferred cool period.