Lettuce is a rewarding crop for beginning gardeners, known for its fast growth cycle and relative ease of cultivation. This leafy green offers a wide range of types, including butterhead, loose-leaf, romaine, and iceberg. Growing lettuce from seed is an accessible way to enjoy a continuous supply of fresh greens, provided you understand its cool-season nature. A successful harvest requires careful attention to the growing environment and proper sowing techniques.
Preparing the Planting Environment
Lettuce is a cool-weather crop, so the optimal time for planting is early spring and fall, avoiding the extreme heat of mid-summer. The ideal growing temperature range is between 60 and 65 degrees Fahrenheit. Spring planting can begin as soon as the soil is workable, typically two to three weeks before the last expected frost date.
Site selection should prioritize full sun in cooler climates. However, partial or afternoon shade is best where temperatures regularly exceed 75 degrees Fahrenheit. Lettuce appreciates fertile, well-drained soil rich in organic matter, such as compost, which helps maintain consistent moisture retention. The soil pH should range between 6.0 and 7.0 to ensure proper nutrient uptake.
Sowing Techniques for Optimal Germination
Lettuce seeds can be started indoors for an early harvest or direct-sown into the garden bed. Starting seeds indoors four to six weeks before the last frost allows a head start, particularly for head-forming varieties like romaine or butterhead. For indoor starts, use shallow trays filled with a sterile, light seed-starting mix, ensuring the mix is thoroughly moistened before sowing.
Lettuce requires light to germinate, making it a “light germinator.” Consequently, the seeds should be sown very shallowly, only about 1/8 to 1/4 inch deep, or lightly covered with a thin layer of soil or vermiculite. Planting too deeply prevents light from reaching the seed and reduces the germination rate. Optimal soil temperatures for germination are cool, ideally between 55 and 65 degrees Fahrenheit, as temperatures above 75 degrees Fahrenheit can induce thermal dormancy, causing the seeds to fail.
When direct-sowing outdoors, create shallow furrows or broadcast the seeds thinly over a prepared area. For full-sized heads, space the rows about 12 to 18 inches apart. For a continuous supply of baby leaves, broadcast the seeds more densely and plan to harvest leaves while they are small. Gently press the soil down after sowing to ensure good seed-to-soil contact, which aids in moisture absorption and germination.
Post-Planting Care and Thinning
Immediately following planting, the seedbed must be kept consistently moist but not waterlogged to support the delicate germination process. Use a fine mist spray or a watering can with a gentle rose attachment to prevent washing away the shallowly planted seeds. Consistent moisture is necessary because the shallow planting depth leaves the seeds and emerging roots vulnerable to drying out quickly.
Once seedlings emerge and develop their first set of true leaves, thinning is necessary to ensure a healthy, mature crop. Thinning involves removing excess seedlings to provide adequate space for the remaining plants to grow to their full potential. This prevents competition for light and nutrients, as overcrowding can lead to stunted growth and increased disease risk.
The final spacing depends on the variety: loose-leaf types typically need about 4 inches between plants, while romaine and butterhead need closer to 8 inches. Thinning is best done when the soil is damp, carefully pulling the smaller or weaker seedlings to avoid disturbing the roots of the keepers. Thinned seedlings can often be consumed as microgreens or carefully transplanted to another area if the roots remain intact.