Lettuce is a popular, fast-growing vegetable that thrives in cool weather, making it a garden staple for spring and fall harvests. Because the plant develops a shallow root system, the depth at which it is planted is a critical factor for successful growth. A slight error in planting depth can easily prevent germination or cause a fragile young plant to rot. Understanding the specific requirements for both seeds and transplants ensures the lettuce can establish itself quickly and produce crisp, tender leaves.
Planting Depth When Starting from Seed
Lettuce seeds require an extremely shallow planting depth, often overlooked by new gardeners. The tiny seeds should be covered with only 1/8 to 1/4 of an inch of fine soil or vermiculite, just enough to maintain moisture contact. Planting the seeds too deeply is the most common reason for germination failure, as lettuce seeds are photoblastic, meaning they require light to sprout.
The optimal soil temperature range for germination is cool, typically between 55°F and 65°F. Temperatures above 75°F cause the seed to enter thermal dormancy. This sensitivity, combined with the need for light, dictates the shallow planting method. Gently firming the soil after sowing ensures good seed-to-soil contact.
Planting Depth for Seedlings and Transplants
When planting lettuce started indoors or purchased as a transplant, the goal is to disturb the plant as little as possible while maintaining the existing soil line. The young plant should be set into the garden bed at the exact same depth it was growing in its nursery pot. The top of the root ball should be flush with the surrounding garden soil.
Avoid burying the crown, the point where the stem meets the roots, as this area is susceptible to rot if kept constantly moist. Conversely, planting too shallowly exposes the fragile upper roots to air, causing them to dry out and stress the plant. Carefully backfill the hole and lightly press the soil around the root ball to secure the transplant.
Ensuring Proper Spacing and Arrangement
Once the correct depth is achieved, proper spacing is necessary to ensure adequate light penetration and air circulation. This helps prevent fungal diseases and delays premature bolting in warmer weather. The required distance between plants varies significantly depending on the type of lettuce being grown.
Spacing Requirements
Loose-leaf varieties, often harvested using the “cut-and-come-again” method, require the least space and can be planted 4 to 6 inches apart. Larger, head-forming types like Romaine, Bibb, or Butterhead need 8 to 12 inches to mature fully. Crisphead varieties, such as Iceberg, demand the most space, needing up to 16 inches between each plant to develop their dense heads.
Immediate Post-Planting Care
The first steps after planting focus on helping the seeds or transplants establish themselves. Immediately after planting, a gentle and thorough watering is necessary to settle the soil around the roots and eliminate air pockets. The soil must be kept consistently moist but never waterlogged; a light, frequent watering schedule is better than deep, infrequent soaking.
If starting from seed, thinning must occur once the seedlings develop their first true leaves and reach about two inches in height. This involves removing the excess plants to achieve the final desired spacing, redirecting available resources to the strongest remaining seedlings. Thinned plants can be transplanted or harvested as tender microgreens.