Starting lettuce seeds indoors gives this cool-season crop a significant advantage, allowing for an earlier harvest before summer heat causes the plants to bolt or turn bitter. Seedlings are typically grown in small trays or containers where conditions are precisely controlled, protecting the young plants from harsh outdoor elements. Transplanting them to a permanent garden location maximizes their growth potential and overall yield. Success depends on accurately judging the plant’s physical maturity and ensuring the outdoor environment is ready for the transition.
Identifying the Right Time to Move Seedlings
Determining the precise moment for transplanting involves checking both the plant’s physical development and the outdoor soil conditions. Seedlings are generally ready for the move when they are between four and six weeks old, having established a robust root system. The most reliable physical indicator is the presence of four to six true leaves, which appear after the initial cotyledon leaves. Transplanting too early can lead to shock, while waiting too long can result in the plants becoming root-bound and stunted.
Lettuce is a cool-weather crop, requiring the garden soil to be environmentally ready for a smooth transition. The soil temperature should ideally be in the range of 45°F to 65°F for the roots to establish and grow actively. A slightly warmer temperature is preferred for transplanted seedlings, even though seeds can germinate in soil as cool as 40°F. Moving the plants outside should only happen when the danger of a hard frost has passed, though properly acclimated seedlings can tolerate temperatures as low as 20°F.
Preparing Seedlings for the Outdoors
The pre-transplant process known as “Hardening Off” conditions indoor-grown seedlings for the outdoor environment. This gradual acclimation is necessary because the tender foliage is unaccustomed to direct sunlight, wind, and temperature fluctuations. Without this step, plants can suffer severe stress, leaf burn, or even death from transplant shock.
This hardening process should begin about seven to ten days before the intended transplant date. Start by placing the seedlings outdoors in a sheltered, shaded location, protected from strong winds, for just one to two hours. Gradually increase the duration of their outdoor exposure daily, monitoring the weather for extremes. After a few days, introduce the plants to direct sunlight, starting with the gentler morning sun for short periods. The goal is to have them tolerate longer periods of sun and wind exposure, eventually remaining outside overnight if temperatures are mild.
Techniques for Successful Transplanting
The physical act of transplanting should be executed with care to minimize disturbance to the plant’s root system. The best time of day for the move is late afternoon or on a cloudy day, allowing the seedlings to acclimate overnight without the stress of intense midday sun. Before removing the seedlings from their trays, ensure the soil is moist but not waterlogged, which keeps the root ball intact and reduces crumbling.
When planting, handle the seedlings by their leaves or root ball rather than the stem. The planting depth should be the same as the depth they were growing in their original container; burying the stem too deep can encourage rot. Dig a hole slightly wider than the root ball, gently place the seedling, and firm the soil around it to eliminate air pockets.
Proper spacing in the garden is necessary for air circulation and growth, varying by lettuce type. Loose-leaf varieties can be planted closer, about 4 inches apart, while head-forming types like Romaine or Butterhead require 8 to 12 inches between plants. Immediately after transplanting, provide a thorough, deep watering to settle the soil around the roots and reduce the risk of transplant shock. If the sun is unexpectedly intense following the move, a temporary shade cover can provide a brief reprieve until the plants are established.