Lettuce is a cool-season crop, meaning it thrives in the mild temperatures of early spring and fall, but struggles in the heat of summer. Starting lettuce indoors as seedlings and then transplanting them outside allows for an earlier harvest and extends the growing season. Successfully moving these young plants to the garden requires careful timing and preparation. The goal is to minimize the shock of the transition, giving the seedlings the best chance to grow into robust, mature plants.
Determining the Optimal Time for Transplant
The primary factor in timing the transplant is the average last expected frost date for your region. Lettuce seedlings are cold-tolerant and can typically be moved outdoors safely about three to four weeks before this date. This early timing allows the plants to mature during the spring’s cooler weather before temperatures rise too high, which can cause the lettuce to bolt, or prematurely produce a seed stalk.
Lettuce grows best when the air temperature is consistently in the 60°F to 65°F range. The soil temperature is also a significant indicator of readiness.
The ideal soil temperature range for transplanting lettuce is between 55°F and 65°F. You can monitor this by inserting a soil thermometer a few inches deep into the garden bed. Transplanting when the soil is too cold can stunt the plant’s growth, and planting too late encourages bolting and bitterness in the leaves.
Acclimating Seedlings Through Hardening Off
Seedlings grown indoors are accustomed to a controlled environment, making them soft and vulnerable to outdoor elements like direct sun, wind, and temperature shifts. The process of “hardening off” gradually toughens the plant tissue, preparing it for the rigors of the garden. This acclimation should be done over a period of seven to fourteen days before the planned transplant date.
Begin the process by placing the lettuce seedlings outside in a shaded, protected spot for one to two hours on the first day. The goal is to introduce them to the outdoor temperature and air movement without the stress of intense light. Over the following days, the time spent outdoors is gradually increased, and the plants are moved into areas with more direct sunlight.
By the end of the hardening-off period, the seedlings should be able to remain outside for most of the day, including a few hours of direct morning sunlight. This slow introduction prevents leaf burn and transplant shock, enabling the plants to develop stronger stems and a thicker cuticle layer for protection. Slightly reduce the frequency of watering during this period, but never allow the plants to completely wilt.
The Step-by-Step Transplanting Process
Transplanting is best done in the late afternoon or on a cloudy day, which minimizes the initial stress from intense sunlight and heat. Before planting, the garden bed should be prepared by loosening the soil and incorporating a generous amount of organic matter, such as compost, to ensure good fertility and drainage. Lettuce is a shallow-rooted crop, so the soil should be friable to a depth of at least six to eight inches.
When removing the seedlings from their containers, handle them gently by the root ball or the leaves, avoiding any pressure on the delicate stem. Plant the seedlings at the same depth they were growing in their original cell or container, ensuring the base leaves sit just above the soil surface. Planting too deep can cause the stem to rot.
The spacing between plants will vary based on the type of lettuce. A general guideline is to allow about 8 to 10 inches between leaf lettuce plants and 10 to 12 inches for head-forming varieties like Romaine or Butterhead. Adequate spacing is important for air circulation, which helps prevent fungal diseases. After placing each seedling in its hole, gently firm the soil around the root ball to eliminate any air pockets.
Immediate Post-Transplant Care
Immediately following the transplant, the seedlings require a thorough, deep watering to settle the soil around the newly placed roots and rehydrate the plant. This initial watering is crucial for establishing root-to-soil contact, which is necessary for the plant to begin absorbing nutrients and moisture. The soil should be consistently moist, but not saturated or soggy, as lettuce does not tolerate waterlogged conditions.
For the first few days, monitor the plants closely for signs of transplant shock, which often appears as wilting or drooping leaves. If the weather is unexpectedly hot or sunny, providing temporary shade, such as a row cover or a piece of cardboard, can help reduce water loss and stress on the tender foliage. Avoid applying any fertilizer immediately after transplanting, as this can burn the roots; wait until the plant has fully recovered and resumed active growth before considering a light feeding.