Romaine lettuce, known for its crisp texture and tall, upright heads, is a nutritious vegetable that thrives in the home garden. Starting this cool-weather crop from seed is a straightforward process that allows gardeners to cultivate many plants for a continuous harvest. The success of growing Romaine hinges on timing the planting correctly and providing consistent care through the early stages of growth.
Selecting the Best Time and Site
Romaine lettuce is a cool-season annual, meaning it performs best when temperatures are moderate, typically between 45°F and 75°F. Planting is best done in early spring as soon as the soil is workable, or in the late summer for a fall and winter harvest. For a spring crop, sowing seeds about two to three weeks before the last expected frost date is ideal, as the seeds can germinate in soil temperatures as low as 40°F. Conversely, fall planting should occur roughly eight weeks before the first expected hard frost.
The chosen site should receive full sun, which is about six hours of direct sunlight daily, though Romaine will also tolerate partial shade, especially in regions with intense afternoon heat. Providing some afternoon shade helps prevent the plant from bolting, which is when the lettuce prematurely produces a flower stalk and develops a bitter taste. The soil itself should be well-draining, loose, and rich in organic matter to support the rapid growth of the leaves. Romaine prefers a slightly acidic to neutral soil pH, ideally ranging from 6.0 to 7.0 for optimal nutrient uptake.
Step-by-Step Seed Sowing Techniques
Gardeners have the option to either direct-sow Romaine seeds outdoors or start them indoors for an earlier yield. Starting seeds indoors in small cell trays approximately four to six weeks before the last frost date gives plants a head start, particularly in colder climates. However, direct sowing eliminates the need for transplanting, which can sometimes shock the young plants.
Regardless of the method chosen, Romaine seeds require light to germinate, so they must be planted very shallowly. The seeds should be barely covered with soil, at a depth of no more than one-quarter inch. For direct sowing, plant seeds about one inch apart and plan to thin them later, or sow two to three seeds every 9 to 12 inches where you want the final plants to grow. Rows should be spaced 12 to 18 inches apart to allow room for the tall heads to develop and for proper air circulation.
After sowing, the area must be watered gently with a fine mist to avoid washing the shallow seeds away or burying them deeper. It is important to keep the top layer of soil consistently moist until germination occurs, which usually takes between seven and ten days.
Nurturing Seedlings Through Early Growth
Once the seedlings emerge, consistent moisture management is paramount, as dry soil can quickly stunt their growth. The goal is to keep the soil evenly moist but never waterlogged, which can lead to root rot or fungal issues. Watering at the base of the plants, rather than overhead, helps prevent diseases like downy mildew that thrive on wet foliage.
If the seeds were direct-sown closely, thinning is a necessary step once the seedlings have developed two to three true leaves. This process involves removing the weaker or excess seedlings to ensure the remaining plants have sufficient room to mature into full heads. Final spacing should leave about 8 to 12 inches between each plant, depending on the specific variety, and the removed seedlings can often be eaten as microgreens.
Seedlings started indoors need to be gradually acclimated to outdoor conditions before transplanting, a process known as hardening off. This transition takes about seven to ten days and involves slowly introducing the plants to direct sunlight, wind, and fluctuating temperatures. Begin by placing the trays outside in a shaded, protected location for a few hours each day, progressively increasing the duration and exposure to morning sun over the course of the week. This preparation toughens the plant cell walls and minimizes transplant shock when the young Romaine is finally moved into the garden bed.