Head lettuce, including varieties like crisphead, butterhead, and romaine, differs from loose-leaf types by forming a compact, dense structure of leaves. This cool-season crop requires specific conditions and consistent attention throughout its relatively short growing cycle. Successfully growing the plant from seed to a fully formed head involves careful preparation and strategic timing of planting and maintenance.
Environmental Requirements and Soil Preparation
Head lettuce thrives as a cool-season annual, preferring average temperatures between 60°F and 65°F. While it tolerates full sun, partial afternoon shade is beneficial in warmer climates to prevent premature bolting or bitterness. The soil must be rich in organic matter and reliably well-draining, as the shallow root system suffers in saturated conditions.
Preparing the bed involves incorporating aged compost or manure deeply into the soil before planting to establish a nutrient-rich foundation. Head lettuce performs best in a soil pH range of 6.0 to 6.8, which is slightly acidic to nearly neutral. A soil test can confirm the existing pH, allowing for amendments like lime or sulfur to bring the environment into the preferred range before any seeds or transplants are introduced.
Sowing and Transplanting Head Lettuce
The planting calendar for head lettuce typically centers around early spring, as soon as the soil can be worked, or late summer for a fall harvest. Seeds can be started indoors in trays three to four weeks before the last expected frost, allowing for a jump-start on the season. Temperatures for germination are best kept below 70°F, as warmer conditions can induce thermal dormancy in the seed.
When sowing directly into the garden, place seeds about one-quarter to one-half inch deep, covering them lightly with fine soil. If using transplants, the young plants must be hardened off for three to seven days by gradually exposing them to outdoor conditions before final planting. To ensure proper head formation, space crisphead or butterhead varieties approximately ten to twelve inches apart. This spacing prevents crowding and allows for adequate air circulation.
Essential Care During Growth
Consistent moisture is paramount for head lettuce, as its shallow roots cannot tolerate dry soil, and fluctuations can lead to off-flavors or tip-burn. The plants require about one to two inches of water per week, delivered through shallow, frequent irrigation to keep the root zone evenly moist. Utilizing a drip system or careful hand-watering helps ensure that water penetrates the soil without wetting the foliage excessively, which can encourage fungal issues.
If seeds were direct-sown, the young plants must be thinned to their final ten to twelve-inch spacing once they have developed three or four true leaves. Removing the smaller seedlings directs nutrients toward the remaining plants, promoting large, firm heads. Head lettuce is a heavy feeder, especially of nitrogen, and benefits from a side-dressing of a nitrogen-rich fertilizer about four weeks after transplanting. This nutrient boost supports the rapid vegetative growth that occurs just before the head fully forms.
Recognizing Maturity and Harvesting
Determining the right time to harvest a head of lettuce is based on two primary factors: size and firmness. The head is ready when it has reached the typical size for the specific variety and, most importantly, feels solid and dense when gently squeezed. Waiting too long, especially as temperatures rise, can cause the plant to bolt, sending up a flower stalk and turning the leaves bitter.
The best time of day to harvest is in the early morning, as the leaves are at their crispest and most hydrated from the cool night air. To harvest the full head, use a sharp, clean knife to make a single cut at the base of the plant, just above the soil line. Tight-heading varieties are typically harvested all at once.