Lettuce is a cool-season crop that thrives in moderate temperatures. The time required to grow a harvestable head ranges from one to three months, depending on the variety and environmental conditions. Achieving a dense, fully-formed head requires more time and careful management than harvesting loose leaves.
Timelines by Lettuce Variety
The duration required to grow lettuce is primarily determined by its genetic type, which dictates its growth habit. Lettuce is categorized into loose-leaf and heading varieties. Loose-leaf types, such as Black Seeded Simpson or Salad Bowl, are the fastest to mature. These can be harvested as baby greens in 30 to 45 days, or reach full size in about 50 to 60 days.
Butterhead or Bibb varieties form a soft, loosely-packed head and represent a middle ground in maturity time. Varieties like ‘Buttercrunch’ typically require approximately 55 to 70 days to form their characteristic tender, cup-shaped heads. This type offers a balance between the speed of loose-leaf lettuce and the denser structure of more compact types.
The varieties that require the longest time to mature are Romaine and Crisphead. Romaine, known for its upright, elongated leaves, takes between 60 to 80 days for a full harvest. Crisphead, or Iceberg lettuce, forms the tightest and firmest head, often needing 65 to over 90 days to reach a fully dense, harvestable state.
Starting Methods and Time Savings
Planting seeds directly into the garden (direct seeding) is the simplest approach but adds time to the maturity timeline. Direct seeding requires accounting for the germination period, which can take 4 to 15 days depending on soil temperature. These plants also spend their slowest initial growth period exposed to unpredictable outdoor conditions.
A more time-efficient method is to use transplants, or “starts,” which are seedlings grown indoors under controlled conditions. Starting seeds indoors approximately three to four weeks before the intended outdoor planting date bypasses the slow and risky germination phase in the garden. This strategy can shave up to two to three weeks off the total time required for a mature head. By the time the small plants are moved outdoors, they have already developed their first true leaves and are structurally stronger, allowing them to establish themselves and grow quickly in the garden bed.
Environmental Factors Affecting Growth Rate
Lettuce is sensitive to temperature, performing best when air temperatures are consistently in the 60°F to 70°F range. Cooler temperatures, particularly those below 45°F, will dramatically slow the plant’s growth, extending the time to maturity.
The most significant threat to a predictable timeline is high temperature, especially when it rises above 75°F. This heat can cause the lettuce plant to prematurely initiate bolting, which is the process of sending up a tall flower stalk to produce seeds. Bolting effectively ends the harvest window because it causes the leaves to develop a bitter taste and shifts the plant’s energy away from leaf production.
Adequate light and consistent moisture are also necessary to maintain a rapid growth rate. Lettuce requires plenty of light for robust, quick growth, and insufficient light will result in leggy, slow-maturing plants. Furthermore, because lettuce is primarily water, consistent soil moisture and a steady supply of nitrogen are needed to fuel the continuous production of fresh, crisp leaves.
Harvesting for Full Heads Versus Continuous Yield
Harvesting a full head of lettuce aligns with the longest maturity times and concludes the plant’s growth cycle. For heading types like Romaine or Crisphead, the plant is ready once the center feels firm and dense when gently squeezed. Harvesting involves cutting the plant at the base, which removes the entire plant and ends its production.
In contrast, the strategy of continuous yield, often called “cut-and-come-again,” involves partial harvests typically used with loose-leaf varieties. Outer leaves are snipped off, or the entire plant is cut about an inch above the crown, allowing the central growing point to remain intact. This enables the plant to quickly generate new leaves, often within two weeks. While this provides a quicker, ongoing supply of greens, it never results in a compact, fully-formed head. Head lettuce is grown specifically for the single, dense harvest and is stored best by keeping it cold (35°F to 40°F) immediately after cutting.