Romaine lettuce, also known as Cos lettuce, is a popular variety recognized for its tall, crisp leaves and robust, slightly sweet flavor. The time required to grow Romaine from seed to a fully mature head typically falls within a broad window of 60 to 90 days. The actual duration depends on whether the goal is a small harvest of baby greens or a fully developed, tightly bunched head of lettuce.
The Romaine Growth Timeline Seed to Maturity
The journey of a Romaine plant begins with the seed, which usually germinates within 7 to 14 days under ideal moisture and temperature conditions. Following germination, the plant enters the seedling stage, developing its first true leaves over the next three to four weeks. During this time, it is important to thin the plants to ensure adequate space for development.
Growth accelerates into the vegetative stage, and the first harvest of leaves can be taken early. The plant is ready for a “baby leaf” harvest when the leaves are about four to six inches tall, typically 30 to 40 days after the seed was sown. This early harvest allows the plant to continue growing while providing produce sooner.
For a full, mature head, the plant requires more time, reaching full size generally between 65 and 70 days after planting the seed. Starting with transplants, which are small plants already past the germination stage, can shave several weeks off this total time. Transplants offer a quicker path to a harvestable size and a more predictable maturity date.
Environmental Factors Influencing Growth Rate
The speed at which Romaine progresses through its growth stages is highly sensitive to environmental conditions. Romaine is a cool-weather crop, and optimal growth occurs when temperatures are consistently in the range of 60 to 70 degrees Fahrenheit. Maintaining temperatures within this band encourages rapid leaf expansion and the development of a sweet flavor.
Temperatures above 80 degrees Fahrenheit are the primary cause of bolting, which drastically shortens the harvest window. Bolting is the plant’s premature response to heat stress, causing it to shoot up a central stalk to produce flowers and seeds. This change also causes the leaves to develop a bitter taste and a milky white substance, effectively ending the period for a quality harvest.
Full sunlight, meaning at least six hours of direct light daily, is necessary for fast growth and the formation of a dense head. In regions with intense summer heat, providing partial shade during the hottest afternoon hours can help regulate the plant’s temperature and delay bolting. Consistent moisture is equally important, as dry soil can trigger bolting and bitterness in the same way high heat does.
The type of Romaine variety selected also influences the time to maturity, with some varieties naturally maturing a few days faster than others. Varieties may have a Days to Maturity (DTM) listed on the seed packet that can vary by five to ten days. Providing a rich, well-draining soil with ample organic matter ensures the plant receives the steady nutrients it needs to complete its life cycle efficiently.
Harvesting Methods and Timing for Romaine
A mature Romaine head is ready for harvest when it feels firm, its leaves are a deep green color, and the head has reached a height between six and twelve inches, depending on the variety. Checking the head’s firmness is a reliable indicator, as an immature head will feel loose and easily compressed. Harvesting should be done in the morning before the sun’s intensity causes the leaves to lose moisture and crispness.
One common technique is the cut-and-come-again method, which involves removing only the outer, mature leaves from the plant. This allows the smaller, inner leaves to continue growing, effectively extending the harvest period for several weeks from a single plant. The central growing point must remain undamaged for this continuous production to occur.
For a full head harvest, the entire plant is cut off at the base, typically about one inch above the soil line, using a sharp, clean knife. Leaving a small portion of the stem and the roots intact often allows the plant to produce a second, smaller flush of leaves. While this regrowth will not form a dense head like the first, it provides an additional harvest before the plant’s growing cycle concludes.