How to Know When Romaine Lettuce Is Ready to Pick

Among the varieties of lettuce (Lactuca sativa), romaine, or cos, lettuce is ready to harvest when it's 70 to 75 days old. In your home garden, you can start adding the leaves to your salads and sandwiches long before that. It's perfectly OK to start harvesting leaves when they're smaller than full-size and the leaves are much more tender.

When your romaine lettuce is about 5 or 6 inches high, it's in the baby-leaf or mini-head stage, and you can start eating some of the crisp green leaves. Mini-head lettuce, by definition, is lettuce that is either not fully developed or is a cultivar that is genetically smaller. To avoid spreading plant diseases, wipe down your scissors or hand pruners with a solution of 1 part bleach to 3 parts water and allow the solution to dry. Choose leaves on the outside of the plant that are free of rot or wilt, cutting them about 1 inch from the plant stems. Harvest just a few outer leaves from each plant, which will allow the center leaves to continue to grow.

Your plants will be ready to harvest completely when the leaves are elongated and overlapping slightly, with a head that's about 6 to 8 inches high, suggests Clemson Cooperative Extension. That will be roughly 70 days -- but different varieties may vary on the timing. The 'Paris Island' variety, for example, is more long-standing, while 'Green Towers' is an earlier variety. Harvest the heads before the stems have grown overly large and when the ribs along the bottom-center of each romaine leaf are not overly large or milky-colored. A solid rib means the romaine is mature, but if the ribs are milky and tough, the lettuce will taste more bitter. Check your lettuce every day so you don't wait too long to harvest. Using your clean pruning tools, cut the head close to the leaf stem, about 1 inch from the soil line. You can also harvest the entire head when it's still immature and in the "baby" stage, suggests Michigan State University's Extension, to get that tender "baby green" taste.

Because romaine prefers cooler temperatures around 60 degrees Fahrenheit, you may be able to get a second harvest from the heads you've already harvested. If you cut your whole-head romaine about 1 inch from the soil line, it will start growing more leaves. As you did the first time around, harvest the outer leaves when the plant is about 5 inches tall, and then cut down the entire head when the leaves are 6 to 8 inches high and are slightly overlapping.

A few problems can make it difficult to get a decent lettuce harvest. If the tips of the leaves turn brown, simply trim off those edges with your clean scissors and then harvest the rest of the leaves -- or leave them to continue growing. This is typically caused by hydration issues, so be sure you're giving your lettuce frequent light watering.

Your romaine may also bolt and send out flower shoots, due to long, hot days. When this happens, cut down the entire plant, leaving 1 inch of stalk in an effort to grow a second harvest. Also try adding shade cloth to the area to keep it cooler. Lettuce that is allowed to bolt may taste more bitter, so harvest it as soon as you notice any sign of bolting. Wash the lettuce and store it in the refrigerator; after a few days the bitter taste may go away, suggests the University of Illinois Extension.