If this is your first experience with lettuce (Lactuca sativa), you’ll discover that your main problem will not be insects or diseases or even slugs (although the latter can be pretty horrific). Instead, bolting will be the main enemy.
Lettuce naturally grows rapidly when the days get longer and starts to bloom when it gets hot. When your lettuce begins to change from its original rosette shape to an upright stem bearing well-spaced smaller leaves, it is said to be “bolting”, that is, getting ready to bloom. Bolting occurs when a crop produces a flowering stem before it is harvested. That may not seem so bad, but the plant starts to divert its resources avay from the leaves (edible) to the flower stalk (inedible). Soon the leaves become bitter and are no longer worth harvesting. You can tell your lettuce plants are preparing to bolt when milky white sap flows from the base of leaves as you harvest them.
There are a few things you can do to delay bolting, most notably by keeping the soil around plants slightly moist at all times. (Drought tends to stimulate bolting.) For that reason, it’s always wise to mulch lettuce, as a good mulch will help tremendously to reduce evaporation and lower the soil temperature, keeping the soil moister. And sometimes Mother Nature lends a hand: when spring and early summer is cool and on the cloudy side, that will delay bolting. But eventually …
What to Do When Bolting Starts
Unless you intend to harvest lettuce seeds for next year’s garden – in which case you’ll want let one or two plants bolt and go to seed – it’s best to yank out the plants that are bolting and use the space to start more lettuce plants. In fact, for fresh lettuce all summer and even well into the fall, it’s wise to sow a few lettuce seeds every 2 or 3 weeks, thus ensuring you’ll always have a fresh supply of young plants.
Note too that some types of lettuce bolt earlier in the summer than others. That being the case, here is a blog about one type of lettuce that will last all season.
Can You Still Use Bitter Leaves?
If you catch your lettuce just as it is about to bolt (for example, when a plant or two have begun to produce an upright stem, but the others still form a rosette or when the flowering stem is still quite short), you can still harvest the leaves. Yes, they’ll be bitter if you try to eat them fresh, but there is a treatment you can try to reduce the bitterness. First rinse them in cold water, then dry them by gently patting with an absorbent cloth or by running them through a salad spinner. Now store them in the refrigerator in a ventilated container for 2 or 3 days. This should bring their original flavor back.