Stretching stems are a sign that it's time to pick your leafy greens before they turn tough and bitter.
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The cool days of spring are ideal for growing delicious, nutritious lettuces, but when your plants start to bolt, it's time to make your final harvest. That's because lettuce grows fast in chilly, wet weather, yielding leaves that are succulent and tender, with a flavor that's usually brighter and better than the supermarket greens sold in bags. But when temperatures start to rise, lettuce plants begin flowering, or bolting. You'll notice the main stem starting to grow tall with lots of space between the leaves. Then, the leaves turn bitter and lose their juiciness. Here's what you need to know about bolting in lettuce so you can harvest your crop at its best.

drip irrigation system with lettuce
Credit: Helen Norman

Why Lettuce Bolts

Lettuce (Lactuca sativa) is an annual vegetable in USDA Hardiness Zones 8-10. Bolting in lettuce happens when the plant has matured and reached the end of its life cycle. This growth pattern also happens to many other cool-season plants, including cilantro, spinach, and broccoli. When a plant bolts, it's just doing what comes naturally. It produces flowers that form seeds, so more plants can grow, a process that's sometimes called "going to seed."

Bolting in lettuce is triggered by warm weather and the long days of summer, usually when the daytime temperatures climb above 75°F and nighttime temperatures are over 60°F. After bolting, lettuce leaves will taste bitter and grow slowly. The plant will use most of its energy to produce flowers, and then seeds before dying. You can't keep plants from bolting indefinitely, but there are a few ways to delay it, so you can keep harvesting tasty lettuce leaves.

Tips for Delaying Bolting

To ensure you can harvest your lettuce for as long as possible before it bolts, it's important to pick the best lettuce varieties and provide the right care for your plants. For starters, plant bolt-resistant or heat-tolerant types of lettuce, such as butterhead varieties or romaine cultivars like 'Sparx' and 'Salvius'. 

Start your lettuce outdoors early in the spring. It can tolerate a light frost and short cold snap, especially if it's covered for protection, so you can start picking young leaves before the temperatures increase. You can also plant lettuce in the fall in most regions and enjoy a late-season harvest until the plants succumb to a freeze. 

Lettuce thrives when the soil pH is between 6.2 and 6.8. If you don't know your pH, buy a test kit from a garden center, online seller, or nursery, or ask your local extension service to test your soil for you. Well-drained soil also helps lettuce grow better and faster, so mix in some organic materials, if needed. Adding nutrient to the soil will fuel healthy growth. Fertilize new lettuce plants with a 10-10-10 fertilizer.

Give your lettuce a break from full sun. Grow pots of lettuce on a porch or patio that gets some shade, plant it in the garden under taller plants, like corn, or use a shade cloth over your lettuce bed. Regular watering can also help delay bolting. Mulch around your plants with shredded leaves or clean straw to help hold the moisture in the soil.

When you harvest, take the outer leaves first and let the young, inner leaves keep growing. Cut or pull head lettuce before the heading plants get too old and big. Sow more lettuce seeds every few days or weeks. This won't delay bolting, but it will give you a continuous supply of leaves until it's too hot or cold to keep planting.

Benefits of Bolting in Lettuce

Although it means your supply of fresh leaves is coming to an end, bolting in lettuce isn't always a bad thing. The blooms on lettuce plants can attract pollinators such as bees and other bugs that prey on garden pests. You can also collect the ripened seeds of open-pollinated lettuces before they drop and replant them later. (Seeds saved from hybrid lettuces usually won't grow into the same kind of parent plant.)

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