You walk into your vegetable garden and notice a tall, flowered stalk growing from the center of your lettuce (Lactuca sativa) or clusters of tighlty growing triangular-shaped leaves growing from the tops of your basil (Ocimum basilicum) and wonder what is going on. Your plants are most likely bolting, a common problem for vegetable gardeners, that will affect the taste and production of your plants. Knowing the causes and ways to prevent bolting will help you keep your garden from going to seed.
When a plant prematurely produces seeds and flowers, it's bolting. Typically, this is a problem for annual flowers and vegetables, such as lettuce and spinach (Spinacia oleracea), and biennials such as cabbage (Brassica pleracea), carrots (Daucus carota sativus), onions (Allium cepa), leeks (Allium porrum) and fennel (Foeniculum vulgare). It is also more common in cool-weather crops.
Bolting is brought on by stress. The most common cause is temperature stress. Extreme changes in weather, like high heat following a cooler spring or cold nights followed by hot days, will cause plants to bolt. Unseasonalby cold weather may also cause bolting. Drought, changes in daylight hours and intense sunlight can also make plants bolt.
When they bolt, your plants become undesirable for eating because leaves will become tough and the flavor will turn bitter. Bolting will also cause them to stop producing new leaves, instead investing their energy in growing flowers and seeds. If your lettuce and other leafy greens bolt, you can harvest the remaining leaves, but don't allow them to continue growing because new leaves won't be appetizing. If basil bolts, snip off the forming flower shoots as soon as you see them. This will perserve the flavor and texture of the leaves and cause the plant to produce new leaves.
You can prevent bolting by purchasing bolt-resistant cultivars from your local gardening store. Select smaller plants for your garden that have a stem thickness less than that of a pencil. These plants are less developed and less likely to bolt when weather turns warm. Keep plants indoors or in a greenhouse until weather is stable, and keep your plants watered to prevent drought stress. In hot climates, place plants under shade cloth to protect them from intense light and heat.
- Sunset Western Garden Book; Kathleen Brenzel-Norris
- Royal Horticultural Society: Bolting in Vegetables
- Oregon State University Extension Service: Plant Veggie Starts Early to Prevent Bolting
- Iowa State Univesity Extension and Outreach: Lettuce
- Sunset Western Garden Book of Edibles; Jim McCausland
- Hemera Technologies/AbleStock.com/Getty Images