Bolting is when a vegetable or herb goes to seed before it’s mature. Lettuce, brassicas and herbs such as parsley, basil and cilantro are all prone to bolting. If these plants are stressed, stalks will shoot up from the center of the plant producing flowers and seeds. Plant stress can come in many forms; temperatures over 85o F, long periods of high light intensities, drought, unfavorable growing conditions, and overcrowding all contribute to bolting.
Although the leaves are still edible, bolting causes them to taste very bitter. Once a plant has begun to bolt, there is no way to stop it and the plant should be pulled out and composted.
There are many ways to prevent bolting:
- Begin lettuce and brassica crops inside with lights and plant seedlings in the spring when conditions are still cool.
- Water plants deeply when there is less than an inch of rain each week.
- Use companion planting methods such as growing lettuce with tomatoes. Your crops will grow in full sun when the tomato seedlings are small. As the temperatures heat up they will be shaded by the large tomato plants.
- Plant seedlings under row covers, such as Reemay, or high tunnels (these covers heat up the soil beneath) to extend the growing season in early spring and into the fall.
- When temperatures heat up, cover plants with shade cloth (this fabric is dark and casts a shadow, cooling plants below).
- Practice the harvest method known as “cut and come again.” Harvest outer leaves of lettuce and kale and allow the plants to keep producing. This method can also be used with herbs such as basil and cilantro.
- Plant succession crops of lettuce and herbs to extend the harvesting season.
- Plant bolt resistant varieties of lettuce and brassicas.