Bolting refers to the tendency of some plants to encounter a kind of “growth spurt” in order to produce seeds. Certain kinds of plants—such as lettuce, kale, cilantro, parsley, spinach, broccoli, onion, and celery—can produce quick-growing flowering stems due to age or environmental conditions.
The problem with this for the gardener is that once this process of bolting has begun, the plant will stop putting energy into producing the edible parts (like the roots and leaves) of the plant and focus instead on creating flowers and seed. This means that the taste and quality of the edible parts of the plant will change and decrease. Because of this, gardeners try to prevent plants from bolting if possible. Cutting back plants when they start to flower can help with bolting. Some herbs will put more energy into producing leaves and will put off bolting if you harvest frequently. You can also find slow-bolt plant varieties.
A plant may bolt for a number of reasons. It can occur simply because the plant has reached a certain point in its life cycle. It can also happen because of stress caused by hot conditions, lack of water, or poor soil conditions.
When the growing season comes to an end, you can allow plants to bolt and reseed for the next year if you like. Just don’t disturb the soil around these plants and you may find a new crop show up in the spring.