If you’ve ever planted a crop of lettuce with hopes of a leafy green harvest only to find a bouquet of flowers before the greens were ready, you are familiar with what gardeners refer to as “bolting.” This is undesirable for the gardener because it interrupts and typically ends the vegetative growth. There are ways to delay and even prevent bolting by providing desirable growing conditions.
Outside the garden, bolting is related to running away fast. This image symbolizes what a plant looks like as it bolts. Bolting is a plant’s response to the growing conditions and, with annuals, it’s a sign that the end of life is coming soon for that plant. Though a plant isn’t going to physically run away when it bolts, it does rapidly grow away from the vegetative stage to flowers and seeds.
It is easy to identify when a plant is bolting because it will send up a taller stalk that is often woodier than the rest of the plant. This growth will happen quickly and will likely only have a few leaves. The stalk will develop flowers and the vegetative growth will slow or even stop altogether because the plant’s energy shifts to seed production. Plants such as broccoli and cauliflower will show yellow flowers opening on developing heads. Younger plants may grow tall and flower and never produce an edible head.
Cool season vegetables, including turnips, spinach, radishes and cauliflower among others, are subject to bolting as the temperature rises and day length increases. As we get into our summer heat you will notice the cool season vegetables finishing their life cycle and promoting the growth of future plants by developing flowers and setting seeds. Bolting is premature flower development, which can happen if spring crops are started too late and don’t reach maturity before the summer heat.
Other environmental factors can promote bolting as well. Plants that are under drought stress may respond by sending up flowers to ensure seeds will be produced before the plant dies. If the roots are restricted, the plant may bolt as well. Limiting the amount of stress on your plants is a good gardening practice that not only prevents disease, but also prevents premature bolting.
Once a plant has bolted the harvest is usually over. Leaves on bolted plants will be bitter and unpleasant. To prevent bolting keep the roots stress-free. Keep a layer of mulch over the soil to cool plant roots. Ensure the garden is receiving sufficient water to prevent drought stress. Root stress caused by transplanting can also encourage bolting so if you are a container gardener be sure to choose the right container for your plants to mature into. Direct seed crops that are sensitive to transplant-shock such as carrots and other root vegetables. Follow the recommended planting date for your zone to avoid planting too late in the spring or early in the fall. Reduce sun exposure by adding a shade structure over your sensitive crops as the day-length increases.
If your efforts to delay bolting are unsuccessful, you may decide to gather the seeds that develop for next year’s garden. While it may be disappointing to see the harvest end so soon, it is amazing to understand the processes in the garden. Each plant is in tune with the environment around them. This interconnected relationship allows the plant to respond in a manner that ensures future generations of plants.
Cynthia Domenghini is an instructor and coordinator for K-State’s horticultural therapy online certificate program.