Biennial vegetables are an excellent choice for gardeners who want to support beneficial insects, extend their growing season, and harvest seeds from their plants. Unlike annuals, which complete their lifecycle in one season, biennials grow in one season and bloom the next after a cold winter period. Many biennial vegetables also provide stunning flowers that attract a variety of beneficial insects.
Why Grow Biennials for Flowers and Seeds?
Last fall, I saw a large, overwintered garden carrot used as a dinner centerpiece. Although it was too mature to eat, it was a perfect example of what you can do with biennial vegetables: grow them not only for their edible parts but also for their flowers and seeds. Carrots, like many other biennial vegetables, bloom in late spring when nectar-rich plants are scarce—between the flowering of spring trees and shrubs and the arrival of summer annuals. This timing makes them vital for attracting pollinators and other beneficial insects. Over 300 species, including hoverflies and small wasps, are drawn to carrot flowers.
Biennial vegetables such as onions, celery, and parsley provide abundant seeds once they bloom. For instance, my overwintered beets produced so many seeds that the heavy seed spikes required multiple stakes to support them. The following year, I had hundreds of volunteer celery seedlings sprouting around my compost pile—an easy problem to manage.
Common Biennial Vegetables
Biennial vegetables are plants that require two growing seasons to complete their lifecycle. The first season is spent growing leaves, stems, and roots, while the second season is dedicated to flowering and seed production. Common biennial vegetables include beets, Brussels sprouts, cabbage, carrots, cauliflower, celery, chard, collards, kale, kohlrabi, leeks, onions, parsley, parsnip, rutabaga, salsify, and turnip.
Some of the hardiest biennials, like Brussels sprouts and kale, can survive the winter outdoors, while others, such as cabbage and carrots, benefit from winter storage as “stecklings”—roots or plant parts kept through winter and replanted in the spring.
How to Overwinter Biennial Vegetables
Successfully overwintering biennial vegetables ensures they can bloom in the spring. Here are a few techniques to help them through the colder months:
- Mulch: A deep layer of mulch helps protect vegetables like parsley and celery from freezing and thawing cycles, which can harm their roots. Once temperatures drop, adding a row cover tunnel can provide extra protection from ice, snow, and harsh winds.
- Storage in Buckets: For vegetables like cabbage, Brussels sprouts, and leeks, you can overwinter them by placing them in buckets filled with compost or damp, well-rotted sawdust. This creates a controlled environment that protects the roots. Make sure to trim off any leaves before storing the plants in a cold location, like an unheated garage, to minimize moisture loss.
- Refrigeration: Root crops like beets, carrots, and parsnips need cool, consistent temperatures to overwinter. Since most homes lack a traditional root cellar, your refrigerator can serve as an ideal storage space. Place healthy root vegetables in separate plastic bags, and store them at temperatures between 32°F and 45°F (0°C – 7°C). Commercial seed growers use this method because it preserves root quality and provides the necessary cold period for the plants to bloom and produce seeds come spring.
By employing these methods, you can grow biennial vegetables that not only provide food but also contribute to the ecosystem by attracting pollinators and producing abundant seeds. Overwintering these plants might take a little extra effort, but the results—beautiful flowers, buzzing insects, and a seed harvest—are well worth it.