How to Save Seeds from Biennial Plants

Take your seed-saving know-how to the next level by learning how to keep seeds from open-pollinated biennials, including beets and Swiss chard.

| Summer 2017

  • Beets and Swiss chard are forms of the same species, Beta vulgaris. If different varieties of these plants are in flower at the same time, they can easily cross-pollinate and produce seeds that will not be true to type.
    Photo by iStock/sorendls
  • To save seeds from Swiss chard, dig it up, trim the leaves to about 3 inches in length, and then replant in containers with slightly moist potting mix or sand before placing them in cold storage.
    Photo by iStock/brandtbolding
  • Younger plants, provided they’re of reproductive size (typically having eight or more true leaves), are less susceptible to winter cold and are often set out late in the season to overwinter.
    Photo by iStock/FatCamera
  • Mature beet plants may reach four to five feet in height and take up a significant amount of space.
    Photo courtesy Seed Savers Exchange
  • Beets can be replanted in spring to flower and go to seed.
    Photo courtesy Seed Savers Exchange
  • Beets can be dug up, stored with their tops cut short, and then replanted in spring to flower and go to seed.
    Photo courtesy Seed Savers Exchange
  • Rainbow chard is coveted for its brightly colored stalks. Each color is in fact its own cultivar and must be isolated from the others when flowering to pass its color on to the next generation.
    Photo by iStock/dancingfishes
  • The small, relatively inconspicuous flowers of Swiss chard and beets are typically pollinated by wind, which is why they require an isolation distance of 800 feet or more from other flowering varieties of B. vulgaris. Given the biennial nature of this species, this isn’t hard to manage.
    Photo courtesy Seed Savers Exchange
  • One of the most common mistakes for novice seed savers is to not allow the seed to mature thoroughly before harvesting. Although seeds may continue to dry and harden, seeds don't really continue to mature after the seed heads have been cut from the plants. B. vulgaris seeds should have turned from green to tannish-brown before being collected. The spikes mature sequentially from the base of the flower stalks upward.
    Photo courtesy Seed Savers Exchange
  • Those who grow broccoli and cauliflower without saving the seeds will still benefit from understanding vernalization. For these plants to produce their flower heads (which are what we eat in immature form), they need to be exposed to a certain amount of cool weather to induce flowering. Most of these crops typically need 1 to 4 weeks of cumulative temperatures below 50 degrees after they’ve reached sexual maturity.
    Photo by Adobe Stock/mushy

We save seeds for many reasons: tradition; the idea of seed sovereignty and not being beholden to seed companies; and ensuring that our favorite cultivars don’t disappear. The most obvious reason for seed saving is that we want more plants. And when it comes to saving our favorite vegetable seeds, more plants mean more food. But some vegetables are easier to bring to seed than others. Self-pollinating annuals, such as lettuce and beans, are the easiest from which to save seed. These are followed by other annual crops, such as tomatoes, pumpkins, or peppers, which may require some level of isolation or pollination management, but other than that are grown similarly to how they’re grown for eating.

Biennial crops (varieties that flower, bear fruit, and set seed in their second season before reaching the end of their life-cycle, such as beets, chard, and many brassicas) are more challenging to grow for seed and require a deeper understanding of botany and the processes that bring plants to seed in the first place. Additionally, biennials grown for seed are brought to a state that we aren’t as familiar with, because we typically harvest these plants in their first year.

Download a custom seed packet template for storing your beet seeds.

Basic Seed Saving

Some principles of seed saving are universal, no matter which crops are being grown for seed. Seeds are the product of the fertilization of a plant’s flowers, which brings about fruit and seed production. Seeds that are true to type (seeds that bear the traits of their parent) can only be saved from open-pollinated cultivars that are isolated from cross-pollination with other varieties within their species. This can be confusing because some species contain more than one crop type, and the flowers of these plants can cross with one another if they’re in bloom at the same time. Cabbages, collards, cauliflower, European kales, kohlrabi, broccoli, and Brussels sprouts are all members of the same species, Brassica oleracea. Beets and Swiss chard are also forms of the same species, Beta vulgaris. If different varieties of these plants are in flower at the same time, they can easily cross-pollinate and produce seeds that will not be true to type, or characteristic of their variety. Additionally, some of these crops are self-incompatible, meaning that the pollen from a separate, genetically distinct plant of the same variety must fertilize its flowers to produce true-to-type seeds. In this case, more than one plant has to be grown, although growing a larger population of plants is always a good thing because it helps to maintain genetic diversity.



The cole crops of B. oleracea have an added complication in that some of the crop types within the genus are annual and flower in their first season, while others are biennial and flower after overwintering. If growing these for seed, you’ll need to make sure only one variety within the species is in flower at a time to prevent cross-fertilization. Whatever the crop, in order to flower and bear seed, biennial plants must reach a certain size (reproductive growth is typically possible after plants have eight or more true leaves) and then be exposed to a certain amount of cold for a period of time to trigger flowering and subsequent fertilization. This cold treatment is known as “vernalization” and is critical in bringing biennial crops to seed. The difficulty of this process is that the proper vernalization temperatures need to occur for a cumulative (non-consecutive) length of time without temperatures getting so cold that they damage the crop. In some areas, this is done by creating the necessary conditions in a managed way — by digging plants, potting them up, and storing them in a cold cellar or garage; or by digging roots of some crops, such as carrots and beets, and storing them in a refrigerator so they’re exposed to the cold they need without being damaged by temperatures that dip low enough to damage the plants. In some regions of the country, these conditions occur naturally while the plants are still in the ground, making the whole process much easier to manage.

It’s important to remember that these plants need to reach a minimum size and maturity before vernalization so they’re able to set seed in the second season, and this usually involves having eight or more leaves in the first season or a stem that’s about 1/2-inch in diameter. Surprisingly, younger plants are often better adapted to surviving winter than larger plants, so seed savers will often direct sow or set them out in summer to attain the ideal size before the plants are ready to be overwintered.






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