Saving Seeds from Biennial Crops

Some crops, including many beloved vegetable varieties, are biennial. That means that they spend the first year of their life focusing on vegetative growth and reproduction in the second year. In other words, saving seeds from such crops requires growing them for one season, then storing or protecting them over the winter, then replanting next spring and letting them go to seed.

Although these extra steps sometimes deter beginning seed savers from attempting to save seeds from biennials, seeds saved in the same place where they will be grown tend to be stronger and more robust than seeds from elsewhere. That’s especially true for biennials, which have two growing seasons to acclimate to their local environment, enabling the seed saver to then select seeds from the plants that fared best. So, it just might worth the effort!

Common biennial crops are composed of some members of four plant families: Alliaceae , Amaranthaceae, Apiaceae, and Brassicacae. These include carrots, parsnips, celery, celeriac, parsley, beets, chard, kale, kohlrabi, Brussels sprouts, some broccoli, turnips, rutabaga, onions, and leeks. Below are a few essential steps to keep in mind when overwintering biennial seed crops. The seeds themselves will need to be dry-processed. To learn more about how to do this, take a look at our article on Harvesting, Cleaning, and Storing Dry-Seeded Crops.

Selection: Biennial roots are a great opportunity to do selection work: for storeabilty, shape, color and even taste. Since there is no chance of crossing in year one, anyone cold store any biennial from their garden right now for next year! Only save seeds from plants that are healthy and express desirable traits. Small and younger plants overwinter better than older ones, so plan on saving more crops from your fall garden than your spring plantings. Kale and other brassicas that are planted out in the field as seedlings in August are better for overwintering than brassicas that have been growing since May. Crops that grow slower, like Brussels sprouts or celeriac can be planted in July for seed saving purposes. Alliums like leeks and onions need the most time and should be planted in spring.

Remember to consider your seed population. Although one kale will produce more than enough seeds to use in a home garden, it’s best to save more than one plant in order to increase that variety’s gene pool. Seeds from six kales, for example, will have the chance to inherit more positive traits than seeds saved from just one.

Protection or Storage: In a northern climate, most biennials need to be dug up and stored during the coldest months. The hardiest ones such as parsnips or leeks can remain in the ground but even they require some protection from harsh weather. Either way, wait until a few light frosts pass by, as this will help trigger dormancy in the plants.

If digging out your biennials, don’t wait too long until the ground is frozen solid and digging will be nearly impossible! A few consecutive nights with temperatures below freezing is a good time to begin digging. Dig carefully, trying not to damage the roots (as that will speed up decay). Cut off remaining leaves (always above the crown) and brush off excess soil, but do not wash. The roots can then be buried in moist, but not wet (to prevent mold growth) media such as sand, shredded leaves, or sawdust. Biennials have to be stored in a cold environment to undergo vernalization (a cold period, to imitate winter, in this case - a mild one), in order to produce a good seed crop, for 6 weeks. The winter storage environment needs to be moist and cold, but not freezing - ideally ranging from 35 to 38 degrees. Obviously, this can't always be achieved perfectly and the plants are generally forgiving. A root cellar is perfect, but a fridge works fine for this too. A homemade cellar can be made by digging a hole below the freeze line and burying a storage container (bucket, old freezer, etc) in it.

Hardier varieties like parsnips and leeks can overwinter right in the ground. They experience vernalization naturally. Tucking them in for winter with mulch or straw and putting a row cover over them will help them survive the coldest periods. And, snow will actually help insulate them.

Replanting: In late spring, after chance of frost has passed, pick the best specimens from your stored collection and replant them as you would mature plants. Plant root crops as deep as the leaf crown, no deeper. Greens and fruiting plants can be planted in as far as their root reaches. For particularly tight cabbage heads, cut an X into the top of the head to make sure the cabbage flower stalk can grow out of the head.

Look out for our post on winter storage tips next week. We'll discuss temperatures, medium, and prep in more detail.