Let Biennials Bloom: How to Save Seeds for Next Year

Keeping cabbage, carrots, and collards in the garden for their second year of growth will gift you with more seeds than you need for the next growing season.

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by Adobestock/Daniel Vincek

Biennial plant definition: plants that need two growing seasons to create seeds. Learn how to save seeds for next year by cultivating your biennial plants.

If I’ve read it once, I’ve read it a dozen times: “Saving biennial seeds is a challenge.” It seems many of my gardening books take the position that it’s too hard for the novice and that we’d be better off buying more seed packets every year instead.

Well, this novice gardener is a bit stubborn, and that advice didn’t line up with my desire for self-sufficiency. So, with total inexperience, an armload of gardening books, and a handful of heirloom seeds, I decided to try anyway. A few years later, I’ve grown a lot of plants, made a big mess, and — both because of and despite my bumbling efforts — ended up with the wonderful gift of jars upon jars of heirloom seeds to fill my gardens in the future.

Those books were right; it was a challenge. But was it worth attempting? Absolutely! If you want to see whether you, too, can join the ranks of heirloom biennial seed savers, here are some mistakes I made and things I learned along the way. If I can figure this out, so can you!

Biennial Plant Definition

Biennials — plants that need two growing seasons to complete their life cycles — live interrupted lives, as far as the backyard gardener is concerned. Many of us may have forgotten the true nature of those beets, carrots, and turnip bulbs. To us, they’re food. But to the plants, they’re hope for spring proliferation. In such favorable conditions as a well-tended garden with regular watering and weeding, biennials can produce massive bulbs or tubers. That storage organ will sustain a biennial through the cold winter, giving it a head start once spring thaws allow it to complete the seed-bearing chapter of its life — that is, until the gardener pulls it and roasts it with butter and caraway seeds.

Closeup of a yellowed parsnip seed head.

The seed-saving gardener, therefore, must choose the best of the best and then let those biennials transcend the casserole dish. One way or another, we have to keep those plants alive so they can carry on their life cycles next spring and, of course, make seeds.

For gardeners in milder climates, that may mean spreading a thick blanket of mulch to keep the worst of winter from killing off your selected plants. For those in colder climates, cold frames or root cellars will be necessary to prevent frozen demise. Then, in early spring, either pull back the mulch to let the roots see the sun of a new season or replant them carefully so they can wake up back in the earth they so love. (Detailing the nuances of this winter wait is beyond the scope of this article, so I recommend reading the best book I know on the subject, Mike and Nancy Bubel’s Root Cellaring.)

Managing Biennials in Your Garden Rotation

Every garden plant has an idealized form. Usually, it’s represented by the image displayed on the seed packet: beautifully proportioned agricultural perfection. Seed-bearing plants, on the other hand, are anything but. The world is full of bizarre whimsy when you allow plants to shoot up their seed stalks. Cabbages will break open like eggs, and from their centers will emerge giant stalks bedecked with surprisingly lovely yellow blooms. Swiss chard will look like a caffeinated 5-year-old drew it, with far-reaching, nubbin-covered branches that don’t seem to know where they want to grow and opted for everywhere. Carrots will sprawl, their heavy heads contemplating the ground.

Closeup tangle of green kale seed pods.

All this to say, biennials in their second year will take up a lot of space, more than they did in their first year. All that energy stored in their roots will funnel into incredible amounts of growth. That growth can really get in the way if you didn’t plan for it.

That was my error with my parsnip placement this past year. Once spring hit, the parsnip plants shot up well over my head, lush with foliage. That was when I realized I’d placed them on the southern border of the garden. They now cast a huge shadow over the rest of the garden, and the lettuces I had unthinkingly placed behind them barely had a chance to grow in the unexpected shade.

Clump of growing green parsnip plants in a garden.

Other plants may not grow as tall as parsnips, but they will grow large, sometimes somewhat awkwardly. They’ll take up a lot of space and won’t give you anything for the salad bowl in the meantime. Don’t expect your garden to look like a postcard as you try to stake a mess of spindly Swiss chard seed stalks in an orderly fashion or tie together the carrot stalks to try to make them remember they once were planted in a row. If you can, embrace the chaos with the hope of future seeds, and try not to think of the garden space as being “wasted.”

Keep Your Species Straight

Once your plants have made it through winter and sent up their seed stalks, they’ll get their flowers gussied up to meet and mingle. Your job as a seed saver is to make sure they pollinate with the right crowd. Sometimes, that’s easier said than done!

The first order of business is to know what species your plants are. Technically, kale, cabbage, collard, kohlrabi, and Brussels sprouts are all different varieties within the same species (Brassica oleracea), and that means they can all hybridize. The same goes for beets and Swiss chard, and likewise for carrots and the wild Queen Anne’s lace that’s filling a nearby field. For those just learning these complicated family relations and how to keep them separate, Suzanne Ashworth’s excellent book Seed to Seed is the best resource I can recommend.

Closeup of a carrot blossom about to bloom.

Once you know what you’re dealing with, the second order of business is knowing how your selected plants will get pollinated. Those that are insect-pollinated, for example, may need to be isolated to ensure purity. In my garden, even though I only grow one cultivar of carrot a year, I cover each handful of blooms with a mesh bag supported by a stake. This protects my seeds from being mixed with the Queen Anne’s lace that surrounds my land. It also means I need to take the bags off every day and hand-pollinate each flower to ensure fertilization. With carrots, that’s as simple as patting one flower with my hand to get it covered with pollen and then patting a different flower with the same hand.

I try a different approach with my insect-pollinated cabbage-family plants. Since cabbage’s wild ancestor (B. oleracea) is native to western and southern Europe, I don’t have to worry about my cabbage cultivars mixing with a wild plant. Instead, I can focus on making sure they don’t mix with each other. In my garden, I choose two different cultivars to save every year, covering them on alternate days to keep them from hybridizing. Half the days, the cabbage blossoms are covered, and the other half of the days, the kale is covered. The bees take care of the rest!

Five bagged carrot blossoms

Those plants that are wind-pollinated, such as beets and Swiss chard, are a bit more out of your control. My advice is to plant as many beet or Swiss chard cultivars as you want every year, but only plan on saving a single cultivar of the lot for overwintering. If you choose to save a cultivar of beet seed one year, you can plan on saving Swiss chard the next year. Unless first-year plants get stressed and bolt, you’ll be able to save pure seed from your selected cultivar every year. You’ll get plenty of seeds each attempt — more than enough to cover the “gap” years — and you’ll save yourself a headache in the meantime.

How to Save Seeds for Next Year

So, your roots have survived winter. They’ve sent up those flower stalks. They’ve flowered. You’ve kept them pure. They’ve made seed pods! And then? Well, then, they’ll take their sweet time to get those seeds finished.

It can feel like eons pass when waiting for seeds to mature. Parsley seeds I planted in the ground in April of 2017, for example, didn’t bear mature seeds until September of 2018! It’s important to let those seeds reach full maturity, however, or all your efforts will be a total waste. I admit I’ve impatiently pulled almost-dry seed pods off the plant so I could move it out of the way, only to have the seeds shrivel up into unfinished bits of disappointment. So, be patient. Typically, once seed pods are crunchy-dry and the seeds fall out freely, or once seeds crumble off the umbel at the touch of a finger, they’re finally ready.

Two jars of dried seeds and a packet of saved seeds on a wooden

As you’ll see, one of the amazing things about many of these biennial plants is that when they go to seed, they really, really go to seed. You’ll end up with far more seeds than you could probably plant in your garden — which is why seed sharing often becomes a natural byproduct of seed saving.

Once seeds are perfectly dry, clean and thresh them, and then place them in an envelope or jar. Be sure to label each one with the cultivar name and date of harvest. Do this immediately upon cleaning the seeds so nothing gets mixed up or mislabeled. Then, secure them in the freezer or in a cool, dry location, and breathe a sigh of satisfaction. Another pocket in your self-sufficiency tool belt has just been filled.

Grow Happy, Healthy Collards

  1. Use moist, fertile soil with good organic matter if you want to have young, tender leaves and keep your plants growing well, especially in warmer weather.
  2. Make sure the soil’s pH is slightly acidic. The soil pH in the Southeast, where collards were developed in the United States, is naturally 5.8 to 6.5, a bit on the acidic side.
  3. Plant collards in full sun. You can grow collards in partial shade, but they won’t grow as fast or produce new leaves for harvesting as often.
  4. Pay attention to spacing, and be sure to sow seeds in rows at least 3 feet apart. If you want bigger plants as you head into winter, leave enough space for them to grow. Young, tender greens are delicious, but making collard kraut is an option if the greens get too big.
  5. In most places that have a mild climate, you can plant collards twice — once in early spring and again in late summer for a fall or winter harvest. (In some cases, you can probably carry your spring collards through to fall.) Either direct seed them two weeks before your last frost, or, if transplanting, start your seeds indoors 4 to 6 weeks before your last frost.

Wren Everett and her husband quit their teaching jobs and moved their family to 12 acres in the Ozarks, where they’re establishing their dream of a self-sufficient, off-grid property.

  • Updated on Sep 6, 2022
  • Originally Published on Jul 27, 2022
Tagged with: biennial crops, gardening, seed saving, seedlings, Sow Hoe, Wren Everett
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