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Seed-Saving Biennialsby David Cavagnaro

I’ve been harvesting seed from all sorts of veg-etables since I was a kid growing up in northern California. In a benign climate such as we had there, getting a seed crop from your vegetables happens almost on its own. Leave a plant – lettuce, broccoli, Swiss chard, almost anything – in the ground just a little too long and pretty soon it’s going to seed. I never bought seed unless there was a new variety that I was after.

No matter where you live, it’s easy to save seed of annuals like tomatoes, peppers, lettuce, melons and squash. And in zone 8 and southward, biennial crops – the cabbage family, onions and most root crops – are easy too. But where winters are cold enough to freeze the ground hard, the biennials take a little more effort. A lot of people, even committed seed-savers, are unnecessarily afraid of trying.

Today I live in zone 4, where the winters get to 30 below. And I’m still saving seed from all sorts

of biennial crops from my home garden: cabbages, kale, Brussels sprouts, leeks, beets, chard, carrots, rutabagas, turnips. Once you understand the basic premise – you want to keep the plant in a dormant state, either indoors or in the garden, through the winter and then grow it on the following spring until it sets seed – the techniques aren’t diffi cult, they just take a bit more time.

Maintaining my family’s supply of biennial seed has become part of our routine for storing our winter vegetables. At harvest time we simply separate out some of the fi ner specimens as parent stock. We’re lucky to have a large root cellar, where the tempera-ture averages 32 to 40°F and the humidity about 90% – the cole and root crops keep very well. Early the following season we replant them outdoors, where they quickly go to seed. Since seed for most of these vegetables will keep fi ve or six years, I only need to do this for a handful of crops each year.

Brassica oleracea varietiesMany members of the family Brassicaceae are

annuals – mustards, Chinese cabbage, arugula, cress and others – but members of the species oleracea are biennials. Firm types of brassicas – kohlrabi, Brussels sprouts and the hard storage varieties of cabbage – are the easiest to save. The leafy brassicas (kale, collards and Savoy cabbage) tend to mold and rot. Broccoli and caulifl ower behave like annuals. I’ll talk fi rst about cabbage because the way I handle any other brassica is just a variation of the treatment I give cabbages.

I like to get my storage cabbages dug up and in pots in the root cellar before the temperature ap-proaches 20°F. I leave some cabbages in the garden later than that for eating (throwing blankets or other protection over them at night), but vegetables for the root cellar must be in excellent condition. Cold-dam-aged cabbages won’t last long before rotting.

Cabbages don’t have extensive roots. After removing outer leaves, leaving just the heads, I lift the plants with a shovel, shake off the dirt and place them in fi ve-gallon nursery containers, cramming about fi ve cabbages into each pot. I fi ll the contain-ers with soil or sand and water well. The heads stay absolutely perfect this way for seven or eight months. Sometimes the humidity causes the outer leaves to rot. I just pull those leaves off and there’s a perfect cabbage underneath.

Root Cellar with Biennials for Seed Saving(Photo by David Cavagnaro)

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With cabbages you can have your cake and eat it, too. All you need to plant out in the spring is the root with some stem – there are plenty of dormant buds along the stem that will sprout and go to seed. (Eat the seed cabbage heads last, though, because once the head is cut off, the stem is far more prone to rotting.) If you plant out a cabbage with the head still intact, cut an X in the top to make it easier for the fl ower stalk to emerge.

For loose-headed cabbages (early varieties. Sa-voys and collards), make a special planting for the seed crop, timed so you’ll have small plants with little heads when killing cold arrives. Dig the plants, strip all the leaves until only a head about the size of a ten-nis ball remains, and pot them up for storage like the others. A late summer planting of kale overwinters right in the garden under a layer of mulch if winter temperatures are not too severe.

One cabbage will give you plenty of seed. Every-thing in this family needs cross pollination by insects, however, so you’ll need at least two to get a crop and you must separate each cabbage variety from all other cabbages as well as any other brassicas. However, it takes far more than just two plants to maintain genetic viability in these biennial crops. Geneticists recommend a minimum of 20 plants of vegetables like onions, leeks, or brassicas. That may be more than most backyard gardeners have space for. If so, you can save seed for a generation or two (in other words, one or two times) before the genetic quality begins to slip, then buy in fresh seed.

In the home garden, it’s easier just to save seed from one brassica type each year and not worry about separation distance. The seed will last four years or more if kept dry at about 50°F. I routinely get fi ve or six years out of mine.

Russian kale is not a true kale; it is actually related to rutabaga, Brassica napus, and will therefore not cross with other kales or oleracea varieties.

Root cropsCarrots, beets, rutabagas, turnips and celery root

are not close relatives but are all brought through the winter in a similar way. In mild climates they can be left in the garden, perhaps with a little mulch to pro-tect from cold where freezes do not penetrate deeply. Where the ground freezes, it’s safest to dig them, trim the leaves and store them in sawdust.

Parsnips are the only root crop that can survive deep freezing. Even here in zone 4, I can leave them in the ground without mulching. The only danger is from voles, which can ruin root crops under mulch or snow.

I dig root crops for storage any time before the ground freezes, though it can be a hand-numbing job if the weather is very cold. I trim the leaves about a quarter inch above the root, brush off the dirt and layer the roots in wooden boxes.

Traditionally, sand is used to separate the lay-ers of root vegetables. But sand is heavy, so I prefer coarse sawdust or even the chipped leaves I use for mulch. Separate each root from its neighbor because some will inevitably rot (the separation keeps the decay from spreading through the whole box). Start with a fresh batch of packing material each season.

As with the cabbage family, select the best speci-mens for seed parents while you are sorting the crop for packing. Seed stock should go in separate boxes that are set aside, so there is no chance of eating them acci-dentally. Any roots with insects holes or other damage are most prone to decay and should be eaten fi rst.

All of these vegetables need cross-pollination so you’ll need to plant at least two of each to get seed. But keep in mind that many more, perhaps at least 20, are necessary to maintain long-term genetic integrity of these crops. Since these plants are much smaller than mature brassicas, a full patch does not take too much garden space.

Beets are wind pollinated and will cross with Swiss chard. The others are insect pollinated. Carrots will cross with the Queen Anne’s lace, but the gene for white roots is dominant, so any orange carrot you get the following season is sure to be true to variety type. Other root vegetables will cross within the group as well as with wild relatives.

Again, the easiest way to handle the problem is to grow just one from each group in a given year. Most of these seeds will keep four years or longer with little trouble. The exception is parsnip seed, which is notoriously short-lived. We like parsnips, and I renew the seed each year, which is as simple as leaving a few plants in the ground.

To cover any storage losses, I like to reserve six to a dozen of each root vegetable for the seed crop, but again, if you plan to maintain your seed stock through

Preparing Cabbages for Winter Storage(Photo by David Cavagnaro)

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several generations, up that number to about two dozen. All can be replanted outdoors as soon as the ground thaws in spring, set very close together in the row.

OnionsLeeks are one of the easiest biennials to save be-

cause: most are so very cold hardy. But regular onions are one of the more diffi cult vegetables – it’s hard to bring them through a long winter in a fully dormant state. Onion seed loses viability very quickly and you need to plant a good number of parents to keep the seed stock from gradually declining in quality. My family’s heirloom red onion kept getting smaller and smaller and producing more multiple-centered bulbs, until I learned to have 20 or more parents in my seed patch.

Let’s start with leeks. In moderate climates you can overwinter any leek outdoors with a bit of protec-tive mulch. Here I can only overwinter the hardiest varieties, which are generally the short, stocky ones. I dig them up and replant them in a trench at an angle, so the roots and growing tips are well protected with a bank of soil and only the tops of the leaves are above ground. Then I cover the leeks with a thick blanket of leaves. In spring, I just peel back the leaves and

let the plants go to seed. For most varieties and best insurance of success, I dig leeks in the fall and replant them densely, as many as I can fi t, if fi ve gallon plastic pots for root cellar storage.

I dig up my red onions in the fall and sort them for storage like the other crops, saving the very best 20 or so for the seed crop. In mild areas you could replant the best specimens immediately and protect with a light mulch of leaves or straw. In our climate where the ground freezes solid, onions tend to rot even if mulched, so we have to bring them indoors. They will keep in a cold room (32 to 45°F) at 60 to 70% humidity up to six months. They also keep well under very warm conditions – 77 to 95°F and about 65% humidity.

My onions sprout in late January or February. I pot them up so they can grow roots and move them into the root cellar. That tides them over until it’s safe to move them outdoors. Onion varieties will cross-pollinate with each other as well as with shallots and potato onions.

For seed to remain viable a long time it’s crucial that it be completely dry. Cut the partially dry plants bearing the seed crop and move them indoors to a very dry room. Harvest seed just as it’s ready to fall away from the parent plant or as the pods are about to split. If the seed still feels slightly damp, spread it on paper in a thin layer.

Store the seed in small paper envelopes labeled with the name of the plant, the variety and the date. The only truly airtight containers are metal or glass with rubber gaskets on the lids. Many small paper packets will fi t into a large-mouthed glass jar. Weigh the seed in the packets, then put them in the jar with an equal weight of silica gel, which turns from blue to pink as it absorbs moisture.

After a week in the container, the silica gel should be removed (it can be dried out slowly in an oven or microwave and reused many times) and the jar promptly resealed. Seed treated this way will retain excellent viability for a long time. If the glass or metal container is kept in a refrigerator or freezer, seed life is even longer.

I encourage every gardener in mild climates to give biennial seed-saving a try. For those of us who brave our more northern arctic winters, creating some sort of cold but not frozen winter storage space is necessary, following the same conditions needed for good winter-long root crop storage.

Preparing Leeks for Root Cellar Storage(Photo by David Cavagnaro)

David Cavagnaro is one of SSE’s advisors. He spent eight years as the Garden Manager at Heri-tage Farm.