Several species about to go into the refrigerator.  You can grow some unusual things when you grow plants from seed.  I didn't even know there was a Calycanthus fertilis (native to the southern Appalachians) until I saw seed of it available.

Several species about to go into the refrigerator. You can grow some unusual things when you grow plants from seed. I didn’t even know there was a Calycanthus fertilis (native to the southern Appalachians) until I saw seed of it available.

In late February we’re all done with winter and ready to hit the garden, but of course there’s not a great deal that can be done outside with two feet of snow on the ground and subzero wind chills. But spring is on the way nevertheless, and if you have the desire, you can start this year’s garden right now: in the refrigerator, by cold-stratifying seed.

Most plants native to the Northeast don’t want to germinate in the fall (when they would soon be killed by winter), and they ensure spring germination by requiring a relatively lengthy period of dormancy under cold, damp conditions. The dampness is essential – water seems to start the seed’s clock – and the period of cold required varies by plant. Most growers satisfy these requirements by planting such seeds in the fall, and letting them go through the natural process called winter, when there is ample coldness and dampness. But if you have ever tried sowing seeds in the fall for spring germination, you know that many things can befall them in those six months in the ground (rodents in particular). For years I was told that pawpaws (Asimina triloba) were easy to germinate, and I would plant some every fall. But the large seeds are rodent favorites, and each spring I would have nothing left in the soil where I had planted them. I can’t smell a pawpaw seed in the ground, but apparently mice and voles can.

But it turns out that you can replicate the germination requirements for these native plants with a refrigerator, and growers have found that you really don’t need to keep the plants stratified (the term for leaving plant in a damp medium for a period prior to germination) for the whole winter. Most growers find that sixty days is enough, and Prairie Moon, a large nursery which has probably gotten pretty good at growing plants from seed, reports that many plants will begin germination after only thirty days of cold stratification. Either way, if you cold-stratify your plants in March, you can take them out in May ready for planting.

You can put the seeds in typical seedling trays, but only if you’re willing to dedicate a large amount of refrigerator space to seed stratification (and if you don’t live alone, there may be someone else in the house with opinions on this issue). The most efficient way is to take the seeds and put them into a small ziploc bag with a small amount of planting medium. Almost any medium that will hold moisture and keep the seeds continually damp will work. I like sand for this purpose, as it works and is cheap, but vermiculite or seed starter mix or even soil (if you can find any that isn’t rock-hard by now) will work (soil is the least desirable because sterility is typically desired for long-term storage of damp seeds, but I have used soil in the past and gotten good germination. Probably tissues or newspaper would work in a pinch too, though I’ve never tried it). All you need is enough material to maintain constant contact with the seeds in the bag. Add water to keep things damp but not really gooey, label the bag, and in the refrigerator it goes. The freezer will not work: the seeds have to be cold but not frozen (around 40 degrees is typical, but any refrigerator conditions will work). Take the bag out after the minimum cold stratification period is over and sow the seed in seed flats or pots or garden beds outdoors.

Of course you need to have seeds onhand if you want to cold stratify them. I tend to snip seeds off desirable plants and put them in envelopes over the course of the garden year, and so I have them on hand when I get the gardening bug in late winter. But seed is also widely available from mail-order companies on the internet, and seed is an extremely cheap way of building up a garden. A packet of seeds – which can range from twenty to a thousand seeds – rarely costs more than three dollars. For twenty dollars in seeds you can grow thousands of plants – more than you’ll know what to do with. I use these mail-order seed sources for rare and unusual plants that are difficult to find. The variety offered is truly incredible: this past year I was impressed by the wild carrion-flower (Smilax lasioneura), a climbing vine with interesting spheres of green flowers. Prairie Moon Nursery had carrion-flower seeds for sale, though the plant was so rarely grown they didn’t know how to germinate them. The fact that they had seeds of such a non-commercial plant at all impressed me. Not many people are clamoring for vines with green flowers that smell like rotting meat.

Asclepias exaltata, Poke Milkweed.

Asclepias exaltata, Poke Milkweed.

If you make your selections now, you can have stratified plants ready to start growing by Memorial Day, when the Catskill growing season really begins. This year my growing plans focus on three genera of plants: Iris, Asclepias (milkweed), and Amsonia (bluestar). All three genera show very strong deer resistance, and since the amount of space I have inside deer-fencing is limited, I’ve been looking for ways to offer area pollinators some kind of herbaceous layer outside my fence in this era of rampant deer. I’ve grown Iris and Asclepias from seed before – they’re very easy – and I have a friend who has grown Amsonia without difficulty as well. All three genera also contain a fair number of species, so you can pick species for wet spots or dry spots, shady spots or sunny spots, and for different soil types. I’m growing Asclepias exaltata, Poke Milkweed, this year from seed: it’s a Catskill-native milkweed that likes shady spots. It’s not very showy, and is not likely to become a nursery favorite anytime soon, but it adds a little diversity to my woods, and deer don’t seem to eat it (while monarchs do like it).  Growing plants from seed increases diversity in two ways: first of all, by making available plants which are not found in the nursery trade, and secondly, because each seed is a unique individual with its own DNA, whereas many nursery plants are cultivars, i.e. a particularly likable clone.

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  1. / Growing Plants From Seed.
    February 23, 2015

    […] A piece I wrote for the Catskill Native Plant Society on cold stratifying seed. […]