Sunday, January 20

Winter sowing warms a gardener's soul

Many annuals, perennials, trees and shrubs can be sown successfully during January and February.

It was one of those head smacker moments -- those times when the light bulb goes on and you ask, rather sheepishly, "Why didn't I think of this sooner?" Every fall I'd carefully collect and thoroughly dry the ripe seeds of favorite native annuals and perennials from my garden. I'd dutifully mark plastic bags with the names of the plants and check the charts to see how long the seeds needed to be kept cold. Then I'd tuck them, packed in fine, moist sand, in the back of the refrigerator. After the proper interval, I'd plant them up in covered trays and finally sprout them under bright grow lights in the basement.

Then one year my wife casually commented, "Wow, it's just like you were growing them outside..."

Light bulb!

Winter sowing hardy annuals, perennials, trees and shrubs outside might seem counter-intuitive at first -- especially if you've gone to the expense and time of creating a warm, cozy indoor propagation area. But if you stop to think of it, it's perfect for the plants that need a period of cold to break their dormancy, or that just get a head start on the season by growing slowly in the deep cold of winter. And nature has been doing it successfully this way for some time now....

Many perennials, shrubs, alpines and desert plants need this period of cold, called stratification, to break dormancy. Not only does the cold suppress certain inhibiting chemicals that keep the seeds asleep, the natural winter freezing and thawing cycles will crack the seed coats to allow moisture to enter and start germination.

First, make sure you have the right kinds of plants. As a rule of thumb, choose ones that have proven themselves hardy in our area. When I'm trying something new, I'll save out a few seeds, cold treat them in the fridge and sow them inside just to be safe.

Second, gather some containers. I use anything from plastic gallon milk jugs or juice cartons to "chicken domes" -- those plastic deli domes that roast chickens are sold in. Butter tubs, brownie trays, anything that has -- or can be covered with -- a transparent dome, lid or plastic wrap will do. Wash them thoroughly and sterilize them with a solution of nine parts water to one part chlorine bleach before allowing them to air dry.

Next, pop a few drainage holes in the tray and transpiration holes in the cover with an ice pick. Alternately, you can use a soldering iron or the tip of a hot glue gun to melt some openings. These holes are vitally important. The soil must be drained to remain moist but not wet. And the dome, essentially a micro-greenhouse, can fry delicate seedlings even in the winter if it isn't ventilated.

Fill the tray with about three inches of good quality, sterile potting soil that's moist enough to feel like crumbly brown sugar. Don't use soils that have fertilizer already mixed in -- the chemicals can burn developing roots and shoots later on.

Sow the seeds over the top of the soil. Big seeds can be planted by hand, but the really little ones should be mixed with some ultra fine sand and sprinkled evenly over the soil with a salt- or cheese-shaker. Tamp the seeds lightly to insure good contact with the soil. Then cover the tray with its dome, lid or plastic wrap cover and seal it tightly with tough packing tape. Label the tray to identify the seeds inside and you're ready to move them out into the cold, cold world.

Choose a full-sun location where the trays will be undisturbed. An open cold frame or open, unheated greenhouse is perfect. But the south side of the house, away from falling snow or roof runoff, is fine. You should begin to see condensation forming on the inside of the clear covers almost immediately. This means there is sufficient moisture in the soil.

Now all you have to do is wait. As the days grow longer and the weather warms, nature's wisdom will start pushing tiny new seedlings up in their proper time. Check the soil for sufficient moisture when the temperature is above freezing, then reseal the covers tightly. Make the transpiration holes slightly larger as the plants grow, eventually removing the covers completely and transplanting your seedlings into the garden.

Once in the ground, these tough little troopers need a very dilute liquid fertilizer feeding, about 10 percent of the label recommendation, once a week. Increase the strength of the fertilizer weekly until, in about two months, you're feeding them at full strength.

I still have my elaborate propagation trays and bottom heat mats and grow lights cooking away in the basement during the winter. Lots of the flowers and vegetables I like to grow need that cushy head start to prosper in our area. But it's a real joy every time I see the first sprigs of winter-sown green showing up in the still-frigid days of early spring and knowing all I needed to do for them was let nature take her course.

For a list of plants that are good candidates for winter sowing in our area, click here.

Active in the horticultural industry since 1994, Glen O. Seibert is a former editor for Garden Gate magazine and now works as a writer, landscape designer and self-professed "gardening media mogul."