Winter Sowing Your Seedlings

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With winter sowing, the question of when to start seeds is easily answered.
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Let Mother Nature wake your seedlings to help reduce the springtime hustle.
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Start seeds well ahead of the last frost and you'll be harvesting in record time.
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Learn how to start seeds with winter sowing.
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Milk jug cloches are easy and inexpensive to make.
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Create mini greenhouses out of milk jugs.
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Be sure to cut ventilation holes in your milk jug cloche.

It’s a problem we all face: Seed catalogs and traders have the coolest and most irresistible varieties of vegetables, fruits and flowers. You might even say your need for seeds borders on addiction. Sometimes you just can’t get all the varieties you want at the greenhouse, nursery or big-box store, and buying seedlings can get expensive fast, especially if you have a big garden to fill.

Some plants, like corn, peas and sunflowers, grow well enough from seed in the garden, but what about tomatoes, peppers, milkweed or hostas – plants needing a head start or special treatment to get growing? Sure, you can start them in your greenhouse or nursery – if you have the structure, room and money to do so. Starting seedlings in a sunny south-facing window sounds like a good idea, yet heartbreakingly pale, weak seedlings can sometimes prove otherwise.

Timing is crucial to transplant success. Tomatoes need eight weeks under lights, and peppers 12 – more if the air is cool. Petunias need even more time, but don’t start eggplants too soon, or they’ll become pot-bound and stunted. Then there’s the dreaded damping-off fungus, killing entire flats of seedlings. There seemingly has to be a better way – and there is.

Method to the madness

Courtesy of Trudi Greissle Davidoff, her “winter sowing” method makes successful midwinter seed starting easy, and she maintains a website devoted to it at Winter Sown. Her unique way of starting seeds eliminates the need for lights, heat sources and complicated planting calendars.

What exactly is winter sowing? The USDA defines winter sowing as “a propagation method used throughout the winter where temperate climate seeds are sown into protective vented containers and placed outdoors to foster a naturally timed, high percentage germination of climate tolerant seedlings.” Quite a mouthful.

Trudi’s approach is a bit easier to comprehend. Simply put, you start your plants outside – in winter. She describes a seed-starting method in sync with the seasons as well as economical, low tech and worry free. Using winter sowing, anyone can produce all the plants they need. All you need to get started is a bag of potting mix, some containers, labels, and of course seeds.

Rhyme and reason

Winter sowing works because temperate-climate plants – ones that grow in seasons like tomatoes, peppers, coneflowers and morning glories – all have something in common: They know when to wake up in the spring.

Depending on the plant species, some seeds rely on moisture slowly soaking into their hulls. Others refuse to sprout before they’ve been chilled for a specific number of hours. Some can’t begin to grow until frost has split their stony pits in half, while others are coated in chemical growth inhibitors that must be broken down before they can sprout. They all have another thing in common: They need to experience winter weather to get them going in spring.

Getting started

The winter sowing season begins with the winter solstice, or if you prefer, after the holiday festivities have passed. You don’t want to start too soon. Unseasonably warm late fall days can wake some of your seeds, inviting disaster. Take an afternoon to go through your stash of seeds, deciding what you want to sow and how many plants you think you’ll need. This will tell you how many containers you’ll need.

Let’s talk about containers. They can be just about anything, as long as they can hold at least 3 inches of soil, and can be easily cut and trimmed with a utility knife. Plastic pastry clamshell containers work well, as do Styrofoam restaurant soup cups with clear plastic lids. One-gallon milk jugs are ideal with a little modification. If you want something a bit more uniform in appearance, most nurseries and greenhouses sell 9-by-18-inch seedling flats and clear plastic domes. However, don’t try reusing seedling six-packs for winter sowing. The individual cells can’t hold enough soil to keep seedlings evenly moist.

Preparing your containers is simple. Turn each container upside down, and apply a strip of freezer tape to the underside of each. Label each strip with the plant type and variety, using permanent ink. The underside of the container will protect your labels from fading.

Next, cut some drainage holes in the bottom. A utility knife works well, but cut carefully, away from your body. Cut some vents in the container’s lid, and protect your winter sowings from trapped solar energy.

Fill each container with pre-moistened good-quality potting mix to a depth of at least 3 inches. Potting mix is the one area where you should spare no expense. Cheap mixes can become crusted and hard, they tend to sour, and can suffocate plant roots. Good mixes are light and loose, and hold sufficient water while still draining well. Choose a good professional mix high in peat moss and perlite, or make your own mix with equal parts perlite, peat moss and screen-finished compost.

Many potting mixes already contain small amounts of fertilizer, often timed release, but it really isn’t necessary for your plants given the short duration they will be in these containers.

Seedy business

Now, add your seeds. You can sow them as heavy-handed or as sparingly as you wish. You have all the time you need – all winter, in fact. If you prefer, lay each seed out precisely in its bed, equidistant from each of its neighbors, or simply scatter a veil of seeds across the flat. The latter is a quicker method, and your results will be just as good, if a bit thicker. Trudi confesses that some of her sprouted containers begin to resemble beds of moss. Cover the seeds with a layer of soil mix, about a seed’s own size in depth, and water them in gently.

There’s no rush with this step, as you really do have all winter to get it done. There are no complicated schedules to keep, no risk of burnt-out lamps or fried heat mats. You don’t even need to worry about the cat tipping containers, fungus gnats invading the living room, or damping-off leveling whole flats of plants. Just sow a tray at a time, or as many as you like, whenever cabin fever starts to get the best of you.

As you finish each container, take it outside to its winter spot, somewhere sheltered from wind and marauding animals and children. This may seem like harsh treatment for your little darlings, but remember, that’s just what they need for a good strong start in the spring. A thick blanket of snow won’t faze them. In fact, they’ll love it. Even if they freeze solid and water stands an inch deep over them for a week or two, they’ll be fine.

Wake-up call

As the days begin to lengthen and warm, your containers will thaw out. The seeds will wake and begin to grow, right on schedule. Overnight low temperatures will still be dipping below freezing, but there’s no need to panic, your seedlings will be just fine. Believe it or not, daytime highs are a bigger concern, threatening baked or steamed plants. Gradually cut the vents larger to release excessive trapped heat, until the lids are more vents than plastic.

By now, the seedlings are ready to be transplanted. They will probably be smaller than you are used to transplanting, but it’s OK. They’re ready for their new permanent locations. Even if they only have two or three true leaves, they can be moved to the garden.

By now, you’re most likely staring at thickly planted containers carpeted in green, wondering how you’re supposed to safely remove individual seedlings. It’s simple – you don’t. Instead, scoop out little clusters of seedlings, including as much soil as possible, and plant these entire clumps. Try to keep the clumps about a square inch. Trudi calls this the “hunk-o-seedlings” method, and assures there will be plenty and some to spare. Don’t worry about thinning them out until a week or so later.

Once you’ve transplanted them, treat your seedlings as you would any other transplants. Water them in, feed them lightly if you like, and provide a little shelter from the wind. If you used milk jugs, you can cut the top of the jugs off and use them as cloches. Once they’ve settled in, you can thin them out if need be.

Winter sowing is a simple, low-resource method for starting lots of seedlings. It works well for seasonal vegetables and flowers, and especially well for temperate fruits and shrubs. An added bonus of winter sowing flowers, especially ones with tiny seeds, is knowing your seedlings really are what you planted, and not a bunch of weed seedlings.

For more information, visit Trudi’s website, or join her Facebook group Winter Sowers. A word of warning, Trudi fully acknowledges that winter sowing can be highly addicting, at least as addicting as seed saving and collecting.

Make a Milk Jug Greenhouse

Winter sowers, and gardeners in general, are typically a frugal lot. We’re always looking for ways to reuse or repurpose throwaway items. One-gallon plastic jugs make perfect candidates for winter sowing containers. The plastic is soft, easily cut, and a decent size for a good crop of winter-sown seedlings. Follow the steps below to make your own one-piece winter sowing mini greenhouses.

1. Rescue a clear plastic jug from the recycling bin. Choose one made of translucent clear plastic, such as an iced tea or water jug. Many actual milk jugs are made of opaque white or yellow plastic, which will block sunlight, and are not a good choice.

2. Wash the jug thoroughly and let it dry. Discard the cap.

3. Using a sharp knife or sharp tipped scissors, punch a drainage slit in the center of the bottom edge of each side panel. Take care using sharp instruments, and always cut away from yourself.

4. Mark a line around the center of the jug (line will be horizontal), using a permanent marker. This is your line to cut the jug in half.

5. Starting at the label, cut around the jug along the line. Stop cutting at the other side of the label. If there isn’t a label, leave two inches uncut. This will serve as a hinge.

6. Turn the jug over and apply a piece of duct tape to the bottom for a label.

7. Write the variety and sowing date on the label with a permanent marker. You can also make a plant marker to put inside the container.

8. Fill the container with soil to within an inch of the cut, then sow seeds, and water them in.

9. Close the jug, and secure with a small strip of tape as a latch. Using a longer piece of duct tape, seal the entire cut line with two layers of duct tape.

10. Set it outside for the winter. After your seedlings have been transplanted, you can cut the top free to use as an impromptu cloche or frost cap.

Andrew lives and writes in southeastern Pennsylvania. He is a member of the Backyard Fruit Growers, and has been collecting too many seeds and plants for many years. He is always up for the challenge of trying a new gardening method, and has been known to work in the garden on New Year’s Day in a foot of snow.