Published Mar. 6, 2016, Wyoming Tribune Eagle, “Winter sowing starts garden at perfect time.”
By Barb Gorges
When I asked her for tips on starting perennial seeds this spring, Laramie County master gardener Michelle Bohanan said, “winter sowing.” I soon discovered it is an increasingly popular concept and practice.
Winter sowing is what our native and other temperate zone plants do naturally. After they set seed, the flowers and fruits dry. Within months or years, they either shatter and release the seeds, a messy bird picks at them, or the wind blows them. You might shred a few dried flower heads yourself from time to time.
The seeds eventually come in contact with the ground where they are subjected to moisture and cold. That, and the cycles of freezing and thawing, eventually break the seed coat which is necessary if it is tougher than the strength of the seedling.
Surprisingly, many seeds require light to germinate. Day length, or cumulative solar warmth, tells them when it is safe to sprout.
With our occasional spring snowstorms, it’s good that not all seeds, even of the same variety or species, require the same exact amount of light and heat. If the first up are frozen out, the slower germinating fill in behind.
Of course, the plants that have winter sowing down to a fine art are the weeds.
The problem with merely sprinkling seed over your flower bed is that seed is expensive and you don’t know how hungry your local birds and mice are going to be.
It occurred to New York state gardener Trudi Davidoff to safeguard her winter sowing by seeding in shallow, covered containers she set out in her garden. In spring, there was no need to harden off the seedlings since they were already acclimated to the outdoors. She merely transferred them into her garden. Another benefit? No need for grow lights or heat mats. She’s been spreading the word since.
How to winter sow
I visited Bohanan on a nasty day in January with half a foot of snow on the ground. I brought along a translucent plastic gallon milk jug and a little packet of alpine aster seed I’d received in a seed exchange.
With a pair of heavy-duty scissors, Bohanan punctured the jug just below the handle and cut all the way around, creating a 4-inch high pot and a separate cover. She put in about 3 inches of her favorite commercial potting soil, already moistened.
Next, she spilled a couple dozen seeds onto a plastic container lid and with a toothpick, sorted through them, kicking out any unfertilized seeds. They look lighter because they don’t have the germ of the seed needed for germination.
Like many small seeds, these require light, so Bohanan gently pressed 16 into the soil but didn’t bury them. Then she forced the upper half of the milk jug, upright, into the bottom half to protect the seeds, leaving off the jug’s cap.
In other, wetter climates, the top and bottom can be slashed to allow snow and rain to water the seeds and then drain, but in our drier climate, Bohanan has had, over seven years, good results without making additional openings.
However, I found I had to puncture the bottoms after the snow on top of my jugs began to melt.
On the Internet, a search for “winter sowing” shows many kinds of recycled containers. The bottom needs to be at least 3 inches deep for the soil and the top needs to clear the soil surface by at least 2 inches. The top also needs to be clear or translucent. You provide adequate ventilation and drainage openings as needed.
On the jug in permanent marker Bohanan wrote the name, source and number of seeds and the date of planting.
Back at home, I put the milk jug in a snowdrift on the northeast side of our back fence. While I wait for spring, I’ll empty more milk jugs and try planting more seeds.
Bohanan already had 35 jugs going and figured she was only 25 percent of the way through her winter sowing plans.
This technique is easier than my experience last year sprouting orange butterfly weed—a type of milkweed. I had to leave the seeds, planted in moist potting soil and covered with plastic, in my refrigerator for 6 weeks to achieve “stratification,” the term for this cold treatment. Other seeds need scarification, scratching a break in the seed coat, and this winter sowing method can help.
While seeds left lying on the ground require no help from us, ones in containers do.
Bohanan’s milk jugs have the opening at the top, plus the gaps where the upper part of the jug is pressed into the bottom, that allow for some snow and rain to seep in and some heat to escape when it warms up in the spring. She forgoes slits in the bottom because she puts some jugs in her unheated sunroom and would rather not have them leak on the floor.
However, she does check her jugs regularly to make sure they don’t dry out, especially the ones under cover of her hoop house. She can tell by the lighter color of the soil (although this doesn’t work for all potting soils), or she can lift the jug and tell by the weight if it needs watering.
Knowing how much water to add might be a trick, and if you think you might be prone to overwatering, you should probably add bottom drainage openings.
When the weather gets warm, to keep seedlings from baking, it is necessary to pull the top off and prop it on the bottom diagonally or even remove it entirely during the day.
Timing and location
All of this still sounds easier and cheaper than setting up lights or buying starts next spring. With our last frost nearly three months away, there is enough time to accommodate even seeds that need 8 weeks of cold.
But figuring out where to put your jugs is also important. Placed along the south-facing wall of your house may cause some seedlings to sprout too soon. Along a north-facing wall may delay them. But the mini-greenhouses are easy to move. Just experiment.
What to grow
Try native perennials from our northern temperate climate, Zone 5 or colder, especially if you are turning your lawn into bird, butterfly and bee-friendly habitat. Popular flowers include varieties of penstemon, coreopsis, milkweed and gaillardia.
Try cold-tolerant vegetables from the cabbage family, herbs and flowering annuals, but probably not slow-starting annuals like petunias. It would take all summer for them to finally bloom.
The seeds of tropical plants, like tomatoes, eggplants and peppers, may also get started too late to produce before first fall frost. Instead, see tomato growing advice archived at www.CheyenneGardenGossip.wordpress.com.
Winter Sown, www.wintersown.org: Trudi Davidoff’s site.
Dave’s Garden, http://davesgarden.com/guides/pf/ws: Gardeners all over the country have recorded their success winter sowing a variety of plants, but be aware of what zone they report from.
Alplains, http://www.alplains.com/: This catalog specializes in native plant seeds and has essential propagation information. However, use the following website to translate the Latin names.
The Missouri Botanic Garden’s Plant Finder, http://www.missouribotanicalgarden.org/plantfinder/: This is one of Bohanan’s favorite sources of information.
Typical native perennials for the Cheyenne, Wyoming area: Blanketflower, Gaillardia spp.; Gayfeather, Liatris punctata; Tickseed, Coreopsis spp.; Beardtongue, Penstemon spp.; Black-eyed Susan, Rudbeckia spp. All photos by Barb Gorges.