Winter sowing perennials has been around for several years now, and is a great way to start native plants or a lot of plants without the investment in lights, seed-starting trays and the other equipment needed to start seeds indoors.
If you have not heard of it before, winter sowing involves planting seeds in plastic containers, such as gallon milk jugs or the clam-shell containers from takeout food joints, to create mini-greenhouses. You can plant them anytime during the winter and then set them outside no matter what the weather. The theory is that the seeds know when to sprout and they will come up at the right time. Many perennials require “cold stratification” in order to germinate. This means they germinate only after their seeds have gone through cycles of freezing and thawing.
The freezing and thawing helps break open the seed coat. Here’s a long list of perennials that require cold stratification, but among those familiar to northern gardeners are perennial geranium, turtlehead, hardy hibiscus, catmint, rudbeckia and sedum.
What are the advantages of winter sowing? 1) It gives you something to plant in the winter. 2) It’s a good way to start seeds if you do not have enough space in the house or a good light source for indoor seed starting. 3) The seedlings are acclimatized to outdoor weather early on, and are less likely than indoor seedlings to faint when placed outside. Winter sowing works best on perennials that are hardy to our region, though with some modifications related to timing you can also winter sow vegetables.
Northern Gardener first wrote about winter sowing in 2009, and you can read that article in the online archives. It gives a great overview of the process and offers more ideas for which plants grow best in winter sowing containers. On these super cold days, just thinking about planting for next year lifts a gardener’s spirits!