Winter Sowing, Step by Step

It really surprises me when I mention winter sowing to another gardener (especially one in Chicago) and they aren't familiar with the concept. Winter sowing has probably saved me $200 worth of perennials in the two years I've done it.

When you pay for a perennial, what you're paying for is the two to five years of space, water, and fertilizer (and advertising, if you want to go that way) that the grower has had to expend to grow the plant. The perfect way to circumvent those costs is to grow your own perennials from seed. A lot of perennials grow to a decent size in a year or two, making this an excellent use of resources for people who have the time to care for baby plants (a cumulative hour or two per week). The problem with doing this is that a lot of perennial seeds, especially hardy perennial seeds, require a long cold period in order to germinate (sprout). Winter sowing provides an excellent solution.

For those unfamiliar with the concept of winter sowing, it has a website, but the idea is this: Most of the time if you want to grow perennial seeds you've got to give them some time in the fridge, which (a) housemates complain loudly about and (b) takes up valuable fridge space. In Chicago, the solution is sometimes to just plant the seeds in the ground in fall and hope for the best, but a lot of seed gets lost, eaten or just plain forgotten this way. The winter sowing solution is, for many, milk jugs.

To winter sow, you just sow your seeds in an enclosed but ventilated container, stick them outside in December or January, and forget about them 'til thaw. Milk jugs provide excellent containers for winter sowing - they're tall, so there's good air movement for the growing seedlings, they're transparent, so good light, they're cheap (if you like milk), and they're easy to cut. Here's how to winter sow with milk jugs, broken into photographed steps to make it nearly foolproof. After the step-by-step, read this list of perennials to winter sow in Chicago (or elsewhere in zones 4 & 5).

How to Winter Sow (with Pictures)

An illustrated guide to your materials.

You'll need:

• seeds that must be chilled to germinate (my list of good winter sowing seeds)
• an empty, rinsed plastic gallon jug (it doesn't have to be milk, it just has to be tall, wide & transparent)
• a good quality seed starting mix, slightly moistened if need be
• duct tape
• scissors
• a knife or saw. A saw is better, if only because plastic can be tough on the blades of some knives
• a spray bottle
• OPTIONAL: a bowl into which the jug will fit without tipping over, for drainage

Step 1. Cut the jug in half with the saw, so that you've got the top and the bottom of the jug in two pieces. This can be difficult - try pinching an edge between your fingers and sawing at the fold. Start from just under the jug's handle, and make sure that the bottom half is at least four inches tall, otherwise there won't be enough space for the seedlings' roots.

Step 2. Now you want to create drainage and aeration slits. Flip over the bottom of the jug, and, on each edge, create a large slit. Try not to cut the bottom completely open, but if you do it's not a big deal, just make sure to support the bottom when you bring it outside and label the jug with a warning. Then take the top and make at least two large slits in that. Unfortunately I didn't snap a picture of the aeration slits, but they're pretty much the same as drainage slits. Oh, and try not to cut your fingers. Very important.

Step 3. Now flip the bottom right-side-up, fill it with soil, and sow your seeds. Make sure to follow planting depth instructions you got with the seeds, or look them up. Water the sown seed with the spray bottle before you put the top back on.

Step 4. This is the part I have the most trouble with. Next, you have to attach the bottom to the top with duct tape. You have to make sure it's sealed all the way around. I normally take a strip of tape and start with one side of the jug, sealing the jug side by side, since it's pretty difficult to seal it perfectly with one strip of duct tape. Those dang dimples are the worst. After the jug is sealed shut, make sure to label it! You don't want spring to come around and leave you with no idea what those cute little seedlings are. I also mark my jugs with sowing date and seed source, to make sure I don't get big batches of bad seed.

Step 5. Stick the jug outside. Find a nice sunny but protected spot. Southern exposure porches and decks are nice, but any bright little cranny on the east, south or west side of a building will do. In Chicago, the singular issue with the milk jugs is that they're light, and they tend to get blown away in early spring windstorms. In winter they're typically frozen down with ice, but once it all thaws, watch out. In spring, I press the jugs up next to each other and secure the line with a brick or cinderblock on either side, which works fine. You can also use chairs, tables, rocks, flowerpots, slats of wood, whatever's heavy enough.

Ta-dah! All done. The first time, this can take fifteen or twenty minutes, but now I can do it in five, if it's a small number of seeds. After the thaw, seeds take from a week to six months to germinate, depending on the species. After you take them out of their jugs, winter sown perennial seedlings should usually be grown to a good size in gallon-size pots for a year. Next, read my list of good and bad perennials to winter sow.