Written by OzMG Mary Hotchkiss
Reprinted (with updates) from Spring 2020 “The Best Dirt”
It started with seeing a gallon milk jug by the door outside Lasata’s greenhouse. I asked Judy O’Connell, OzMG’sformer Lasata project lead, about it. She explained that residents started winter sowing lettuce in jugs in March. When I peered inside the jug - lettuce! That “AHA moment” turned into my primary method of starting cole crops (lettuce, arugula, kale and swiss chard) as well as perennial flowers (Delphinium, Bells of Ireland), annual flowers (zinnia, snapdragons), basil, peppers, and tomatoes!
Winter sowing is a method of starting seeds outdoors in winter in containers that act as “mini greenhouses”. I start planting seeds that require a period of cold stratification and cole crops on or near Super Bowl Sunday. (Not exactly scientific but it works for me!) All of my other seeds get planted on or near St. Patrick’s Day, although they can be started as late as April/early May. After the weather gets warmer, it is no longer referred to as winter sowing since the period for “cold stratification” is over.
What You Need to Get Started
I have mixed my own potting soil but usually use potting soil that is ready-to-use. I try to buy the potting soil in fall so it isn’t frozen (sometimes it is on sale too!). I once ran short and bought potting soil in January that was outside of the hardware store. Lesson learned.
In December, I ask family members to start saving plastic gallon (or larger) milk, water, distilled water, or juice containers. I also began using larger yogurt containers and place a vented plastic bag over the top – it works great for my basil! You can use any container that is translucent enough to allow light to pass through. It will need drainage holes, a lid, and ventilation holes. Additional options include, but are not limited to, water or liter soda bottles, take-out containers, disposable foil pans with plastic covers, clamshell containers, disposable beverage cups, plastic tubs, and plastic totes. I haven’t had much luck using the clamshell containers – they seem to dry out quickly and I haven’t used the plastic tubs or totes.
I use a cordless drill with a 1/2” drill bit to make holes in the bottom of the containers. The gallon containers get four holes, the 2-gallon containers get six holes. After drilling the holes, I cut the containers at 3-4” from the bottom to make room for at least 3-4” of potting soil. I cut (using a utility knife) all the way around the container leaving an “uncut” portion for the “hinge”. When finished, line up the containers, fill with 3-4” of potting soil, and water evenly.
Next, get the labels ready. For years, I have been writing the name of the seeds on a piece of paper with a Sharpie and then “rolling it up” to put inside a medicine/pill container which I attach to the handle with a zip or cable tie. This year I used a “cattle pen” (what is used to put numbers on the tags for cattle/cows). I wrote the seed name on duct tape and taped it to the side of some of my containers. According to others who do winter sowing, the cattle pen does not fade. Some put the label on the bottom of the container and others put it on a piece of plastic (from old blinds) and put it inside the container.
It’s time to plant. Plant seeds close to the surface. Do not follow directions on the packet. I put a small indentation in the soil with a popsicle stick and put a seed in and lightly cover them. For tiny seeds such as basil, I sprinkle them over the soil and tamp them down.
After the seeds are planted, I put a very thin layer of potting soil over them. Then I “put the top down” and seal the container with duct tape. If you are using a container that had a cap, leave the cap off. That’s how water gets in from melting snow or rain and that's how the “hot” air will escape if there’s too much condensation in the container. If you are using the larger yogurt container you can put a plastic bag (such as a “Ziploc”) over the container.
Line your containers up outside and leave them there! I place mine on the south side of our home. Depending on the weather, there could be a lot of growth by April. You may need to move the containers to the east side or a shady area until you can plant your young plants into the ground. When the weather warms up and the seedlings are tall but not yet ready to transplant, I “prop open” the container to provide additional circulation. You will find yourself anxiously checking to see if anything is coming up. As you check, if there has not been sufficient rain or snow to provide moisture you MAY need to provide some water. I have lightly sprinkled water through the opening. You must be “gentle”, or the seeds will wash away!
As a write this (May 13, 2020) my cole crops are ready to move into the garden and planters. It has been a strange winter and spring, so tomatoes are lagging, but I am not giving up hope. The flowers (perennials and annuals) need a bit more time. With the warm weather coming, I hope they will be ready by Memorial Day. I was never able to get Delphinium or Bells of Ireland to grow when I bought plants from a nursery. I winter sowed these plants four years ago and they are strong plants – and come back every year.
There are many advantages to winter sowing:
It is simple to do. I have an annual “winter sowing” get together with the children that used to live next door. They pick out their flower seeds in January, I order them, and we plant them along with some basil seeds in April.
It’s efficient. You do not have to run grow lights for weeks at a time as when starting seeds indoors.
You don’t need to worry about having leggy seedlings because they are planted and grown outdoors. NO DAMPING OFF!
There is no need to harden off the seedlings as they are already acclimated to outdoor conditions. They are ready to plant whenever the outside temperature has sufficiently warmed.
Saves space inside for plants that need to be started indoors prior to planting outside.
It allows someone who doesn't have the room, a grow light set-up, nor the window space available indoors to start seeds successfully.
Prevents seeds from being washed away or eaten.
It gives you something to do gardening-wise during the winter/early spring. It was therapeutic this year, which is why I have more containers than ever!!!
I started winter sowing in 2015 with six milk jugs. This year I have a record number of containers of various shapes and sizes with four different varieties of kale, four varieties of lettuce, and many new flowers and tomatoes as well as my usual flowers.
Wintersown.org is a good resource. It was established by Trudi Greissle Davidoff, who was the originator of the winter sowing method in 2000. There are numerous Facebook groups related to winter sowing that are good places for gathering information and hints. Thank you, Judy for getting me started with winter sowing!