Winter sowing is a method of growing seedlings. Instead of keeping the seedlings inside
until danger of frost has passed, the seeds are sown in containers that are left outside.
The containers act as mini-greenhouses and the seeds germinate and grow when the
conditions are right for them to do so.
Interested in starting to sow seeds outside for your garden this year? Check out these simple instructions below from the Calgary Horticultural Society.
What you need
Several types of containers work well for this method, including the following:
- 4 litre milk jugs
- large clear pop bottles
- 2 litre milk jugs
- large plastic salad containers
- or anything other container that can hold three or four inches of soil, is covered, and clear or white to allow light in
• Drill or awl to poke drainage holes in the bottom of the container
• Box cutter knife for cutting slits into the top of the container to let rain and snow in
• Permanent marker to record what was planted in each container
• Clear packing tape or duct tape
• Potting soil
Preparing the containers
• Rinse the containers out with hot soapy water.
• Make 3-4 drainage holes in the bottom of each container.
• Cut 4-5 slits in the top half of the container to let rain and snow in.
• Cut milk jugs or pop bottles in half, leaving a hinge on one side. Having one side
hinged makes it easier to tape the container back together.
• Fill the containers with 3-4 inches of potting soil. Water the soil and allow the
container to drain.
• Sow one type of seed per container. Lay the seeds on the top of the soil and
gently press them into the soil. Cover with soil as directed by the seed packet;
some seeds do not need to be covered.
Labeling and Taping
• Number each container and label it with the type of seed it contains.
• Use the packing tape or duct tape to tape the milk jug or pop bottle together.
Placing the containers outside
• Place the prepared containers outside and leave them in a partially sunny spot to
be snowed and rained on. Be patient and wait for your seeds to germinate! As
the plants begin to grow, the slits in the containers help the seedlings get used to
wind and weather. This helps them grow strong and hardy. Many Calgary
(Alberta, Canada) gardeners have had their seedlings make it through -10C
(14F) in milk jug containers!
Watering and Transplanting
• If it looks like the soil might be drying out later in the spring, you can give the
seedlings a drink by carefully pouring water into the top of the container.
• Leave the lids on the jugs until all risk of frost has passed
• If it is too difficult to separate the seedlings, plant them in small clumps and then
thin them out as needed.
When to Winter Sow
• Start seeds that need longest to germinate in January/February (perennials,
trees, shrubs and hardy annuals)
• Start seeds that aren’t as hardy later: annuals in March/April & tropicals in April/May