If you’re a gardener with big plans for spring, you might give a new technique called “winter sowing” a try.
Winter sowing is a way to start seeds outdoors by essentially creating mini-greenhouses made of recycled milk jugs or even plastic bags.
Some seeds require cold stratification: That is, exposing the seeds to a period of cold conditions for several weeks, breaking their dormancy so they can germinate in spring.
The homemade greenhouses mimic natural conditions that provide the necessary cold stratification and expose the seedlings to sun and weather, without the need for grow lights. The result is strong, self-hardened plants ready to transplant in spring.
You are most likely to have success jump-starting the growing season for cool-season annuals, like pansies, alyssum and sweet peas.
Vegetables such as lettuce, spinach, kale, and broccoli are also good candidates for this approach. Native perennial plants, like milkweed and rudbeckia, also need to experience winter conditions in order to germinate.
Emma Erler, Homegrown NH host and lead horticulturist at Kirkwood Gardens, explains how to get started:
What you need:
- Plastic jugs or other transparent, covered containers. Milk jugs, 2-liter bottles, takeout containers, or salad mix containers can work well.
- Potting mix
- Tape for sealing and labelling
- Scissors or sharp knife
- Seeds
- Drill
1. Collect and wash containers. Containers should be able to hold at least 3 inches of potting mix and have covers that can be vented. Jugs and bottles will need to be cut in half with lids removed. Lids need holes cut in the top.
2. Make 4 to 6 holes in the bottom of the container to allow extra water to drain away. Add an optional water-permeable barrier to keep soil from washing away (a coffee filter, piece of newspaper, or landscape fabric).
3. Add potting mix, 3+ inches ideally. Moisten mixture thoroughly.
4. Plant seeds, ideally only one species or variety per container.
5. Cover containers and place them in a protected area in at least part sun.
6. Monitor containers periodically for dampness and germination.
Once seeds have germinated in spring, you’ll need to keep a close eye on conditions, opening containers if it warms up and moving them to the shade if necessary. During cold spells, close or cover the containers.
See you in the garden!
If you have a question for us, you can send us an email or voice memo to Homegrown NH@NHPR.org.
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
