It is widely acknowledged that a healthy and sustainable landscape benefits the environment. Yet the availability and cost of local native plants can present a challenge to the home gardener. There is, however, an easy and economical means to propagate perennial native plants from seeds – Winter sowing is the answer!
The Method
Trudi Davidoff developed the winter sowing method over 20 years ago in collaboration with the USDA. The purpose was to establish winter sowing as a viable plant propagation method. It is defined by the USDA as “A propagation method used throughout the winter where temperate climate seeds are sown into protective vented containers and placed outdoors to foster a naturally timed, high percentage germination of climate tolerant seedlings.” Simply create mini greenhouses with recycled plastic containers that allow light. Plant the seeds and wait patiently through winter’s natural stratification process with freezing temperatures, ice, rain, and snow. Containers protect seedlings from downpours, weed seeds, unwanted plants, four-legged critters, bugs, and birds.
Plan for Bounty
Winter sowing yields an excellent germination rate. After my first year I soon found the importance of developing a thorough landscape plan to accommodate new seedlings when around 100 American hornbeam (Carpinus caroliniana) saplings sprouted from a few small containers. Other considerations for transplanting seedlings are:
- Soil testing is recommended for planting areas. Contact your local Cooperative Extension office.
- Sheet mulching in the fall to prepare your beds for spring planting.
Plant Selection
Perennials, many herbs, hardy and half-hardy annuals, cold hardy vegetables, shrubs, and trees are all good choices for winter sowing. Which vegetable and flower seeds to use for winter sowing depends on the length of your growing season and how long it takes the plant to reach maturity. Tender annuals and heat-loving plants such as tomatoes and basil can be sown using this method but are planted later. It pays to research your desired plants to determine their needs. Of course, tropical plants are not recommended for winter sowing.
Suggested winter sowing plant lists are available through the links in the resources at the end of the article. Some lists give the zones appropriate for the plant. Albemarle County Virginia is in Zone 7a.
Winter sowing provides abundant opportunity to replace non-native and invasive plants. Native plant habitats are more beneficial to our ecosystem than non-native plants as they promote healthy populations of pollinators, beneficial insects, birds, and other wildlife. For a wealth of information on this topic in Virginia refer to the following links:
- Why Natives? from the Virginia Native Plant Society.
- Native Plants for Northern Piedmont — Plant Virginia Natives makes it easy to identify plants appropriate for your existing site conditions by utilizing their section on Right Plants, Right Place.
- Albemarle County Recommended Native Plants is a relevant database for determining if a particular plant will thrive in your conditions, and it includes the surrounding counties. It allows you to search for plants by type, recommended use, plant needs, and plant characteristics and includes height and spread estimates as well as bloom colors and bloom times by month.
- Native Plants for Conservation, Restoration, and Landscaping (virginia.gov) is another great tool.
Germination
Seeds that require stratification are especially suited to this method; however, almost any seed will sprout and flourish if you follow some basic guidelines and the proper timetable. To germinate, seeds need the correct light, temperature, moisture, and air. Some seeds will sprout easily and quickly, others will need a full winter before sprouting and others will require several seasons. Some plant species will require special treatment such as scarification or planting immediately or keeping moist in a container after ripening to prevent the seed from drying out. For a primer on what some familiar native seeds need for germination see:
- Growing in the Off-Season – Native Perennials from Seed – Ecological Landscape Alliance (ecolandscaping.org)
- Seed Germination Database – Perennials(hort.net)
- Germination Requirements for Annuals and Vegetables | Horticulture and Home Pest News (iastate.edu)
Look in seed catalogues, germination guides, or on a seed packet for the seed’s germination requirements. Take note of the date to germination (DTG) and the date to maturity (DTM). The germination code on a seed packet indicates sowing instructions (conditions) needed for that specific seed. Some seed companies have a germination code for each plant they offer for sale.
Collecting Seed
Gathering, collecting, and organizing seeds is one of the most enjoyable aspects of this method. Purchased seeds are a reliable option, but it is good practice to search on-line for seeds using the botanical name to be sure you are getting the right seeds. For instance, instead of searching for wild bergamot, search for Monarda fistulosa. Many winter sowers swap seeds locally with friends or through an online group.
Organized seed swaps are available through public libraries or organizations like the Ivy Creek Foundation. Native plants already growing successfully on your property can also provide a plentiful source of seeds. Most seeds are mature when the fruit, for example a tomato, is ripe or for perennials the seeds are hard, brown, brittle, and dry. Generally, gather seeds that are dry and ready to harvest, and please leave plenty for the birds and insects and other critters who depend on them.
Preparing Containers and Soil
A vast amount of information already exists on how to prepare containers and soil, so this topic will not be covered in detail. Many people use milk jugs, but I prefer to use clear recycled salad containers with lids and plenty of holes as it simplifies the process. It is easy to leave the lid off on warm days and close it at night. Be sure your potting mix is damp, but not soggy when you plant. Add at least 3-4″ of soil to the container and be sure you will have enough head room for the seedlings. There are webinars and articles at the end of this article that give step by step instructions, should you decide to try this method of sowing seeds. The following Garden Shed article has information for starting common milkweed (Asclepias syriaca), butterfly weed (A. tuberosa), swamp milkweed (A. incarnata), and whorled milkweed (A. verticillata) from seed using winter sowing: Starting Milkweed From Seed | Piedmont Master Gardeners.
Sowing the Seeds
Create a schedule for your winter sowing. Most natives and hardy annuals can be sown any time after winter solstice in the Northern hemisphere, usually on December 21 or 22. Tender annuals can be started in March to April, but cover the containers when frost is expected. Wait until longer for heat-loving plants. Early planting will not produce larger plants. You can experiment and plant some seeds earlier and save the rest for later when you are certain they will be safe from freezing temperatures. Last year I planted tomato seeds on March 16, and they germinated right on time, but I did have to protect them from frost.
Tiny seeds can be mixed with sand to make them easier to spread out in the planting container. If you are uncertain about how deep to plant the seeds, look up that particular plant. Be sure to label your containers unless you like surprises. Set the containers above ground to allow for drainage and reduce slug infestations. Avoid areas that prevent rain, or invite too much rain, such as under a gutter that overspills onto the containers. If your containers are under a tree be sure to move sun-loving plants to full sun when the trees leaf out.
Seedling Care
Watering is rarely necessary, but do check periodically to see if the soil is moist. There should always be condensation inside the containers. A pump sprayer, or shower/mist setting on the hose nozzle is helpful for watering should the soil dry out. Watering from below is another option that prevents disrupting tiny seedlings.
Remove the lids or open the tops of containers on warm days in the spring. If temperatures climb too high, the plants will succumb to the heat. Wildlife can be a continuous threat. Hardware or wire cloth can be used once the containers stay open to keep squirrels and other wildlife out.
When seedlings have several true leaves, it is time to transplant. Transplanting with a dinner fork is useful for scooping seedlings out or if the seedlings are packed in tightly, you can use the “hunk of seeds” method by cutting them apart with a knife. Tender plants can be protected by a row cover if frost is a threat. Keep your transplants well-watered for the first year until they get established.
Conclusion
Winter sowing enables gardeners to reach goals much more quickly and economically by producing copious numbers of strong plants that do not need to be hardened off in the spring. Healthy native plant populations can easily be established to protect our water sheds from excessive runoff. The productivity that results from winter sowing can also be a catalyst for reducing food insecurity, producing a more sustainable landscape, and providing for the needs of pollinators, beneficial insects, birds, and other wildlife.
Whether you are a gardening novice, professional horticulturist, or somewhere in between, you should find this method to be easy, productive, and enjoyable. Some gardeners call it a healthy addiction!
SOURCES:
Featured Photo: Lisa Rittenhouse
All the Dirt on Winter Sowing | 24-minute webinar by University of Maryland Extension Charles County Master Gardeners
Winter Sowing – YouTube | 1 ½- hour webinar, hort.net
Winter Seeding – A Shortcut to Spring? | Extension (unh.edu)
Winter sowing: How I get a jump start on my summer flower garden – Maryland Grows (umd.edu)
winter sowing method | NAL Agricultural Thesaurus (usda.gov)
Winter Sowing | Buncombe County (NC) Extension Master Gardener
