Winter Sowing for Spring Blooms

posted in: Local Conservation, Plants | 0

With New England currently buried under our first real blizzard of 2022, spring flowers may be the last thing on your mind. Even so, the freezing temperatures of January and February are a great time to sow seeds of native plants for yourself, friends, family and wildlife. By planting seeds now, and then placing them outside for the duration of winter, natural processes will take over from there. Most seeds require a cold period (stratification) to germinate, and seeds with a tough outer seed coat need scarification (small cuts in the outer hull). Our New England winter temperatures provide these services! The process is quite simple, and the rewards are great.

A green and white hummingbird with blurred wings sips nectar from a butterfly weed bloom, which is a cluster of small crown-shaped orange flowers.
Who wouldn’t want to look forward to hummingbirds at their blooming butterfly weed this spring? Photo credit: Tom Murray

Take care to select plants suitable to the environmental conditions they will be planted in – “the right plant, right place.” Do you have full sun, full shade, or something in between? What about soil? Is it dry, wet or average? Whatever you plant, adding native plants to your landscape is sure to please wildlife (and you!) In my yard, I have dry sandy soil, but both butterfly weed (Asclepias tuberosa) and wild bergamot (Monarda fistulosa) thrive, and are frequented by birds and insects. You may find this website useful for helping you decide what to plant:

The picture is centered on the purple, fringed flower of wild bergamot. In the center of the bergamot bloom is a black-and-orange pearl crescent butterfly with wings spread.
Wild bergamot is a wonderful native plant that can attract pollinators like this pearl crescent butterfly. Photo credit: Tom Murray.

Plastic Bag Seed Starting Technique

  1. You can use seed flats with at least 2.25” depth (good for root development), recycled containers, or small pots you may already have – just make sure any container used has drainage holes. Fill with moist potting soil and tamp down to make sure that each cell is full and will not settle significantly. 
  2. Dibble (with a pencil or small stick) one small hole (about 1/4″ deep) in the soil  of each cell and place 2-3 seeds in each shallow hole. Gently compress the surrounding soil to seal the hole.
  3. Gently water the seed flat and let it drain for at least 10 minutes. Then place the seed flat within a labeled resealable plastic bag and seal tightly
  4.  Keep the seed flat for the remainder of the winter within the sealed bag exposed to freezing outdoor temperatures. We recommend keeping the bags in the dark or in a shaded area during the winter in locations such as: an unheated shed, under a deck or porch, or just stacked in a relatively dark corner of a backyard.
  5. Once the soil outdoors has fully thawed (generally by early or mid-April), place the plastic bag with seed flat in a sunny area outdoors. Moisten the soil in the seed flat and reseal the plastic bag. Remoisten the soil weekly.
  6. Check every couple of days for emerging shoots. These species are relatively slow to emerge and likely won’t germinate until May.
Three milk jugs and several plastic takeout containers full of seeds sit clustered together under a crust of snow and ice in someone's backyard.
If you’re worried plastic bags won’t be sturdy enough, here are some other common outdoor containers for winter sowing under cover of snow. Photo credit: Wintersown via Wikimedia Commons. Used under a Creative Commons 4.0 License.

 After Your Seedlings Emerge

  1. Once you see any green shoots emerge from the soil, open the seal on the ziploc bag, water the seed flat, and leave the seed flat in the unsealed bag for one more week.
  2. After one week, remove the seed flat from the plastic bag and keep it in a sunny area outdoors. Water once or twice weekly and fertilize with your favorite perennial fertilizer mix about once every 2 weeks. Remember to water regularly as small seedlings will die quickly without water during hot periods.
  3. After the first true leaves emerge, thin out the seedlings, if needed. (If you planted 2 or 3 seeds per hole, be ruthless and reduce to 1 individual per container. Use fine scissors to cut the stalks of the undesired seedlings. If you try to pull them out, you risk pulling all the small seedlings up. (Note: If you have the space and patience, you are welcome to try to transplant the extra seedlings into new containers.)
  4. When the seedlings are about 3” tall, they should be transplanted to 5” pots filled with potting soil or a potting soil and perlite mixture. 

Longer Term Care of Seedlings

  1. Water them regularly (twice weekly during the hotter months, once weekly will suffice in Spring and Autumn) and fertilize lightly about every two weeks. Depending on what you select to plant, you may do a fall planting. Otherwise, some plants may be overwintered: we recommend covering the pots with several inches of light mulch (e.g. shredded leaves, straw, shredded bark) and keeping them outdoors in a relatively sheltered location or in a cold frame or the pots can be sunk into the ground and mulched. Note: It’s best to stop fertilizing the plants in September to give them a chance to prepare for winter.