Most of the wildflowers in the Missouri Native Series won’t sprout until they’ve spent weeks cold and moist. On the prairie, that happens on its own: seed drops in fall, sits through winter, and comes up in spring. Winter sowing copies that. You sow outdoors between December and February, in containers or on bare ground, and the weather does the rest.
No grow lights. No fridge space. Just a little prep on a winter afternoon.
Why it works
Many native seeds carry a built-in dormancy that a cold, moist spell breaks. Seed growers call the treatment cold-moist stratification, and Prairie Moon Nursery marks those seeds with a “C” code: C(30) needs about 30 days, C(60) about 60. Sow them outdoors in winter and they get their days without you counting.
Seeds that don’t need a chill, like Purple Coneflower and Wild Bergamot, winter-sow just as well. They simply wait for spring.
Which numbers to winter-sow
| No. | Species | Prairie Moon code | Winter sowing |
|---|---|---|---|
| 1 | Purple Coneflower | A | Works well; a winter outdoors evens out germination |
| 2 | Ozark Coneflower | C(60) | Yes. Sow early in the window |
| 3 | Black-eyed Susan | C(30) | Yes. Press tiny seed onto the surface |
| 4 | Butterfly Milkweed | C(30) | Yes. Use a deep container or sow where it will grow |
| 5 | Swamp Milkweed | C(30) | Yes |
| 6 | Common Milkweed | C(30) | Yes. No more than 1/4 in deep |
| 7 | Wild Bergamot | A | Works, though spring sowing is just as easy |
| 8 | Lanceleaf Coreopsis | C(30) | Yes. Light helps it germinate: don’t cover |
| 9 | Rough Blazing Star | C(60) | Yes. Sow early in the window |
| 10 | New England Aster | C(60) | Yes. Press tiny seed onto the surface |
| 11 | Missouri Evening Primrose | C(60)* | Yes, though fall is its postmark |
| 12 | Golden Alexanders | C(60), G, M | Yes. Fall or early winter is best |
*Sources differ on No. 11: the Lady Bird Johnson Wildflower Center says it needs no treatment. Winter sowing suits it either way.
When to sow in St. Charles County
- December through February is the window. Many gardeners start around the winter solstice (University of Illinois Extension).
- 60-day seeds (Nos. 2, 9, 10, 11 and 12) should be outdoors by mid-February. St. Charles County’s median last spring freeze is around April 10 (National Weather Service, 1991–2020), so mid-February gives them about 60 cold days.
- 30-day seeds (Nos. 3, 4, 5, 6 and 8) can go out any time through the end of February.
- Earlier is fine. Seed with a cold requirement stays dormant until it’s had its chill, so a late-fall sowing works too.
Method 1: Containers (the milk-jug method)
You’ll need: clear or translucent gallon jugs (milk, water or juice jugs, washed), potting mix, duct tape, a sharp knife or drill, a marker and plant labels.
- Cut the jug. Remove the cap. Cut around the jug about 6 inches up from the bottom, three-quarters of the way, so the handle side becomes a hinge.
- Add drainage. Make six or seven holes about 1/4 inch wide in the bottom.
- Fill. Add 3–4 inches of pre-moistened potting mix, tamp it lightly, and water until it drains.
- Sow one species per jug. Space the seeds out. Tiny seeds (Nos. 3, 7, 8 and 10) get pressed onto the surface, not buried. Others get a light covering, about 1/8 inch, or as the packet says. A good rule: no deeper than the width of the seed.
- Water gently to settle the seed. Use a sprinkle, not a stream, for small seeds.
- Label inside and out. Put a label inside with the name, date and number of chill days, and write the same on the outside. Marker fades over a winter; the inside label is your backup.
- Tape it shut with duct tape.
- Set it outside where rain and snow can reach it but it won’t blow away, out from under the eaves. A protected spot keeps animals out.
- Leave it. Check now and then during dry spells; if the mix is dry, water lightly.
Method 2: Bare ground (direct sowing)
This is the way the prairie does it, and it’s the simplest choice for larger areas.
- Clear a spot to bare soil. Pull weeds and rake away mulch. Prairie Moon recommends a bare, weed-free, firm site.
- Scatter the seed and press it in so it touches the soil. Leave tiny seeds on the surface.
- Mark the area with plant markers. In spring, native seedlings are easy to mistake for weeds.
- Let winter work. Snow, rain and freeze-thaw settle the seed in.
Spring care
- Open the jugs on warm days once sprouts appear. Remove the tape, fold the top back on its hinge and weigh it down. Close it on cold nights.
- Keep the mix moist. Seedlings dry out faster once the lid is open.
- Transplant at one or two sets of true leaves (not counting the first seed leaves). Tease seedlings apart gently, or cut the soil into chunks like brownies and plant each chunk.
- Harden them off. Give seedlings a gradual week of more sun and wind before planting them out.
- Plant after the last frost. That’s around April 10 in St. Charles County and April 2 at St. Louis Lambert airport (National Weather Service medians).
- Water the first summer. New roots need help during dry spells.
When to expect sprouts
These are typical times for the St. Louis area. Weather varies from year to year, and native seed doesn’t always come up all at once.
| Numbers | Winter-sown seed usually sprouts |
|---|---|
| 12 Golden Alexanders | March–April (it likes cool soil) |
| 1, 2, 3, 8, 9, 10, 11 | March–May, as the soil warms |
| 4, 5, 6 (the milkweeds) | April–May, once the weather warms |
| 7 Wild Bergamot | Spring, once the soil is warm (it needs no chill) |
Sowing in spring instead, after a fridge chill? Expect seedlings within about four weeks in warm, moist soil. Black-eyed Susan is often up in one to two weeks.
If nothing comes up
Give it time. Some native seed takes a second spring to germinate, so leave the jug or patch undisturbed for another year. Prairie Moon’s advice: “If seed does not germinate the first year, don’t give up.”
If a packet doesn’t come up after you follow this guide, our Grow Guarantee covers a replacement packet within 12 months.
What to expect after that
Native perennials spend their first year growing roots. Gardeners call it “sleep, creep, leap”: year one is mostly roots, year two brings more growth and some flowers, and by year three plants reach full size (Purdue Landscape Report). Black-eyed Susan is the exception that often blooms the first summer.
Sources: Prairie Moon Nursery, germination codes and instructions; University of Wisconsin–Madison Division of Extension, Dane County, “Winter Sowing Native Wildflower Seed” (Jan. 7, 2026); University of Illinois Extension, “How to try winter sowing” (Jan. 15, 2024); National Weather Service St. Louis, frost/freeze normals 1991–2020; Lady Bird Johnson Wildflower Center (Oenothera macrocarpa); Purdue Landscape Report, “Sleep, Creep, Leap” (May 1, 2026). Full links in our sources list.