Winter sowing is a lazy, cheap way to start native seeds outdoors: you plant them in clear milk jugs, set the jugs outside in winter, and let Maryland's cold do the hard part. In Maryland, aim to sow between December and February, then move seedlings into the garden after the last frost, which usually lands around April 10.
Why winter sowing works
Many native wildflowers will not sprout until they have been through a cold, damp winter. Gardeners call this cold moist stratification. It is a fancy name for "the seed needs to sit in cold, wet soil for a while before it believes spring is real." It is a built-in safety switch, so seeds don't sprout during a warm spell in October and then freeze.
You can fake stratification in the fridge with damp paper towels. Winter sowing skips that fuss. The milk jug acts like a tiny greenhouse. It keeps seeds moist and protected, lets in rain and snow, and exposes them to real freeze and thaw cycles. When spring warms up, the seeds sprout on their own schedule, already used to outdoor conditions. That means no grow lights and less "hardening off," which is the slow process of getting indoor seedlings used to sun and wind.
As a new gardener, I find this approach very appealing. It is basically gardening on autopilot.
What you need
- Clean, clear or translucent plastic gallon jugs (milk or water jugs work best)
- A sharp utility knife or scissors
- Something to poke holes: a drill, a heated skewer, or a screwdriver
- Seed-starting mix or a light potting mix (not heavy garden soil)
- Native seeds that need cold stratification
- Duct tape or packing tape
- A paint pen or permanent marker, plus a plant label for inside the jug
Step-by-step: how to winter sow in milk jugs
1. Cut the jug into a hinged "clamshell"
Rinse the jug. Cut around it horizontally about 4 to 5 inches up from the bottom, but stop before you go all the way around. Leave a strip of an inch or two uncut, right under the handle. That strip is your hinge, so the top flips open like a lid.
2. Add drainage holes
Poke 4 to 6 holes in the bottom so water can drain. Soggy soil rots seeds.
3. Fill with 3 to 4 inches of moist mix
Pre-moisten your seed-starting mix until it feels like a wrung-out sponge. Fill the bottom of the jug with 3 to 4 inches of it and press it down lightly.
4. Sow at the right depth
This is where beginners (me included) get tripped up. A simple rule: tiny seeds go on the surface, larger seeds get a light cover.
- Dust-like seeds, such as those of Cardinal flower or Great blue lobelia, should be scattered on top and gently pressed in. Many of them need light to germinate.
- Medium and larger seeds, like coneflowers or milkweeds, get covered with roughly their own thickness of mix. A thin sprinkle is plenty.
Don't overthink spacing. Crowded seedlings can be teased apart later.
5. Label it twice
Write the plant name and date on the outside of the jug with a paint pen. Sunlight fades regular markers by spring, so tuck a second label inside too. Future you will be grateful.
6. Tape it shut and leave the cap off
Close the lid and tape around the cut seam. Leave the cap off. The open spout lets rain and snow in and lets heat out on sunny days.
7. Put the jugs outside
Set them somewhere that gets sun and rain, like a patio, deck, or a spot along a fence. Avoid places under a roof overhang where precipitation can't reach. Grouping jugs together in a tote or crate helps keep them from blowing over.
When to winter sow in Maryland
Maryland's average first frost is around October 31, and the average last frost is around April 10, based on NOAA 1991-2020 normals. Frost dates vary by location, roughly March 29 to April 29 for the last frost depending on where you live. You can check details on the Maryland sowing calendar.
| Window | What to do |
|---|---|
| Nov (after first frost) | Gather jugs and mix. Early sowing is fine for very hardy seeds. |
| Dec to Feb | Ideal sowing window for most natives that need cold stratification. |
| Early Mar (to about Mar 11) | Last call for stratification-loving seeds. |
| Mar to Apr | Watch for sprouts. Open lids on warm days. |
| After about Apr 10 | Transplant seedlings with true leaves into the garden. |
The sweet spot is December through February. That gives seeds several weeks of cold, wet conditions before spring. If you sow too early, during a warm fall stretch, some seeds may sprout and then get zapped by frost.
Good native seeds to winter sow
These Maryland natives are commonly winter sown because they benefit from a cold, moist period:
- Butterflyweed: bright orange flowers May to September, 1 to 2 feet tall, full sun, and a larval host for Monarch butterflies.
- Swamp milkweed: pink flowers June to October, up to 5 feet, likes wet soil. Also a Monarch host plant.
- Eastern purple coneflower: up to 4 feet, sun to part shade, a classic for butterflies and bees.
- Pale purple coneflower: a slimmer cousin with drooping petals, blooms May to July in full sun.
- New England aster: purple flowers from August until frost, and a larval host for the Pearl Crescent butterfly.
- Dense blazing star: tall purple spikes July to September, loved by butterflies and native bees.
- Eastern red columbine: red and yellow nodding flowers for hummingbirds, happiest in part shade.
- Foxglove beardtongue: white tubular flowers May to July, a favorite of bumblebees.
- Cardinal flower: brilliant red spikes for hummingbirds, likes moist to wet soil. Surface sow.
- Great blue lobelia: blue flowers July to October in moist spots. Surface sow.
Tip for milkweed lovers: both milkweeds above feed Monarch caterpillars, so a few jugs of each go a long way. For more ideas, browse Maryland butterfly host plants or the wider list of Maryland plants for pollinators.
Caring for your jugs over winter
Winter sowing is mostly hands-off, but not completely.
Check moisture now and then. Rain and snow usually do the job. During a dry spell, peek inside. If the mix looks pale and dry, water gently from the top or set the jug in a tray of water to soak up from below.
Don't panic about freezing. Snow on top, frozen soil, ice in the jug: all normal. That is the stratification happening.
Spring: sprouts, venting and transplanting
As days warm in March and April, sprouts will start popping up. Different species wake up at different times, so don't toss a jug just because it is slow.
Open the lids on warm days. On sunny days above roughly 50 degrees, the jugs can overheat quickly. Untape the seam and flip the lid open during the day. Close it again on cold nights when frost is in the forecast. By late spring you can remove the tops completely.
Wait for true leaves. The first pair of leaves a seedling shows are "seed leaves" (cotyledons). They often look nothing like the adult plant. The next leaves to appear are the "true leaves," which look like small versions of the real thing. Once seedlings have a set or two of true leaves and the last frost has passed, around April 10 in much of Maryland, they are ready to move.
Transplant in clumps. Many gardeners cut the soil into small squares, like brownies, and plant each clump. You can thin to the strongest seedling later. Water well after planting and keep the soil moist for the first couple of weeks.
A few beginner mistakes to avoid
- Using garden soil. It packs down and drains poorly. Stick to seed-starting mix.
- Forgetting drainage holes. Seeds sitting in water will rot.
- Leaving the cap on. No rain gets in, and the jug can cook on a sunny day.
- Skipping labels. Many native seedlings look alike when small.
Your winter sowing game plan
Save a handful of jugs over the next few weeks. Pick three to five natives from the list, sow them sometime between December and February, tape them up, and set them outside. Check them occasionally, vent them on warm spring days, and plant out after mid-April. If you want more plants to try, the plant finder and the Maryland state page are good next stops.
I'm trying this myself this winter and will add photos as the jugs sprout.