How to Winter Sow in Milk Jugs
Winter sowing starts seed outdoors in milk jugs in winter. Step by step: cut, drain, fill, sow, tape, label, and set outside, plus watering, venting, and...
Published by ThriveThyme
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How to Winter Sow in Milk Jugs
Winter sowing means sowing seed in covered containers, usually milk jugs, and leaving them outdoors through winter. The jug works like a mini greenhouse. Seed sprouts when the weather is right, and seedlings grow up already hardened off. No lights, no heat mat, no indoor space.
Get your sow dates on the Winter Sowing Desk. It counts back from your last spring frost.
What You Need
- Clear or cloudy plastic jugs: milk, water, or 2-liter bottles. Opaque jugs block too much light.
- Seed-starting mix or potting mix. Do not use garden soil. It can carry disease and weed seed.
- Duct tape, a knife or scissors, and a nail or drill for holes.
- A paint pen or grease pencil. Regular permanent marker fades in sun and rain.
Steps
- Wash the jug in warm, soapy water and rinse. Throw away the cap.
- Cut around the middle of the jug, leaving a 1 to 2 inch hinge under the handle.
- Punch 4 to 6 drainage holes in the bottom. Without them, seed drowns.
- Fill the bottom with 3 to 4 inches of mix. Wet it and let it drain.
- Sow at the depth on the packet. Press seed that needs light onto the surface. Pat the mix so seed makes contact.
- Close the jug and tape the cut edge. Leave the top open so rain and snow get in.
- Label the outside with the crop and date. Put a second label inside.
- Set jugs outside where they get winter sun, rain, and snow, out of strong wind. A milk crate or bin keeps them upright. Do not put them under a porch roof.
Care Until Spring
- Leave them alone in deep cold. Frozen jugs are fine.
- In warm, dry spells, check the mix. If it looks pale and dry, water from the bottom or mist through the top.
- Once seedlings are up, open the lid on sunny days and close it at dusk. A closed jug heats up fast in sun.
- When nights stay above freezing for hardy crops, or after last frost for tender crops, take the top off.
Transplanting
Plant out when seedlings are 2 to 3 inches tall with true leaves. Jug seedlings grow outdoors, so they do not need a long harden-off like indoor starts. Plant small clumps and thin, or tease seedlings apart. Tender crops such as tomatoes wait until after last frost.
Common Mistakes
- No drainage holes. Seed rots.
- Sowing tomatoes in January. Tender crops go last, about 6 to 3 weeks before last frost.
- Starting jugs in fall. A warm spell can sprout seed too early. Start in December or later.
- Leaving lids closed on sunny spring days. Seedlings cook.
See when to start winter sowing by zone and what to winter sow by zone. Plan your jugs on the Winter Sowing Desk.
Sources: Penn State Extension, Starting Seeds in Winter; University of Missouri Extension, Turn milk jugs into mini-greenhouses.