Winter sowing means sowing seeds in small, covered containers such as milk jugs and leaving them outdoors through the cold months. Snow, rain and freeze-thaw cycles do the work that you would otherwise do indoors under lights, and the seedlings sprout on their own when spring warms up. All you need are recycled containers, potting mix, seeds and a sunny spot outside.
Winter sowing: the short answer
Winter sowing works best for seeds that need a cold period before they germinate, such as many native perennials and wildflowers, and for hardy annuals and cool-season vegetables. Extension services such as Penn State, the University of Minnesota and South Dakota State describe the same basic method: clean a translucent container, add drainage holes, fill it with 2 to 4 inches of moist seed starting mix, sow, close the container but leave the top open for air and moisture, label it and put it outside in winter sun. Perennials usually go out from December to February, hardy annuals from January to March, and tender plants like tomatoes only in March or April. The exact timing depends on your USDA zone and your last frost date.
- Why winter sowing works
- Winter sowing containers compared
- Best seeds for winter sowing
- When to winter sow by USDA zone
- How to winter sow in milk jugs
- Using a grow tunnel as a mini greenhouse
- Caring for winter sown containers
- Hardening off and planting out
- Choosing the right setup for your garden
- Limits and common mistakes
- Winter sowing checklist
- Grow tunnel and raised bed for winter sown seedlings
- FAQ
Winter sowing step by step
Setting up a winter sowing container takes about ten minutes. After that, the containers mostly look after themselves until spring. The guide below covers the method, the best containers, which seeds to choose, a rough schedule by USDA zone and how to move your seedlings into the garden without losing them to a late frost.
Why winter sowing works
Winter sowing works because many seeds are built to spend the winter outdoors. In nature, they fall to the ground in fall, get wet and frozen over and over, and only sprout once the soil warms. This cold, moist period is called cold stratification. It breaks the seed's dormancy, so the seed knows winter is over.
A closed container acts as a tiny greenhouse. It protects the seeds from birds, mice and heavy rain, while snow and rain still reach the soil through the open top. On sunny days, it warms up a little more than the open ground, so seeds germinate somewhat earlier than if they were sown directly in the bed.
- No indoor space needed: no grow lights, heat mats or shelves full of trays.
- Sturdy seedlings: plants grow up with real sun, wind and cold, so they rarely become leggy.
- Less work in spring: the seedlings harden off on their own and are used to outdoor weather.
- Low cost: milk jugs and salad containers are free, and one bag of seed starting mix fills many containers.
Seed packets and catalogs often give clues that a plant is suitable for winter sowing. Penn State Extension lists terms such as self-sows, hardy seeds, needs pre-chilling, requires stratification and sow outdoors in late fall or early spring while frosts may still occur.
Winter sowing containers compared
The best winter sowing containers are translucent, at least 3 to 4 inches deep and have room for drainage holes and a vent. Each option has pros and cons:
- Gallon milk jugs: the classic choice. They hold enough soil, let in light and can be cut open and closed again with tape. Downside: cutting takes a bit of time, and white jugs let in less light than clear ones.
- Clear salad or bakery containers with lids: good for small seeds and many varieties in little space. Downside: they are often shallow and dry out faster in spring.
- 2-liter soda bottles: clear and easy to cut, but narrow, so they hold only a few plants.
- Plastic storage bins: useful for larger amounts of one plant, such as lettuce. Downside: they need many drainage and vent holes and take up more room.
- Ziplock bags: sometimes used with small pots inside. Downside: they do not drain well, tear easily and can trap too much moisture.
- A grow tunnel over containers: a walk-over tunnel such as the Grow Tunnel Superdome can shelter many open containers at once in late winter and spring. Downside: under a cover, rain and snow do not reach the soil, so you have to check moisture yourself.
Best seeds for winter sowing
The best seeds for winter sowing are native perennials and wildflowers that need cold stratification, hardy annuals that self-sow and frost-tolerant vegetables and herbs. Tender summer plants can also be winter sown, but only late in the season.
- Native perennials and wildflowers: many natives need a cold period, for example milkweed and coneflowers. Seed packets sometimes show a code like C30, which means at least 30 days of cold stratification.
- Hardy annuals: plants that reseed in your garden, such as poppies, larkspur, bachelor's buttons and calendula.
- Cool-season vegetables: spinach, certain lettuce varieties, kale, broccoli and Brussels sprouts. Illinois Extension mentions kale, broccoli, spinach and Brussels sprouts as frost-tolerant choices.
- Herbs: self-sowing herbs such as dill, cilantro and fennel, according to South Dakota State University Extension.
- Alliums: onions, chives and other alliums from seed.
- Tender plants, late only: tomatoes, peppers, basil, zinnias and squash do not need a cold period and are damaged by frost. Sow them in March or April, depending on your area.
When in doubt, read the seed packet. Phrases like direct sow after danger of frost has passed mean a tender plant that should go out late. Phrases like sow in fall or winter or requires a cold period mean the seed can go out early.
When to winter sow by USDA zone
Winter sow perennials and natives first, from about December to February, then hardy annuals and cool-season vegetables, and tender plants last, in March or April. In warmer USDA zones, everything shifts a few weeks earlier, and in colder zones a few weeks later.
The table below is a rough guide based on the extension recommendations above. It does not replace your local last frost date, which you can look up through your county extension office.
| USDA zone | Perennials and natives | Hardy annuals, cool-season crops | Tender plants |
|---|---|---|---|
| 3 to 5 | December to February | February to March | April |
| 6 to 7 | December to February | January to March | March to April |
| 8 | December to January | January to February | March |
| 9 and warmer | December to January, if nights stay cold enough | January to February | February to March |
Do not start too early. Illinois Extension recommends waiting until January or February in its region, because a warm spell can make seeds sprout and the young seedlings may not survive the next freeze. Perennials that need a long cold period are the exception and can go out earlier.
In mild climates, seeds that need a long cold period may not get enough chill outdoors. If your winters rarely freeze, start with hardy annuals and cool-season vegetables and treat natives as an experiment.
How to winter sow in milk jugs
To winter sow in milk jugs, cut the jug around the middle, make drainage holes, add moist seed starting mix, sow, tape it shut, label it and put it outside with the cap off. The steps below follow the method described by Penn State and the University of Minnesota Extension.
- Clean the jug: wash it in warm, soapy water and rinse it well.
- Cut it open: cut horizontally around the jug about 4 to 5 inches from the bottom, leaving a hinge of about 1.5 inches under the handle.
- Make holes: poke several drainage holes in the bottom. Without them, the seeds drown. Throw away the cap so air and moisture can get in through the top.
- Add potting mix: fill the bottom with 2 to 4 inches of seed starting mix or potting mix. Do not use garden soil, which can contain weed seeds and diseases.
- Water: moisten the mix and let excess water drain away.
- Sow: sow the seeds as the packet says and cover them lightly. Very small seeds that need light are only pressed onto the surface.
- Close and label: tape the cut shut. Write the plant name and date on the jug and on a label inside, because outdoor markers fade.
- Put it outside: place the jug in a spot with winter sun, not on a covered porch, because it needs rain and snow. In windy spots, set jugs in a crate or close together.
After that, leave the jug alone. The seeds will sprout when the weather is right, often in early spring for cool-season plants and later for natives.
Using a grow tunnel as a mini greenhouse for winter sowing
A grow tunnel can serve as a large mini greenhouse for winter sowing, especially in late winter and spring. It is not a replacement for the jugs in midwinter, because seeds that need cold stratification should get the full weather.
The Grow Tunnel Superdome is a transparent tunnel about 9.8 ft long (80 x 70 x 300 cm) with two openings on the side. It is useful in three situations:
- Late sowings: containers with tender plants sown in March or April get extra shelter from cold nights.
- Many containers in one place: the tunnel protects a group of opened jugs from heavy rain, hail and animals once the seedlings are up.
- Direct sowing in the bed: cool-season vegetables can be sown directly in the soil under the tunnel in early spring.
Two points matter: under a cover, the containers no longer get rain or snow, so check the moisture every few days. And a closed tunnel warms up fast on sunny days. Open the side openings in the morning and close them in the evening when frost is forecast.
Caring for winter sown containers
Winter sown containers need almost no care until the seeds sprout. Once the weather warms, check them regularly.
- Moisture: when the temperature stays above freezing, look at the soil every few days. If it is dry, water gently from above with a spray bottle or watering can.
- Snow: snow on top of the jugs is fine. It melts slowly and waters the soil.
- Ventilation: condensation inside is normal. On sunny spring days, the inside can get too hot, so open the jugs for a few hours.
- Patience: some native seeds take a long time to sprout. South Dakota State University Extension notes that some natives may not germinate until May or June or even later.
Hardening off and planting out
Winter sown seedlings harden off almost on their own. After they sprout, open the containers on sunny days and close them at dusk when nights are cold, as Illinois Extension recommends. As the nights get milder, leave them open longer, and finally remove the tops completely.
- Open in steps: first only during sunny afternoons, then for whole days, then also at night once frost is over.
- Wait for the right time: hardy plants can go into the garden once they have a few true leaves and the soil can be worked. Tender plants like tomatoes only go out after your last frost date.
- Plant in clumps: cut the side of the container open and slide the soil out in one piece. Divide it into small clumps rather than separating every seedling.
- Water in: water the transplants well and protect them from strong sun for the first few days.
A raised bed is a convenient place to plant winter sown seedlings because the soil warms up earlier in spring. The Raised Garden Bed CITY JUNGLE has a built-in water reservoir and a trellis, so climbing plants like peas or flowers like sweet peas can grow up right away. For cold nights after planting out, the matching Winter Cover CITY JUNGLE made of transparent bubble wrap covers the bed. More ways to protect young plants from frost can be found in our guide How to Protect Plants from Frost.
Choosing the right setup for your garden
Which setup is right depends on how much you want to sow and where.
- A few varieties, little space: a handful of milk jugs on a sunny balcony or patio is enough.
- Many flowers or natives: collect containers in fall and set them close together in a protected spot that still gets rain and snow.
- Vegetables for the garden: combine jugs for early sowings with a grow tunnel over the bed for late sowings and the first transplants.
- Patio or small garden: a raised bed with a cover gives seedlings a warm, protected start after planting out. To get your beds ready for this, see our guide to winterize raised garden beds.
Limits and common mistakes
Winter sowing is simple, but it is not always faster. If spring is long and cold, many winter sown plants only sprout in May or June, so indoor seedlings can be ready for planting earlier. These are the most common mistakes:
- No drainage holes: water collects at the bottom and the seeds rot.
- Cap left on: without an opening, no moisture gets in, and on sunny days the jug overheats.
- Covered location: containers under a roof or porch dry out and miss the cold, moist weather.
- Tender plants sown too early: tomatoes or zinnias that sprout during a warm spell in February often die in the next frost.
- Garden soil: it compacts in containers and brings weed seeds and diseases.
- Missing labels: marker on the outside fades in the sun. Always add a label inside.
- Forgetting to water in spring: once temperatures rise, containers dry out quickly.
Winter sowing checklist
- Collect translucent containers at least 3 to 4 inches deep.
- Wash containers in warm, soapy water.
- Cut milk jugs around the middle and leave a hinge.
- Poke drainage holes in the bottom and remove the cap.
- Fill with 2 to 4 inches of moist seed starting mix.
- Sow as the seed packet says and cover lightly.
- Tape the container shut and label it inside and outside.
- Place it in winter sun, not under a roof.
- Sow perennials and natives first, tender plants last.
- Check moisture as soon as temperatures stay above freezing.
- Open containers on sunny days once seedlings appear.
- Plant out in clumps; tender plants only after the last frost.
Grow tunnel and raised bed for winter sown seedlings
FAQ
Does winter sowing really work?
Yes, winter sowing works well for seeds that tolerate or need cold, such as many native perennials, hardy annuals and cool-season vegetables. Several university extension services recommend it. It works less reliably for tender plants sown too early and in regions where winters are too mild for cold stratification.
Can you winter sow tomatoes?
Yes, but not in midwinter. Tomatoes need warmth to germinate and are damaged by frost, so sow them in March or April, depending on your zone. Winter sown tomatoes often sprout later than indoor seedlings, but they grow into sturdy plants. Plant them out only after your last frost date.
Do you water winter sowing containers?
Usually not in winter, because rain and snow get in through the open top. Once temperatures stay above freezing, check the soil every few days and water gently if the surface is dry. Containers under a grow tunnel or roof always need to be watered by hand.
How many seeds go into one milk jug?
That depends on the plant. For flowers and lettuce, many gardeners sow quite densely and later plant out small clumps. For larger plants like tomatoes or squash, a few seeds per jug are enough. Follow the spacing on the seed packet as a guide.
Winter sowing turns empty milk jugs into a free seed starting station. Sow cold-hardy seeds in winter, tender ones in spring, check moisture once it gets warmer, and your seedlings will be strong and ready for the garden when the season starts. A grow tunnel and a raised bed with a cover help your young plants through the last cold nights.