Winter sowing is a seed starting method that makes use of outdoor conditions (cold weather and sunshine) to germinate seeds when it’s freezing outside. Grab old milk jugs or other containers to act like mini greenhouses and let’s get started.
If you would rather sow indoors, see Seed Starting for Beginners for my best tips. This outdoor sowing method is ideal for native seeds in cold climates.
Winter Sowing: Starting Seeds Outdoors
When you first learn about winter sowing it seems a bit mysterious. How can seeds germinate out in the cold—don’t they need warmth and moisture to sprout?
Yes, they do. And, with some household supplies and winter sun, winter sowing can provide just what’s needed.
While we can grow just about any annual or perennial seeds this way—other than tender tropical plants—this method is particularly valuable for sowing native and other seeds that require a cold chill—”stratification”—to trigger germination.
How Winter Sowing Works
We call it ‘winter sowing’ but instead of sowing the seeds directly outdoors we’re sowing in clear, closed but ventilated containers like milk jugs which act like mini greenhouses.
With seeds sown (you can do that part indoors), the closed containers are placed outdoors to experience winter conditions—cold, snow, rain, you name it.
The seeds remain dormant while chilling, and, as spring approaches, light and heat increase and germination is triggered.
I’ll walk you through all the basic steps including recommended supplies and seed choices.
Be sure to grab the ebook if you’d like everything in one handy file.
Getting Started With Winter Sowing
Winter sowing is intended for cold climate gardeners who get freezing or near-freezing temperatures for several months of the year.
See the Resources section for links to look up your hardiness zone and last frost date.
- Prepare Milk Jugs
- Potting Mix
- Sow Seeds
- Tag and Seal Jugs
- Place Outside
- Ongoing Care Outdoors
- Thin Out, Grow On, Or Transplant
Winter sowing can take place from winter to spring, up until a few weeks before last frost.
It’s helpful to organize your winter sowing into three main groups based on when the seeds can be started. There is a lot of overlap between Groups A and B.
This is an overview. The Winter Sowing Seed List section below has lots of recommendations.
A) Early Winter Sowing
5 to 6 Months Before Last Frost
Sow seeds needing weeks or months of stratification.
This group includes many flowering perennials and cold-tolerant vegetables in addition to native plants, trees, shrubs, and vines.
For me in zone 6, sowing time is December and January.
Examples: delphinium, milkweed, lupine, columbine, clematis.
B) Winter Sowing
3 to 4 Months Before Last Frost
Sow cold-hardy perennials or annuals.
For me in zone 6, sowing time is February and early March.
Examples: Brussels sprouts, Monarda (bee balm), pansies.
This group also includes vegetables we can grow in winter (with some protection).
C) Late Winter / Early Spring Sowing
1 to 2 Months Before Last Frost
This group includes tender annuals including flowers and vegetables that do not require stratification and need consistent warmth.
Here in zone 6, sowing time using the winter sow method is late March and April.
Examples: cosmos, zinnia, tomato, eggplant.
The example I’ve used for this article is 2-gallon milk jugs but you can use just about anything that fits the criteria. Check your recycling bin or ask friends for what you need.
Whatever combination you choose, be sure:
- Light can reach the future seedlings.
- The materials can withstand winter weather.
- There is adequate room for root growth as well as the future height of the plants.
- The planting container accommodates a good volume of potting mix to reduce the chance of drying out.
- You can make drainage holes in the base and ventilation holes up top (more on this below).
- You will be able to easily access your plants when it’s time to transplant.
There’s two basic options:
- Grow the seeds in an all-in-one container like a plastic milk jug, or
- Grow the seeds in individual pots and sit them in a larger, clear or translucent bins with lids or large ziplock food bags.
Whatever you choose, you must have drainage holes.
These are just a few possibilities. See what you have that fits the criteria and try it.
- Milk, juice, or water jugs
- Large soda pop or beverage bottles
- Cat litter jugs
- Clear clamshells / food containers (double them up if they have too many vent holes)
- Clear ice-cream or other food tubs (with lids)
Containers Within Bins or Bags
You can also sow in more traditional containers and place them within bins or Plastic ziplock food bags with drainage holes.
- Plastic beer cups or Solo cups
- 4-inch or larger plastic flower pots
Clay pots are not recommended because they absorb moisture and may crack in the cold.
Where to Get Containers
The beauty of winter sowing is how it makes use of containers headed for landfill.
To find containers,
- Check your garbage and recycling.
- Ask friends and neighbors for theirs.
- Enquire at local restaurants—many use large volumes of products that come in plastic jugs perfect for winter sowing.
Also hang onto plastic food bags—you can get a lot of use out of them before the wear out.
How to Clean Containers
Wash everything in soapy water, rinse thoroughly, and then disinfect with a bleach solution (4 teaspoons bleach per quart or liter of water for at least one minute).
Containers used for winter sowing may last just one season depending on how brittle the plastic becomes under outdoor conditions. Sturdier tubs may endure many seasons of use.
3Prepare Milk Jugs
We cut across the middle of the milk jug to create a base where the potting mix goes while keeping a top to form a mini greenhouse.
You want to allow at least 4 to 6-inches of room for potting mix, root growth, and watering in the base of the jug.
These are 3 different ways to do this:
- Make a partial cut around the middle of the jug (but below the base of the handle), leaving a section that forms a hinge (as shown in diagram, above).
Draw a line where you want the cut, make pilot holes, and then cut, leaving a hinge
- Cut a little door in top half of the jug, leaving a top hinge and room to place potting mix inside. It should be big enough to fit your hand inside.
- Cut the jug into two sections (top and bottom) and cut vertical slits into the top lip of the base. This will allow the top of the jug to sit nicely over the base (no tape required).
Make Cuts and Holes
Wear safety glasses and gloves and always aim away from yourself while cutting.
Cuts and holes may be made with some combination of:
- Exacto knife
- Box cutter
- Serrated knife
Holes or Slits
- Wood burning tool
- Heated screwdriver tip
- Electric drill (see tips)
- Heated awl
- Hot glue dispenser (without glue)
- Soldering iron
- If you can, test out some methods first to see what’s easiest for you. For some, getting the cuts nice and straight is paramount while others don’t care.
- If you choose to burn the plastic to create holes, work outside in a well-ventilated area.
- It’s much easier to drill holes in the base from the inside of the container aiming onto a scrap piece of wood while the plastic is fully supported. Otherwise, if you drill from the underside into the empty jug, it’s more likely to crack.
- It can also help to run your drill in reverse while gently pressing down—this causes less pressure while still creating holes.
- You can also cut slits in the base. So long as the excess water can drain out, you’re good.
Use organic potting mix, not seed starting mix, which will dry out too quickly. You could also use soil from your garden if it’s up for the job—I don’t use mine because it’s way too sandy.
I look for a potting mix deemed safe for food crops (growing vegetables) so I don’t have to worry about where it ends up.
How much potting mix will I need?
It’s hard to name a specific amount because we’re using an assortment of containers and potting mix is sold by various units.
- 25 quarts of moistened potting mix should fill 15 1-gallon milk jugs at a depth of 4-inches each.
- 2 cubic feet of moistened potting mix should fill 30 1-gallon milk jugs at a depth of 4-inches each.
We do have a soil calculator here if you want to determine specific amounts based on your containers and how potting mix is sold where you are.
Also keep in mind that we’re moistening the potting mix which removes a lot of the air pockets so it won’t go as far as you’d think. It really sinks down once you add water. If you are eye-balling it, buy twice as much as you think you need. You can always use any surplus later.
Pre-moisten Potting Mix
Before adding potting mix to your jug, moisten it with water. It should be moist enough to form a ball when you press it together but not so much that water drips out.
Some seeds like salad greens just form shallow roots while others (e.g. tomatoes) go deeper. A depth of at least 4-inches works for most plants for the seedling and young plant stages.
If your potting mix is too shallow, the plant roots could freeze early on or become rootbound later.
Seed Sowing Depth
Winter sowing is just like any other seed sowing: follow the instructions on your seed packet for things like sowing depth and whether the seeds should be covered. Most germinate in darkness but there are some that need light to sprout.
This comes down to personal preference. Do you want to thin out or divide seedlings later or not? And how many plants do you want / need?
Thinning & Dividing | Some gardeners like to sow a lot of seeds and either thin them out later or use the H.O. S. or “hunk of seeds” approach. This is where seedlings—all clumped together—are gently teased apart into smaller groups for transplanting.
I have friends who sow thickly because they are growing high volumes for spring plant sales. This works if you are prepared for the next step—transplanting a zillion seedlings.
Sow Sparingly | When I know my seeds have good germination rates, I sow just what I need with a few extra for insurance because I do not like thinning seeds and I’m super frugal. Sowing a lot of seeds at once can add up!
Do what fits your situation: how many plants you hope to grow, how much room you have, and how much work you’re equipped to do.
One Seed Type Per Jug
Ideally we start just one type of seed in each milk jug otherwise it gets tricky with varying plant heights and needs as things grow.
An exception is something like leafy greens or mesclun mix where the different varieties grow nicely together in a compact space.
As mentioned in the Timing section, it’s helpful to start seeds in 3 different phases depending on how long of a stratification period they require (or not). This means starting batches of seeds in early winter, winter, and late winter / early spring depending on the seeds.
We stop using the winter sowing method each spring when outdoor conditions are right for direct outdoor sowing.
Want the Winter Sowing ebook? Grab it here.
6Tag and Seal Jugs
Tags & Labels
I’ll remember what I sowed! says every gardener who later forgets.
Be sure to keep track of what you’re growing.
There are lots of options for tagging your sowing jugs. Most of us do several things just in case.
Bonus points for labelling both the inside and outside of the container.
Use markers, tags, and tape or any combination of these.
- Paint marking pens or another UV-resistant marker, grease pen, or pencil all work. Regular Sharpie pens do not work: they fade in the sun. Markers need to be oil-based to work.
- Label the jug, write on the tape, and/or place a plastic plant tag inside the jug.
I record the type of seed, source (seed company), and date sown.
Another option is to assign a unique number to each jug and keep a separate, corresponding written record.
For more ideas, see these ways create plant tags or markers.
Seal the Jug
We need to close up the jug (or container) except for the top ventilation hole(s) so they can act like mini greenhouses, retaining heat from the sun without overheating.
Some gardeners forgo the ventilation holes or hold off adding them until warm spells in spring. I’ve found I need them sooner due to the intense winter sun where I am. You can always cover the ventilation holes with a clear bag until you need them.
To seal milk jugs shut, there are lots of options.
Tape | Duct tape, poly tape, Gorilla all-weather tape, or freezer tape.
Cons: Can be wasteful if you have to cut and/or remove it each time you need to open the jug.
Some gardeners also like masking tape or painter’s tape. The trick is to apply them at room temperature to get them to stick.
Ties | Other options include punching holes along the seam of the milk jug and tie the top and bottom together with twist ties, wire, pipe cleaners, or shoelaces. Or create hinges with zip ties.
Zippers | I’ve also used old zippers affixed to the jug using GE II Silicone sealant as adhesive. Look for bags of zippers at second hand shops.
Overlap | As mentioned earlier, you can also cut the jug in such a way that the top section overlaps the bottom by an inch or so, making it really easy to open and close.
Opting for other types of containers avoids the whole how-will-I-do-this? dilemma.
At last, the fun can happen.
Cold and light are key for winter sowing, particularly the early group requiring stratification when weather is coldest and days are short.
Place your jugs in a sunny location, away from buildings, avoiding any puddle-prone areas, out of direct wind (which can knock the jugs over or dry out the potting mix).
This could be on the ground or on a patio table.
Resist the urge to sit the jugs next to your house or cover them with straw. The point is to expose them to the elements, out in the open where snow can cover them.
You may also want to run twine or a long stick through the handles to hold the jugs together or sit everything in tubs with drainage holes for extra security. If your milk jugs blow over, it’s a hint the potting mix may be drying out—so check on that.
If you find the sun is too intense, obviously switch to part-shade.
Snow and rain are welcome. Snow provides insulation. I keep vent holes open the whole time so some rain can also sneak in.
You can adjust things as you go according to your unique conditions.
It’s up to you to monitor the jugs to ensure they don’t overheat or dry out: there’s more on this below.
I also like to briefly lift the containers each time I’m checking on them. Once in a while I find they are sticking to the ground which can block the drainage holes.
Winter Sowing Raised Bed
If you are winter sowing on a patio, this DIY tall raised bed is designed to fit two bins or a bunch of milk jugs. I’ve included building plans in case you want to make one.
The height makes it handy for checking your plants, especially if kneeling in snow is not your thing.
8Ongoing Care Outdoors
Water and Ventilation
Ongoing care involves ensuring the potting mix stays moist and the jugs do not either overheat or succumb to unusually cold conditions once your seedlings have appeared.
For the early seeds that require stratification, if the weather stays below freezing, there won’t be anything to do.
It’s when we get warm spells (a few degrees above freezing or more) or wild weather that you’ll want to check on things.
The first thing you’ll notice is condensation inside the jug. This is good. It means there is moisture available and the jug is indeed behaving like a greenhouse.
On warm or intensely sunny days (even if it’s cold), check the temperature in the jug and whether the potting mix needs watering.
I like to use a no-contact thermometer like this one to measure the temperature inside the jug. If things are heating up, I have no problem opening the jug right up to cool things off for any cold hardy seeds.
However, spring-sown seeds like tomatoes and peppers do not like temperature swings so they require more care. I only open up the jug to vent them if the outside air temperature is within 10 degrees of the inside jug temperature. Or, I bring them indoors for any maintenance.
Late Cold Spells
The other wildcard is unusual spring cold snaps. There is a progression as the seeds sprout and the young seedlings start to grow their mature leaves. Tolerance for cold and temperature swings varies by species.
If a rogue spring storm or freeze is coming, I cover the jugs of tender seedlings until the risk is over. You can use old blankets, tarps, straw, or place the jugs in bins in a sheltered location. Just remember to uncover them when the freeze is over.
As mentioned, never let the potting mix dry out.
You can water the jugs by sprinkling water in the open top (only while the seedling roots are still shallow) or sitting the jugs in a tray of water, letting the potting mix take up the water through the bottom drain holes for approximately 30 minutes or until adequate moisture is obtained. Or remove the tape and water that way, using a gooseneck watering can to reach the potting mix with the spout. .
I am a lifelong moisture meter user but your finger tip (down to a knuckle) can also tell you how moist soil is.
Most seeds in winter sowing conditions take approximately 6 to 8 weeks to germinate—unless they’re in a deep freeze which pauses everything.
It’s always fun to check on the jugs and see tiny green shoots appearing inside!
Some seeds are total slow pokes so be patient. I’ve had delphiniums, milkweeds, and columbines all take their sweet time. The milkweeds in particular may not sprout until their second year—so check your seed packet info.
Also, tree seeds often require a double dormancy (two winters) before they sprout. In this case, one year in the fridge and winter sowing during year two could work.
Fertilizer is not required until there are a few sets of mature leaves on the plants. I hold off if it’s spring and almost time to direct sow them anyways.
9Thin Out, Grow On, or Transplant
As your seeds grow and the weather warms, it’s time to allow more ventilation either by increasing the number of vent holes, opening the jugs up each day, or removing bin lids.
Depending on conditions, you may need to close them each evening as the sun goes down and open them up again mid-morning each day.
This process is called hardening off: getting plants used to natural outdoor growing conditions.
Thinning out is generally done when a seedling has at least two sets of mature leaves. The idea is to remove all but the best growers.
If your seedlings are getting crowded and it’s too soon to plant them out, you may need to transplant them to larger pots which can remain outdoors in bins (with lids ready in case it gets cold).
Use the instructions on your seed packets to know when transplanting is recommended. This is usually after the risk of frost has passed but there’s always some exceptions.
Sheila followed the tips in this article and wrote to share her winter sowing results. Living in hardiness zone 4 in Minnesota, her summer growing season is fairly short.
The seeds were started in milk jugs in February. Sheila mentioned duct tape worked better than packing tape.
It snowed a lot after sowing so the jugs were snow-covered much of the time and didn’t require maintenance. In milder climates like mine, we toggle so much between freezes and thaws that I have to monitor my own winter sowing containers a few times a week or risk things overheating or drying out. But colder climates have their perks!
Sheila said she just watered once. The results you see here are from mid-May (3 months after sowing).
That’s a wonderful assortment of plants!
Winter Sowing Seed List
Seeds suitable for this method can be divided into three main sowing groups based on when you sow.
As with all planting, be sure that your seed choices are non-invasive in your area and suitable for your growing conditions.
There are thousands of plants I could list. I have opted to be sensible and stick to some popular examples.
A) Early Winter Sowing
5 to 6 Months Before Last Frost
Seeds needing weeks or months of stratification.
For me in zone 6, this is December and January.
This includes many flowering perennials in addition to native plants, trees, shrubs, and vines. Some vegetables like broccoli and Brussels sprouts can also handle an early start.
Milkweed (Asciepias spp.) are perfect for this type of sowing.
If your seed packet recommends months of cold stratification, include the seeds in this group.
B) Winter Sowing
3 to 4 Months Before Last Frost
Seeds needing moderate periods of stratification and / or hardy perennials and annuals.
For me in zone 6, this is February and early March.
I’ve listed some possibilities below—there are hundreds more. Seed catalogs sometimes list suggestions by sowing time as well.
Be sure to pick seeds suited to your hardiness zone and growing conditions and avoid invasive species.
- Bee balm (Monarda)
- Bell flowers (Campanula)
- Blazing star (Liatris)
- Clematis (Group A)
- Columbine (Group A)
- Coneflower (Echinacea)
- Delphinium (Group A)
- Foxglove (Digitalis)
- Joe Pye Weed
- Milkweed (Group A)
- Lupine (Group A)
- Rose campion
- Brussels sprouts
- Leafy greens
- Sweet Marjoram
C) Late Winter / Early Spring Sowing
1 to 2 Months Before Last Frost
Tender annuals including flowers and vegetables that do not require stratification and need consistent warmth.
Here in zone 6, this is late March and April.
Frequently Asked Questions
The winter sowing method using protected containers outdoors works for just about any annual or perennial seed with the exception of tropical seeds.
Winter sowing is very good for any cold hardy seeds that require ‘stratification‘—a period of cold chilling (weeks or months, depending on the species) that prepares certain seeds for germination.
By using containers, we’re basically mimicking what nature does but giving the seeds better odds by sheltering them from challenging conditions and critters that might eat them.
Many of our native plants require stratification and can be started this way. Favorites include delphinium, goldenrod, New England aster, milkweed, lupine, and columbine, along with various trees, shrubs, and vines.
Basically, if a plant grows in temperate or continental climates, not tropical or polar areas, it can be winter sown. I’ve provided an extensive sowing list below.
Yes, winter sowing works for a range of annuals and perennials—just about anything you would grow in your garden.
If the seeds require a cold chill (stratification), it’s best to sow them at the start of winter around winter solstice. This will allow enough time for the chill to be effective in triggering germination later.
Other annual and perennial seeds can be started any time.
I have best success when I divide my seeds into three sowing groups.
1) Seeds that require months of cold stratification (5 to 6 months before last frost).
2) Seeds needing moderate periods of stratification and / or hardy perennials and annuals.
3) Other annual and perennial seeds (1 to 2 months before last frost).
Find Your Frost Dates & Hardiness Zone
Average Frost Dates | Use this calculator at Almanac.com. Enter your city and state or province to find your first and last frost dates and number of frost-free days.
Ecoregion | Learn about the native plant and animal species and environmental conditions specific to your region to better understand why your garden choices matter.
Learn More: Understanding Frosts & Freezing For Gardeners
A Unique Milk Jug Method to Start Seeds Outdoors During Cold, Snowy Months
by Melissa J. Will
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Good luck with your winter sowing. If you’re like many gardeners, once you try it, you’ll want to experiment more.
Use these tips if you prefer to sow seeds directly outdoors before last frost without jugs.
~Melissa the Empress of Dirt ♛
How to Winter Sow Seeds in Milk Jugs
Supplies & Materials
- 1 pack Seeds cold-hardy
- Drill holes in base of clean milk jug to provide drainage.
- Cut open clean milk jug horizontally around middle leaving section below handle to form hinge. Cut should be at least 4-inches above base.
- Remove lid.
- Add 4-inches of moistened (water only) organic potting mix to base of milk jug.
- Sow seeds following depth instructions on packet.
- Label jug and add plant tag noting seed names, source, and sow date.
- Tape or tie milk jug shut around middle, keeping lid off.
- Place in sunny location outdoors away from wind or puddles.
- Check jug on sunny or warm days (above freezing) and water potting mix as needed.
- Transplant seedlings to garden following timing advice on seed packet.