Winter Sowing – Complete Guide To Starting Seeds In Winter


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Winter Sowing is a method of sowing and starting seeds outdoors in miniature DIY greenhouses that is simple, cheap, and effective. It allows you to get an early on starting growing plants, but without the expense, mess, and potential problems of starting seeds indoors or using grow lights. Winter Sowing is by far my favorite method of starting seeds.

Every year I grow seeds from dozens of different species, both flowers and vegetables. And I Winter Sow almost all of them. I’ve been doing this for 10 years, and have gained a wealth of experience. Furthermore if you’ve looked into Winter Sowing videos, chances are you’ve seen my thorough video-tutorial. But, here I’m going to share my knowledge in written form.

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In this article I’m going to give you an in-depth overview of the benefits, when you should winter sow, and a step by step guide how to do it. And I will share specific tips for each step of the process that I’ve learned over the years, so you can learn from my experience.

Digital table of contents

What is winter sowing?

Winter sowing is the process by which we sow seeds outdoors in the winter, contained within mini-DIY green houses! Winter Seed Sowing allows mother nature to cold stratify our seeds naturally outdoors, as well as hardening them off. The miniature DIY greenhouse stays warmer at night than the surrounding air, which allows seeds to germinate and survive outdoors much earlier in the season.

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Winter Sowing is probably my favorite Winter Gardening chore as I can get my hands a bit dirty while anticipating all the seedlings that will germinate. It really is a great way to keep our ‘gardening’ hats on during the off-season.

Winter sowing has big benefits!

Winter sown seedlings have many benefits over traditionally sown, or even indoor grown seedlings. These are just some of the main benefits I’ve noticed from winter sowing my seeds over the years.

No hardening off period

Winter sown seeds acclimate to the environment from the day they germinate. And this continues into Spring, making the plants tougher or ‘hardier’ to cooler temperatures. There will be no ‘cold shock’ when transplanted to their final location (unlike indoor-sown seeds).

Larger seedlings

Since we are growing our plants in miniature greenhouses, we get the benefit of warmer temperatures. Warmer temperatures mean plants are more active aka- more photosynthesis, which means larger, healthier seedlings.

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Here is a container with Wild Strawberries (trying to escape via runners!)

Cost

Winter sowing is nearly free. You don’t need to spend any money on pots since you can reuse old containers. Your only cost will be potting soil, seeds, and possibly duct tape for sealing up the containers.

No fungus

The winter sowing containers are open to the environment and exposed to sunlight. The air exchange they receive combined with the sun keeps fungus away (unlike indoor grown seedlings).

No expensive grow lights

Since winter sown plants use the sun….that means we don’t have to spend money on expensive grow lights, heat mats, or other accessories.

Doesn’t take up space indoors

By winter sowing our seeds outdoors, we don’t have to dedicate a corner of a room or countertop space for growing our seedlings. Now, if you are growing a large number of plants for a vegetable garden or perhaps designing a new flower bed, you can get all your plants started for less space.

Repurpose & reuse old containers

Winter Sowing allows us to reuse our old containers, plastic totes, and similar items for growing our plants. And we can reuse them for multiple years (in general). And when they do eventually fall apart, you can recycle them as normal.

Save time during the growing season

By winter sowing you are effectively performing a garden chore in the winter….which means you don’t have to plant seeds in the Spring. Thus, you are effectively giving yourself some time back during the growing season by winter sowing!

When should you start winter sowing?

What time of year you winter sow seeds will depend on what types of seeds you are winter sowing. Some seeds require an over-wintering period in a cold-moist environment, known as stratification. While others will readily germinate in a warm moist environment. Also, some seeds and seedlings can survive a cold frost, while others will be killed.

As a general rule, cold-hardy perennials or seeds that require cold stratification such as Echinacea or Liatris can be winter-sown from late Autumn through early Spring. While vegetables or tender annuals that cannot survive freezing temperatures should be Winter Sown a few weeks before the last frost, or before one would traditionally start the seeds outdoors.

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For me, I start all my native perennials or seeds that require stratification in December or January, usually winter sowing them over the holidays. I usually have some time off from work then, and can plant 20 jugs and 10 trays in as little as a few hours.

When it comes to my vegetables, I generally sow them six weeks prior to last frost date for my area. Once they’ve sprouted, if I notice the overnight temperatures is going to get too far below freezing, I just bring them into my garage until morning.

*Note – I have a special variation of winter sowing for tomatoes and peppers

What kind of containers should you use

Traditionally Winter Sowing is done by using milk-jugs, or in miniature greenhouses (trays with domes). But there are other creative solutions available. I usually do a mixture of milk-jugs and miniature greenhouses (trays with domes) that are filled with six-pack inserts. No matter what kind of containers you choose, they should have a few common features.

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Examples of wintersowing containers

Requirements for containers used in winter sowing

There are several physical characteristics or features that any winter sowing should have. First, it must be translucent to allow sunlight to reach our seeds. Second, it needs to have air holes in the top, and drain holes at the bottom. Third, we have to have a way to open the container up for when the outside temperatures warm up. Finally, it needs to be big enough to for the seedlings to grow large.

Let’s look at each of these requirements more closely….

Translucent

Since winter sowing is basically germinating and growing seeds in miniature greenhouses, we need to make sure that sunlight can pass through our container. This works for any clear container or 2-liter soda bottle, or the traditional milk jug.

If a container looks opaque, or you aren’t sure that light can pass through, don’t use it for winter sowing.

Without sunlight the plants will not be able to grow, nor will we be able to take advantage of the greenhouse effect. So, go for milk-jugs or clear containers that allow sunlight to pass through. And avoid any container that is opaque.

Air flow from above

All winter sowing containers should allow some air exchange with the environment. This air flow will help reduce any algae that may form on top of the soil as well as eliminate any chance of fungus. For jugs, it also can add a small amount of moisture during rains or snow.

For a simple milk-jug or 2-liter bottle, we can just keep the lid off. For any container that has a large lid, such as plastic take-out boxes or Tupperware, we can add air holes in the top using a drill or knife.

Drainage holes

All winter sowing containers must have some drainage holes. This is necessary to prevent soggy roots, root rot, or fungus. You simply add them using a drill, soldering iron, or knife.

Must be able to open it for cooling

When discussing ‘Winter’ sowing, we often only speak of the colder aspects. But we do need to consider what happens when spring temperatures warm up. In general our seeds will germinate when it is still very cool outside, so we can keep our ‘lids on’ during cooler temps to take advantage of the greenhouse effect. But as Spring progresses and temperatures warm up near 70F (21C), we need to have a way to open our containers so we don’t ‘cook’ our seedlings.

Opening up a winter sowing container can be as easy as removing a lid from a plastic container or removing the dome from a greenhouse. For milk-jugs of water bottles, we just need to peel off tape and pull the top half back (using the hing we make).

Volume

In general we want to grow our seedlings to a large size for transplanting, so we need to make sure our containers are large enough to accommodate a healthy root system and have enough space for top growth. Furthermore, not having enough potting soil will make containers more prone to drying out.

As a general rule, containers used for winter sowing should be large enough to allow for 3″ of soil depth, be at least 3″ diameter, and have 6″ of room above the soil. But this is a guideline, not a rule. For instance I’ve successfully winter sowed in milk-jugs that only had 2″ of soil depth. This worked fine because the larger surface area means I have a large volume of soil, even though the depth was only 2″.

Video Tutorial to Winter Sowing

Below is a complete video tutorial I made for Winter Sowing a couple years ago. It discusses all aspects to consider, and is essentially the ‘video’ version of the steps listed in the next section. But I thought I would include it before the rest of the article, as it does a great job at explaining the entire process.

How to Winter Sow – step by step

1 – Materials

  • Proper containers (see above) – A clean milk jugs, or similar. Also a plastic container/pot with covered dome works (w/ air flow and drain holes)
  • Scissors, sharp knife (pocket knife, box cutter), drill or soldering iron
  • Potting soil
  • Watering can or sprayer
  • Seeds

2 – Preparing containers for Winter Sowing

In my experience all containers require some modification, even if you purchased a black tray with a dome. At a minimum you need to make sure that there are drainage holes to allow excess water to flow away, as well as that there are ventilation holes in the top.

For a plastic container or mini-greenhouse

Add air holes: Use a pocket knife to add drain holes to the 1020 tray if none are present. Holes should be 3-6 mm diameter (1/8″-1/4″). Simply set the tray on a hard surface upside down, and use a sharp pocket knife to stab a slit into the bottom. Then, with the knife blade inserted, twist the knife 90 degrees to form a hole large enough to allow water to drain.

You need to also use a knife to poke 6 – 8 holes that are 1/4″ diameter (6 mm) in the top of the dome to allow airflow.

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Two trays that I’ve winter sown. Note the ventilation holes.

Find the trays with domes on our Recommended Products Page.

Preparing milk-jugs (or similar containers) for winter sowing

For preparing a milk-jug, or 2-liter bottle, there are just a few steps to complete. I’ve found that it is important to carry out these steps in order though, as it makes the overall construction process safer and easier.

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Winter sowing containers benefit from having some airflow at the top. For jugs, this is as simple as leaving the lid off. For trays or mini-greenhouses, about 6 small holes to allow air to pass over the soil is enough.
Wash the milk-jug

Squirt a few drops of liquid dish-washing soap into the container, add some water, and then shake it for 30-60 seconds. Next, rinse it several times until no soap bubbles come out when you drain it. Finally, place it somewhere to dry if you’re not going to use it for a while. I like to place it on an up-side down tomato cage to let it dry.

Add drain holes

Add 4-6 drain holes in the bottom of the jug. You can do this using one of several tools – just make sure you are careful & comfortable with all of them. Several common methods for adding holes is to use a cordless drill with a 1/4″ (6 mm) drill bit, a hot soldering iron, or even a simple pocket knife (my personal choice).

Now, before you just start poking holes randomly in the bottom, examine it first. Add your holes on the outside edge of the bottom, or along a pathway for water to escape. If you just add a hole on a flat surface on the bottom, then water may not be able to drain out depending on what surface you place the container on!

Adding drain holes with soldering iron or glue gun (no glue)

You can use a hot soldering iron or glue gun to melt drain holes into the bottom of your container. In my experience it works best on milk jugs. Just make sure you are in a well ventilated area like a garage (with door open). Simply plug in and heat up the soldering iron, and carefully poke drain holes in locations where water can escape.

Using a drill

If you are using a thick plastic tote, then you most likely need to use a drill to add drain holes, but you need to be careful. Pressing too hard with the drill can result in cracking plastic and breaking your container (aka a blow out). This method does work, but is probably my least favorite due to the uncertainty.

The best way to add drain holes with a drill is to first cut your hinge for better access to the bottom. Then, open your container up and place it on top of a scrap piece of wood. Then, drill your hole as the wood backing will greatly reduce the likelihood of splitting/cracking. Use a 1/8 bit at minimum to allow for a large enough hole for drainage.

Cutting drain holes with a pocket knife

Using a pocket knife to cut drain holes is by far my preferred way to add drain holes to milk jugs, 2-liter bottles. It sounds dangerous, but I find that it is perfectly safe as long as your knife is sharp, and you haven’t cut your hinge yet, as then the container is still relatively sturdy.

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But you can hold the two-liter bottle against a hard surface, or milk jug by the handle, and then carefully stab a slit into the bottom edge of the milk-jug or thin-walled container. Angle your sharp knife so that the blade is not pointed at your other hand, which is holding the jug. Then, once the knife slit has been made and the blade is inside the jug, twist the knife 90 degrees to form the hole and remove the blade. You’ve now made a large enough drain hole safely.

Cut a hinge

A hinge needs to be added to milk-jugs, 2-liter soda bottles, or other similar containers. The reason for doing this is that it allows you easy access to sow your seeds, and it will allow you to open the container up once daytime temperatures get above 65F. Finally, you also need to open the container up to access your seedlings for transplanting or separating.

To cut your hinge, simply get a box cutter or pocket knife, and cut horizontally around the jug, leaving about 1-2″ at the base of the handle. You can also do this with scissors or a finely serrated knife if you prefer.

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Cutting the hinge is very easy with a sharp knife. I just have a regular pocket knife. You can also use scissors or something similar.

3 – Potting soil. What types and how to prepare for winter sowing

I’ve found over the years that many people get hung up on what kind of potting soil they use for winter sowing. I generally don’t fuss over the brand, but I will say that in general you don’t want to buy the ‘cheapest’ potting soil for starting seeds. You want a fine texture for starting seeds.

Most potting soils are primarily made of sphagnum peat moss, which is perfectly fine. But cheap potting soils will have less perlite (little white balls) and more large twigs. Perlite helps retain air, while twigs just get in the way and can possibly damage seedlings during watering.

So, spend a few more bucks and get something good. In my experience the absolute best potting soil for starting seeds is ProMix, but other high-end soils are good too. You just want to make sure there are few twigs (if any) in your soil. If you do have some ‘twiggy’ soil, save it for when you transplant seedlings to larger pots or containers.

Preparing the soil

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Now, to prepare your soil, you simply want to get it really wet. As in, sopping wet. I dump a lot of soil into my wheelbarrow in the garage and get it heavily saturated. That reduces the chances that I ever need to water the containers before Spring. Once your soil is well saturated, you can simply fill your containers to 1/2″-1″ (12-25 mm) below the top edge.

How much soil do you need for winter sowing?

For most plants, 2-3″ of soil depth is more than enough for germination, and for the plant to develop several sets of true leaves. It will even develop a large root system if you thin the seedlings. You don’t need to use larger depths 6-10″ unless you are germinating acorns or tree nuts.

In fact I have used little six-packs for years to winter sow, and they are only 2.5-3″ deep, with small surface areas. These small surface areas mean I will have to provide supplemental water periodically, but it is still more than adequate to grow most flowers and herbs.

For DIY containers (milk jugs & similar), the smaller the surface area of the container, the deeper the soil should be. I’ve gotten away with 2″ of potting soil for one-gallon milk jugs, but for smaller surface containers (like 1/2 gallon milk jugs) I fill it 4″ deep.

Can you use compost or garden soil instead?

Regular soil from your garden, top soil, or compost should not be used for winter sowing. They are fairly dense and don’t always have sufficient water holding capacity.

4 – Sowing seed

In general you should only sow one species per jug or container. Doing more than one species will get very confusing unless you are able to identify your seedlings.

If sowing store bought seed, simply follow the instructions on your packet for planting depth. For how many seeds to sow, I always assume the seed I am sowing will have a 50% germination rate. And then sow based on how many plants you want….so, if you want 10 plants, sow at least 20 seeds, etc. Remember, seeds are generally very cheap and you can always thin them later.

If you are unsure of planting depth and cannot locate the information, then just plant shallow. A rule of thumb is to not plant deeper than three times the smallest dimension on the seed. And for tiny seeds, simply scatter on the surface and press in with your thumb (they often need exposure to sunlight).

So, choose your container size based on the number of plants you want. If you are only looking for a few plants, you can simply sow sparingly in a milk jug and just grow them to a large size. If you want many plants, sow heavily knowing that you will just separate seedlings later on.

5 – Sealing your container

Once your seeds are planted, it is time to seal your container. If you are using the store-bought mini-greenhouse tray w/ dome, then you should tie it with twine across both the length and width. If you are using milk-jugs or the like, then use duct tape to close the hinge.

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After you have sealed with duct tape, pick up the container by the handle and give it a gentle shake to test the seal. If it feels secure, then it should be fine until Spring.

6 – How to label or tag containers

When it comes to labeling containers, if you are using store bought six packs, I find that you can simply apply masking tape to the outside of the container and label it with a sharpie marker. This usually lasts until well into summer, by which you probably transplanted your seedlings.

If you are using plant tags, milk-jugs, or plastic containers, then I find that labeling with a wax pencil (known as a ‘China Marker’, available here) works best. The wax lasts almost forever, and never seems to fade on plastic even when fully in UV radiation.

7 – Where to place containers outdoors

Where oh where to place my winter sowing containers??? Ok, here is the thing about where to place your containers….Common sense tells us that because it is Winter, nothing will germinate because it is cold…right?

Well, unfortunately for us winter sowers some species of seed can germinate quickly if the temperatures get warm enough and they are in a moist environment. And our little winter-sown greenhouses will provide just that – a warm enough & moist environment. I have personally had numerous species of native seed germinate during a warm week in February some years ago. This resulted in me taking my containers indoors during the remainder of Winter when outside temps were going to be far below freezing – I didn’t want to kill my prematurely germinated seedlings!

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Preventing premature germination while winter sowing

So, how do you prevent premature germination when winter sowing? Simply keep the winter sowing containers on the North side of your house, or in the shade during Winter. Then, move them to a location that gets morning sun and afternoon shade once spring approaches. This way, if you do have a warm sunny day in the middle of Winter, nothing will germinate

Other location factors to consider

Some other items to keep in mind in regards to placing containers is that you want to keep them exposed to the elements. But, if you live in the Midwest, you also don’t want them blowing away! I’ve found that if you push all containers together so they are touching they are less likely to blow around in storms, etc. They kind of act as a single mass when pressed together.

Also, this should go without saying, but keep them somewhere that flooding isn’t a problem and that any excess water can drain out the bottom.

I keep all of my containers/jugs in a Northeast corner of my house that gets zero sunlight. It is exposed to all the cold and much wind, but not windy enough they would blow away. I place them there in December/January, and move them to some tables that receive morning sun around the beginning of March. That is where they will stay through Spring.

8 – Watering winter sowing containers

Winter sown containers generally don’t need watering, as they usually have a large amount of soil that will hold moisture well. However, smaller containers or plug inserts may require watering occasionally. Containers that hold a large volume of soil almost never need supplemental water after being sown (in my experience). But if you are winter sowing with a tray/dome in six-packs, you will likely need to add water at some point.

To determine if you need supplemental water, simply pick up the container and judge if it feels somewhat heavy. If it feels very light, then add water.

To water winter sown containers, you can water from the bottom by placing a container in the large tray filled with water for about 30 minutes. Or, you can use a one-gallon pump sprayer and spray through the milk-jug opening at the top.

9 – Germination

As Spring approaches, when temperatures are still cool but don’t get too far below freezing, you can move the containers to a location that receives morning sun and afternoon shade. The warm temperatures will have your seeds sprouting species by species over the course of a few weeks.

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Looking down a milkjug at some Elderberry seedlings I winter sowed that are just starting to germinate.

You do not need to take major action as long as the outdoor highs are in the lower 60’s Fahrenheit or cooler. But in my experience on sunny days, if the outdoor temperatures approach 70 Fahrenheit (21), then it is time to open up the winter sowing containers to prevent your seedlings from being cooked.

10 – Opening the containers when it gets too hot

Once daytime high temperatures are getting a bit warm, we need to open our containers to keep them from overheating. Now, this generally will not happen until your seedlings are of a decent size, and they are already acclimated to the cool evenings. So, you shouldn’t have to worry about putting the lids back on.

On sunny days, if the outdoor temperatures are approaching 65-70F (18-21 Celcius), you need to open the lids to your winter sowing containers to prevent the seedlings from dying due to becoming too hot. Do not take chances – just open the containers. You do not want to lose your seedlings and have your hard work wasted.

If you have opened your containers but know that a freak overnight freeze is coming, you can always place them indoors for that evening. When it comes to cold hardy perennials, I don’t worry about frost protection once I’ve taken lids off. But for tender vegetables, I may bring them into the garage if necessary.

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Once outdoor temperatures get to 70F, the lids come off or they go back to the shade!

Also, once the lids are off, you should now be treating these containers like any other container grown seedling that will stay outside. So, regular watering when needed (preferably in the morning only), and protecting from deer/rabbits or cabbage white caterpillars!

11 – Transplanting, thinning, or separating seedlings

Once your plants have grown to a decent size, where they have about 3 sets of true leaves or are several inches tall you should consider whether you should thin, separate, or directly transplant them.

If you’ve heavily sown your seed, and have a high germination rate, ask yourself how many plants you actually want? Or how many you have room for? Then either thin, or separate and pot up individual seedlings to larger containers based on the number you truly want. You can always leave extras in the jug for insurance.

***Note – if you are not sure how to separate seedlings, we have a detailed guide on how to safely separate them.

But if you only have room for 10 plants, but you have 30-40 in the jug what should you do?

  1. Thin the extras, growing the remaining 10 plants to a much larger size over a few weeks.
  2. Separate the seedlings into individual containers, and grow them to a larger size over a few weeks
  3. Transplant directly into the garden, using a method known as the ‘Hunk-O-Seedlings’

So which option would you choose? Well, if deer and rabbits are a concern then I would choose option 1 or 2 to grow my plant very large so that it would be more likely to survive browsing from herbivores. If I wasn’t concerned about deer and rabbits, whether because they weren’t around or I had a strong aroma plant then I would choose the hunk-o-seedlings method (next section).

12 – Hunk-O-Seedlings method

Ok, so I must talk about this method for transplanting seedlings to a final location. The process that is affectionately known as the ‘Hunk-O-Seedlings’ method is where you literally cut out hunks or chunks of seedlings with a pocket knife, and plant the entire clump in it’s final location. No thinning or separating of seedlings – you plant the whole ‘hunk’ and let nature sort out the winners and losers.

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Yes, these images are of me using the ‘Hunk-O-Seedlings’ method on Plains Coreopsis seedlings.

There is one other important tip I have for this method – dig your hole before you cut your ‘hunk’, as that way you don’t have to set down the clump of seedlings. you can then just place it directly into the hole.

This method works. It looks a bit sloppy, but if you are planting some Bee Balm, Wild Bergamot, or Mountain Mint – it works great. The strongest of the specimens will eventually dominate the weaker seedlings and shade them out. From the original ‘hunk’ you will be left with one or two healthy, vigorous plants by the end of the season.

You don’t need to overthink this method – just get a regular pocket knife or similar, and start cutting!

What seeds are good for Winter Sowing?

Just about any type of seed can be winter sown. And almost any species that is cold hardy to your area, or native to your area can be winter sown and be fine in freezing temperatures.

The only real concern with winter sowing some types of seed is that there are some species of tropical seeds that cannot survive being frozen, and also seeds from certain woody shrubs or trees (acorns, for example).

Perennials

Any perennial that is cold hardy to your growing zone, or native to your area can be winter sown as early as Autumn. Look up the specific species stratification requirements (if not on a package) and make sure you Winter Sow at least that amount of days before your last frost date.

Vegetables

For vegetables that can be winter sown, you simply winter sow them about 3 weeks before you would normally plant the seed outdoors. This allows them to germinate early from the greenhouse effect as well as harden them off.

Winter sowing tomatoes and peppers

I have a list of vegetables that can be winter sown below. But there are two species that are conspicuously absent from it – tomatoes and peppers. I have a special method for sowing tomatoes and peppers that is similar to winter sowing, but will involve bringing them inside at night. However, I grow 10″ tall tomatoes in six weeks using my method. I have a detailed article and video for this process here.

Annuals

For annual flowers, you can winter sow them 3-4 weeks prior to the last frost date. Keep them in the sun at all times, and make sure they don’t dry out. This will allow them to grow to a decent size prior to the last frost date, and they will be hardened off.

List of flowers, vegetables, trees & shrubs that can be winter sown

The list below is by no means comprehensive, as there are thousands and thousands of species that can be winter sown. The key factor is to know the cold-hardiness of the species, and adjust timing based on that. But, below I’ve compiled a list of 21 flowers, 21 vegetables, and 21 species trees/shrubs that can be winter sown.

Species that are cold hardy to your zone can be sown early in Winter, while annuals and most vegetables should be winter sown 3-4 weeks earlier than when you would normally plant the seed outdoors. And remember, plants that can be killed by a frost should be winter sown just a few weeks before the last frost (many vegetables and all annuals). And if a particularly hard freeze is expected after they’ve germinated, just move the jug into the garage for the night.

FlowersVegetablesTrees & shrubs
Anise HyssopArugulaApple*
AstersBeetsBlack Cherry*
BeebalmBroccoliBlack Locust
Black Eyed SusanBrussels SproutsBlack Walnut*
Blanket FlowerCabbageBuckeye
Blazing StarCauliflowerButternut*
CoreopsisDillButton Bush
CosmosKaleEastern Redbud*
EchinaceaLettuceElderberry
IronweedMintFlowering Dogwood*
Joe Pye WeedOnionsHackberry
Larkspur (Delphinium)OreganoHickory*
LiatrisParsleyMountain Laurel
MilkweedPeasNinebark
Mountain MintRadishOak*
Obedient PlantRaspberryPawpaw*
PenstemonSpinachPersimmon*
PhloxStrawberryRed Cedar
Sunflowers (all Helianthus sp.)SquashSpicebush*
VioletsSwiss ChardWhite Cedar
ZinniaZucchiniWinterberry
*Do not let these seeds completely freeze. Keep in unheated garage or shed during coldest parts of winter

Can you direct sow seeds in Winter?

There are many species of plants that can be direct sown in Winter. Squashes, gourds, tomatoes, as well as any cold-hardy perennials can be direct sown in Winter. I usually get some ‘free’ pumpkins and gourds from seeds that germinate naturally in the woods, or near my compost piles. And in my vegetable gardens I always have volunteer cherry & yellow-pear tomato plants that germinate from seed that was from decaying tomatoes I never picked.

But there are some risks – first, squirrels, rodents, and birds may eat the seed before Spring. Second, for vegetables, they may have a slower start than if you Winter Sowed them, or started them indoors. And 3rd, there are many species (mostly tropical) of seed that cannot survive completely being frozen for long periods of time.

Green stuff on top of soil in winter sown containers

By mid-Spring when all your plants are germinating, you may notice that the surface of the soil is covered in a green film. This is algae or young moss, and while it may look a bit gross it won’t harm your seeds or plants. The seeds you planted will grow right through it, and be healthy. This algae is ubiquitous, and just happens to grow well in moist environments without much air flow – like a winter sowing container.

In fact, once you transplant the seedlings to either their final location, or to a larger container, the algae will vanish with more exposure to sun and wind.

Can you winter sow tree seeds?

When it comes to winter sowing tree seeds, yes you can do it…but there is a catch. While many species of tree need a long cold-moist stratification period, many (if not most) cannot survive being frozen solid. I can give you plenty of direct experience where I found out the hard way that acorns, hickories, pawpaws should never be frozen solid. Nor other berry type seeds such as Spicebush should be frozen. But – you can still winter sow them.

The way to Winter Sow tree seeds is to first, protect them from squirrels. And second, to keep the seed from freezing solid you should either bury the container to half it’s depth in the ground, or just keep the container in an unheated garage or shed during the coldest part of Winter, when it may be at risk for being completely frozen.

Also, many tree seeds have cold-stratification requirements of 120-180 days! So, you need to get these in the cold in early Autumn. For instance, Black Walnuts should be Winter Sown not long after they fall from the tree, as should Black Cherry, Hickory, and Dogwoods.

Can Winter Sowing containers be reused?

You can reuse Winter Sowing containers year after year, or until they fall apart! For milk jugs and bottles, simply empty all the soil out and give it a thorough rinse with the hose. Then, set it out to dry. I actually hang my milk-jugs on a rope off some shelves in my garage to save space.

Final thoughts

Ok – if you’ve made it this far, congratulations! I didn’t expect to write such a long and detailed guide to Winter Sowing, but I guess I got carried away.

Winter Sowing is just about the easiest, cheap, and effective method to get an early start on germinating seeds. I’m not just writing about winter sowing, I really do it…every year. It is by far my preferred method to start seeds as you get larger plants earlier in the season, they are healthy and vigorous, and they are hardened off.

If you have any questions please write to me and I will try to answer them, or just drop a comment at my YouTube video I made on Winter Sowing. I try to answer all comments on my channel. Good luck!

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Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over 10 years. I hope to share some of my knowledge with you! You may have seen some of my videos I create on our YouTube channel, GrowitBuildit (more than 10 million views!). You can find my channel here: https://youtube.com/@growitbuildit Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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