Winter sowing is an easy and economical seed starting method. In this method, recycled plastic containers (like milk jugs) are used to create mini greenhouses for seeds to germinate and develop into robust seedlings. By using the winter sowing method, seedlings will already be acclimated to the outside elements and are ready for transplant when growing conditions are right.
For many, when they hear and refer to ‘winter sowing’, what comes to mind is an image of milk jugs in the snow. For others, they think of the process of starting seeds in a milk jug outside—but not confined to the winter months.
It’s true, winter sowing does take full advantage of the elements of winter that many seeds require or greatly benefit from in order to germinate. But what does this mean about when to start? And what about zones that have mild or even warm winters?
Below you’ll find a guide for determining the best time to winter sow. Because this method is not exclusive to those with long cold snowy winters, I will be using the term ‘winter sowing’ more broadly. Specifically, I’ll be covering the topic of when to start your seeds in milk jugs—or other plastic containers—outside.
How to use this guide
A helpful way to think about when to winter sow is to think not in terms of sowing on a specific date, but within a window of time. Finding the right window of time to winter sow is largely determined by what you are sowing, when your winter becomes cold, and your last frost date. As you learn to winter sow, even more important than knowing your zone, is becoming familiar with the winter weather patterns and characteristics in the climate you’re growing in.
Winter sowing made simple: the principles of winter sowing
There are two main windows for winter sowing:
When the weather in your area becomes consistently cold
6-8 weeks before your last frost date
When the weather in your area becomes consistently cold
This window is for anything requiring cold stratification (like native plants and perennials) followed by cool season vegetables, herbs, and hardy annuals.
This window extends to the start of the second window, and many seeds from this window can still continue to be winter sown at the start of the second window.
6-8 weeks before your last frost date
The start of this window is for fast growing cool season vegetables as well as your tender annuals; anything that is frost sensitive—including seeds for your warm season flower, vegetable, and herb garden.
Now let’s walk through this zone by zone.
Zones 1-6
In zones 1 through 6, winters are marked by the quintessential weather patterns that come to mind when we think of winter— these being, freezing (or just above freezing) temperatures and for many climates, periodic snow that lasts until spring.
In zone 6, winters may certainly have these characteristics, but winters may also be more mild for you depending on your area and the year. If you find that winters tend to be more mild for you, some of the guidelines for zones 7 and 8 might be more relevant to your winter sowing. Learning the characteristics and patterns of your winter is a simple way to know when to start winter sowing and what modifications might be necessary or beneficial.
Generally speaking, in zones 1-6, winter sowing is fairly straight forward. There are two distinct windows for when to sow: dead of winter and end of winter.
This recommended schedule for the first window for winter sowing applies to zones 1-6 when weather patterns become consistently cold and you can expect it to stay that way until spring.
Dead of winter: January through early March
Winter sowing in the coldest months is meant for cold loving seeds:
Seeds that require cold stratification
Seeds that need colder temperatures to germinate
Seeds that grow cold hardy plants
Not everything from this category needs to be winter sown right away — again, remember to think in terms of windows for sowing. Some seeds need the cold (like many natives and perennials), others simply benefit from it and thrive in cooler temperatures (like hardy vegetables, hardy herbs, and hardy annuals). Can you winter sow all of these at once as soon as temperatures become consistently cold? Absolutely. Can you wait, or sow in groups based on certain growing requirements? Absolutely.
The beauty of winter sowing is that as you leverage both nature’s way of growing from seed and the greenhouse effect, you have a lot of flexibility as for when to begin sowing.
What to begin sowing in the dead of winter:
Native plants
Perennials
What to begin sowing toward the end of winter:
Hardy vegetables
Hardy herbs
Hardy flowers
The reason behind winter sowing these cold loving seeds beginning at this time is not because they will start to grow right away, but in order for them to be in the perfect place to lay dormant, cold stratify (for those that need it), and to germinate and grow as soon as nature decides conditions are right.
End of winter: March through the end of April
In zones 1-6, March is still a great time to continue (or even start) winter sowing seeds from the list above that don’t require cold stratification. However, at this time, winter sowing begins to shift more exclusively to sowing seeds that require warmth to germinate and are vulnerable to frost. Things like:
Warm weather vegetables
Warm weather herbs
Tender annuals
If you’re unsure when to start your warm weather seeds using the winter sowing method, a general rule is to count back 6-8 weeks from your last frost date and start winter sowing them anytime in that window of 6-8 weeks. This allows for an early germination, and a smaller window of time where there is still a chance of frost resulting in the need to cover your jugs to protect them. Sowing these seeds within this window minimizes the maintenance required for the seedlings they will produce.
If you live in a climate that is especially cold up to the last frost date and is vulnerable to late killing frosts, you can start your tender annuals 4 weeks before the last frost date.
Now, you might be asking yourself, can I just winter sow everything all at once? That is, can you winter sow your cool season and warm season seeds together before March?
In general, I tend not to recommend winter sowing anything that is susceptible to frost (aside from natives and perennials that need cold stratification) before that window of 6-8 weeks before the last frost date. Can you put everything out at once in January and have great results? Yes, you can. If you choose to winter sow all of your warm and cool season seeds at once, the important thing to keep in mind is that if they do sprout especially early, they will need to be cared for in terms of watering and protection from freezes, and there might be avoidable losses.
Zones 7ish+
A lot of people like to rope in zones 7 and 8 with zones 1-6…and that’s fine! But after winter sowing in both a climate that experiences very cold winters as well as a climate with a more mild winter, I’ve learned that zones 7 and up is sort of the wild west of winter sowing. Once you start to understand the principles of winter sowing and how they interact with what you are sowing, your mild to warm winter weather patterns can work to your advantage.
Zones 7 & 8
Now, I will start by saying this: if you’re in zone 7 or 8, it might be that you’re able to follow the schedules for zones 1-6 very closely. But when you take into account that most of us in zones 7 and 8 have winters that start off warmer, followed by temperatures that can be all over the place—and to some degree, we are still able to grow all year long—you learn that some of the rules go out the window and the principles of the winter sowing method are what matter most.
In zones 7 and 8, winters tend to have a warmer start and are susceptible to erratic temperature surges and plummets—this can last for several months. As you become familiar with the windows for sowing, aim to remember that timing and modifications needed will vary based on how warm and how cold your winters get during these windows of time.
For zones 7 and 8, there are three distinct windows for using this method: fall, the coldest weeks and months, and end of winter. Not all mild winter climates will experience these windows for the same length of time, so it’s important to focus more on the markers of these windows and less on the dates and months.
Fall: September through November
When using this method, sowing that starts in September is meant for cool season crops that can be grown and harvested throughout the fall and winter, but will likely die back before the next growing season. It is also meant for plants that will overwinter for a head start on the next growing season. Things like:
Hardy vegetables
Hardy annuals
Hardy herbs
The coldest weeks and months: January through the beginning of March
The coldest weeks and months are meant for cold loving seeds. In climates with milid winters, I recommend starting these immediately at winter solstice. Seeds sown in this window include:
Native plants
Perennials
Things that can also be sown during the coldest weeks and months, or delayed and started closer to the end of winter:
Hardy vegetables
Hardy herbs
Hardy annuals
Many natives and perennials require cold stratification. In order to achieve this, they will need to be exposed to several days—and for some, even months—of temperatures somewhere between 33-40°F. Daytime temperatures can rise a bit higher, but if that is the case, consistent nightly temperatures in the 30s or below is really the goal. Without this cold period, this particular group of seeds will continue to remain dormant—or, germination rates will be very low. One thing you’ll need to determine is whether the area you’re growing in experiences a period that is cold enough to cold stratify your seeds.
If the area where you are growing does not experience a cold period like this, you can still use the winter sowing method for seeds that require cold stratification, but you will need to use artificial cold stratification first.
If this feels a little confusing and you’re not sure how this will work in your zone, one way around this is to stick to growing plants that are specifically native to your region or perennials that self sow in your area.
End of winter: February and March (6-8 weeks before the last frost date)
In zones 7 and 8 with cool springs, March is still a great time to continue winter sowing things like hardy vegetables, herbs, and flowers. Beginning in March and into April, winter sowing begins to shift more exclusively to sowing things like:
Warm season vegetables
Warm season herbs
Tender annuals
Zones 9+
I do want to state that I have not personally winter sown in a climate with very warm winters, where temperatures rarely drop below freezing—if at all. I do know it can be done—with modifications. That being said, I would not say that I am an expert on winter sowing in zones 9 and up. I would love to hear in the comments if you’ve winter sown in zone 9 or higher, or if you’re trying it for the first time.
When to winter sow in a hot climate
Similar to zones 7 and 8, in zones 9 and up, the winter sowing method can be used to start seeds for much of the year, apart from the hottest months. It works best when done between September and February. In zones 9 and higher, there are two main windows for winter sowing:
Fall: Beginning as early as September or when temperatures start to cool
Native plants
Perennials
Hardy vegetables
Hardy herbs
Hardy annuals
End of winter: 6-8 weeks before the last frost date
In zones 9 and higher, beginning as early as January, the focus of winter sowing will start to shift more exclusively to sowing things like:
Warm season vegetables
Warm season herbs
Tender annuals
Some winter sowing modifications you might want to use in zones 9 and up:
Monitor moisture levels more frequently.
Cover jugs with frost sensitive plants that have sprouted with a blanket on nights that have forecasted temperatures below freezing.
Apply less drainage holes to the base in order to trap in more moisture.
On especially hot days, break up the seel on the tape a bit in order to encourage air flow.
Keep jugs in the shade on especially hot days.
Keep jugs with seeds requiring cold stratification out of direct sunlight during the stratification phase.
Cold winter vs mild winter — my hot take
Here in the south, I am winter sowing in zone 7b, but I learned to winter sow and did it for years in Minnesota. Here’s what I have to say about how winter sowing in a climate that experiences very cold winters compares to winter sowing in a climate with a mild winter.
Cold winters
In Minnesota—where winters are long and harsh—winter sowing absolutely revolutionized the potential for my gardening. Not only was I able to start my own seeds months before the last frost date, I was also able to enjoy my garden sooner. I didn’t have to worry about transplant shock from using other seed starting methods, and I was also making pesto when my neighbors were still buying their basil starts from big-box garden centers. I was harvesting cucumbers and squash sooner; and I was making cut flower arrangements with my annuals when others around me were still anxiously awaiting blooms. Winter sowing in a climate with very long and cold winters extended my gardening season and maximized my harvests.
Mild winters
In the south, where I currently am, my winters are marked by a warmer start, followed by a few months of weeks that are cold, weeks that are warm, and weeks that are all over the place—in no particular order. Here in my humid subtropical climate, winter sowing is an amazing way for me to maximize my gardening all year long. I use the method for my early spring garden, for my summer garden, and for my fall and winter garden. The really amazing thing about using this method in a climate with mild winters, is that at certain times, the milk jug really functions similarly to the way a hoop house does. This especially helps maximize my winter and early spring gardening. I’m able to keep growing food and flowers for my garden no matter how warm or how cold it gets; I can always be succession sowing or adding to my garden using this method.
How I use this method in my mild winter climate:
Beginning in October:
Using this method for starting seeds in the fall works beautifully in a warmer climate because a lot of the time you don’t have space in your annual gardens as you are likely still harvesting through the end of October and even into late November depending on the timing of your first frost. This schedule works seamlessly; when things in the garden are starting to die back, things in the jugs are ready to be transplanted for my winter garden.
I use this timing to sow seeds for my late fall and winter vegetable garden. Things like kale, red lettuce, Swiss chard, spinach, and carrots.
I use this timing to sow seeds for winter flowering plants or spring flowering hardy annuals. Things like violas, snapdragons, foxglove, and larkspur that can be transplanted out when it’s still cold and overwinter for a late winter or spring flowering.
Beginning in December into early March:
I use this timing (winter solstice) to sow all of my natives and perennials—anything requiring cold stratification.
I use this timing (January & February) to sow more seeds for my cool season crops that I plan to add to my garden and harvest before the heat of summer. Things like, kale, lettuces, broccoli, sugar snap peas, and onions.
I use this timing (January & February) to sow seeds for my hardy annuals that I grow for my cut flower garden. Things like, bachelor’s buttons, larkspur, nasturtium, snapdragons, pincushion, and nigella.
I use this timing (February) to sow seeds for hardy herbs that I plan to add to my summer garden. Things like feverfew, calendula, marshmallow, spearmint, parsley, chives, lavender, and hyssop.
Beginning in March:
I use this timing to sow my tender annuals for my cut flower garden. Things like zinnias and cosmos.
I use this timing to sow my warm season vegetables and fruits. Things like tomatoes, cucumbers, peppers, eggplant, squash, and melons.
I use this timing to sow my warm season herbs, like basil and chamomile.
One aspect of winter sowing that I most enjoy is the opportunity I have to try new things each year at such a low cost. Of course, with all gardening, there are going to be successes and learning curves as you learn to winter sow. Some years will be better than others. Winter sowing is so incredibly life-giving to me and I hope you find that it is for you too.
What zone are you winter sowing in? I would love to hear below!
How does winter sowing work? Learn here!
Do you to be part of a winter sowing community? Join my winter sowing Facebook group!