The benefits and all the steps needed for milk jug winter sowing - starting vegetable and flower seeds in containers outside during the winter months. You'll love how easy this is!
A few years ago I learned about something called winter sowing, a practice where you start seeds in recycled containers and then leave them outside to grow slowly through the winter months.
I think it started in the far north to try and give the short-seasoned zones a bigger sowing window, but even in my more mild PNW zone I was intrigued for a few reasons, even though I've been starting seeds easily indoors for years.
- First, I've pretty much maxed out my indoor seed starting space and I always have more I could be growing.
- Second, since the seedlings were already outside, the major part of 'hardening off' (getting them acclimated to the outdoors) would naturally happen.
- And third, there are some seeds that benefit from a period of cold (known as seed stratification) that again happens naturally in the containers outside, bypassing any need to soak and refrigerate seeds. The seeds that need it are mainly flowering perennials, but it would definitely make them easier to start.
So I tried it, the first year sowing a bit later on March 3. I planted lettuce, kale, cabbage, broccoli, alyssum, and hyssop in six milk jugs.
Hyssop is a perennial that requires cold stratification and while most of the seeds didn't grow for me, three did.
The first year they grew a bit without flowering in the sunken garden, and the second year they flowered beautifully. So I count the milk jug stratification as a success, even with only three! (Plus the cost of even small perennials in 4-inch pots are now around $5-6, so I saved even with most of the seeds not germinating.)
The second year I started the seeds in mid February and to be honest, didn't notice any difference in the growth by spring of the later planted set (you can scroll down to the starts in April from each year).
TIP: In the second year I also experimented with other recycled containers, specifically a clear clamshell plastic container that held spinach.
This clear container burnt the new starts with even a small amount of sun and it was harder to keep the lid propped (the milk jug tops are always open), so I only use milk jugs now for outdoor sowing.
Benefits of Milk Jug Winter Sowing
Here's what I've come to love about starting some seeds in milk jugs during the winter:
- You can start many more seeds than indoors (usually), saving money from buying plants in the spring.
- You can grow harder-to-grow perennials like milkweed and hyssop because of the natural cold stratification that occurs.
- It's easy and cheap - you need only household supplies, potting soil, and seeds.
- You can start seeds when there's not a lot of other things going on - it's a nice winter gardening task.
- It takes very little time, both in sowing and monitoring. They grow on their own and are ready to be planted out when you are.
- The time and aggravation saved from having to totally harden off the seedlings is priceless (can you guess that's my least favorite thing about starting seeds??).
What Seeds are Best to Start in Milk Jugs?
Before we get to the how of sowing seeds in milk jugs, lets talk about the best seeds to plant in them.
You want to focus on plants that are hardy and take some cold normally, so NOT tomatoes, peppers, or other heat-loving plants.
But there are plenty of choices as you can see below.
Annual & Perennial Flowers You Can Winter Sow in Milk Jugs:
- Bachelor’s buttons
- Bells of Ireland
- Bee Balm
- Sweet Peas
Cold Hardy Vegetables & Herbs You Can Winter Sow in Milk Jugs:
- Asian Greens
- Bok Choi
- Brussels sprouts
- Spring Onions
- Swiss Chard
When to Start Seeds in Milk Jugs
In most zones you can start winter sowing in milk jugs and other containers outdoors as early as January. It really won't help to plant earlier, though, as I found out - mid February to early March results in similar growth.
It's because nothing will actually grow during the coldest months, but the seeds that need the cold stratification will get it and the others will start growing as the days lengthen and warm, growing into hardy seedlings.
To be honest, I've just started seeds I had that fit the lists above when I had the containers and time, never worrying about last frost date.
That said, you can go by your last frost date and the suggested planting times listed on the seed packets, timing your containers to be ready for transplanting into the garden at specific times.
Milk Jug Winter Sowing Step-by-Step
1. Gather Supplies & Prep Milk Jugs
The supplies you need are simple:
- milk jugs or other recycled containers
- scissors and/or box cutter
- duct tape
- permanent marker
- drill (or other way to make holes in the bottom of the jugs)
- potting soil
- plastic seed labels
How do you clean milk jugs for winter sowing?
Clean used milk jugs or other recycled containers by rinsing thoroughly, then add soapy water and shake it well with the lid on to clean. Drain, rinse again and let dry.
How to cut milk jugs for winter sowing:
- Use a box cutter to create an opening to one side of the base of the handle (or use the point of your scissors if they're sharp).
- Use scissors (I find it safer than using the box cutter all the way around) to cut around the milk jug, keeping level with the base of the handle.
- DO NOT cut all the way around, but stop before the handle, leaving about an inch to create a hinged top.
Make Drain Holes
Once your jugs are all cut, you need to create drainage holes. I've tried a nail and hammer, but jugs are surprisingly thick, so a drill works the best and fastest.
Set the jug base (with the lid open) on a scrap piece of wood and make holes all over the bottom with the drill. Repeat with all your containers.
2. Gather Seeds & Labels for Sowing
Decide what you will plant in your jugs.
Sometimes I choose one variety or type of plant for a jug, like white and purple alyssum, and other times I will make three rows of similar plants, like kale and two types of cabbage.
Write the type and variety on a plastic label with a permanent marker.
I like to get the seeds and markers all ready at once so I can plant all the jugs at the same time.
3. Sow Seeds In Prepared Milk Jugs
- Add moistened potting soil to each jug at a depth of about 3 inches.
- Sow the seeds either in rows or scattered if using just one seed type.
- Spray the seeds with water.
- Cover the seeds with more potting soil. It should ideally be moistened, too, but I had run out of soil and used a dry seed starting mix to cover the seeds, which I just wetted with more sprayed water.
4. Close & Label Milk Jugs
- Once all the containers are planted, close the jug 'lid' you created and use duct tape to cover the cut line all the way around the jug.
- Write the contents and date of sowing in large letters on the duct tape. They may fade a bit over the months, so I like to write it in two places.
- DO NOT cover the top openings with the lids - this provides ventilation (which is why they are superior to clamshell containers in my book).
TIP: You can also number the jugs and use a page in your Garden Notebook to record what you sowed in each container according to it's number. This will help you compare from year to year what grew well and to keep notes.
5. Place Milk Jugs Outside & Monitor
Set your jugs outside and let nature do it's work! The best place is a sheltered place with eastern exposure (morning sun/afternoon shade) - though sheltered can just mean the eaves of a house.
Basically a place that they won't drown in water or snow, but will get some moisture, and won't be fried by afternoon sun as the days grow longer.
However, I've grown them on a south-facing deck and western facing patio and they've been fine - you just have to monitor them more, moving to sun or shade as needed.
Monitor Containers Over Next Few Months
Water: You'll need to make sure the containers aren't drying out - water gently through the top opening if needed.
Sun: If there's too much sun too early, move jugs to a more shaded area. As the weather grows warmer, you may need to move them to a shady place until transplanting - you just don't want them to bake inside their little greenhouses.
6. Harden Off Just a Little
While these seedlings are hardier than what is grown indoors, they will still benefit from acclimating them to being completely uncovered.
- When getting close to transplant (2-3 weeks out), start opening tops on warm days, keeping the lids on at night (the duct tape usually holds to keep them closed at night).
- If days get and stay pretty warm (sunny and 50s-60s), keep lids off completely.
- One week before transplanting, keep lids open day and night near where they will be planted to be ready for garden.
7. Transplant Seedlings into Garden
To transplant the seedlings into your garden, make sure the soil in the containers is very moist and use a small trowel to remove the section you need (like a row of spinach, etc.).
Gently pull apart the seedlings, separating the roots as you do, and plant in a hole prepared with organic fertilizer.
Cover the roots with soil, pressing down to make sure the roots come in contact with the soil, and water well.
TIP: If the seedlings are small and you're not sure about your spring weather, cover them with row cover held up by metal hoops until they are bigger.
This is an almost foolproof way to have seedlings ready early!
Even though they were on the smaller side, most survived when transplanted, saving me time and money. I will always start some seeds this way each year, to go along with my indoor seeds.
Milk Jug Winter Sowing FAQs
You can use almost any recycled plastic container for winter sowing - Opaque milk and water jugs, food containers with clear plastic tops and two-liter soda bottles (cut in half like milk jugs). If it can hold 3-4 inches of soil, you can probably use it.
That said, my experience is that the opaque milk and water jugs are the best - they are least likely to burn plants as the weather warms vs. clear plastic and are self ventilating (you have to remember to open the lids of clamshell type containers on warmer days).
You can winter sow perennials, hardy annuals and vegetables generally January to March, but this is depending on your gardening zone. The further north you are, the later you can sow the seeds.
The best location for your milk jug seedlings is an eastern exposure with morning sun and afternoon shade. This will provide enough warmth to germinate, but avoid drying out or burning when the afternoon temperatures start to warm up. If that's not possible, you can move them around when it starts warming to be in the shade in the afternoon.
If you've tried this early sowing method, I'd love to hear about your experience!
Make This Year's Garden A Success!