Smart, thrifty gardeners can transform ordinary milk jugs into mini greenhouses that help seedlings thrive, even when the temperatures are chilly.
What is Winter Sowing?
Winter sowing is a fantastic way to jump ahead with hardy flowers and herbs plus cool-season crops like cabbage and salads which will germinate in their own time as the weather warms up.
This often-overlooked method creates a protected environment around the seeds to keep cold winds and pests like birds and slugs at bay. Safely cocooned inside, seeds can sprout in their own time – as and when conditions allow – and the greenhouse-like conditions will help speed along growth and give bigger, healthier seedlings.
Recycling milk jugs as seed-starting containers is cheap and convenient, but you could use any container that will allow sunlight through. Opaque containers are best avoided as seedlings will need light once they germinate. Gallon-sized jugs those are the best because they’ll give plenty of space around your seedlings.
You could also use the clear plastic clamshell boxes salads sometimes come in, or even trays with humidity domes on top – anything that traps a little bit of heat and shelters seedlings from the worst of the elements. Make sure there’s enough headroom for the seedlings to grow into as they get taller.
![Winter-sowing seeds]()
Space out seeds across the surface of the potting mix before sealing them inside the milk jug
How to Make a Milk Jug Seed-Starting Container
The bottom half of the milk jug will be filled with potting mix, while the top half will act as a greenhouse – all in one handy container! It’s a very cheap way to start seeds, and you’ll get a lot of seedlings inside so it’s super-savvy space-saving too.
The first job is to slice your milk jugs around the middle. Use a little saw or knife to make a hole in the side, then push scissors into it and start cutting. Don’t cut it all the way around though – leave a hinge at the handle end of the jug.
Next, poke several drainage holes into the bottom with a screwdriver to let water drain easily away.
What Seeds Can You Winter-Sow?
Winter sowing is great for two, distinct sets of plants: hardy flowers that actually need a period of cold to spark them into life (the technical term for this is ‘cold stratification’), and cool-season veggies, to enjoy a few weeks’ head start on direct-sown seeds. This method isn’t suitable for crops that like heat like tomatoes, peppers, beans or corn.
![Milk jugs for winter sowing]()
Seal your milk jugs with duct tape before setting them outside
Winter Sowing Flowers
Many flowers, from hardy annuals to perennials that live for many years, can be winter sown. For my productive plot I concentrate on sowing hardy, vegetable garden-friendly annual flowers like love-in-a-mist, poppies, sweet peas and calendula that will help attract beneficial bugs and perhaps, as a bonus, offer a few cut flowers. There’s a long list of hardy flowers perfect for winter sowing, but here are some of my favorites:
Annual Flowers to Winter Sow
- Bells of Ireland
- Calendula
- Cornflower (Bachelor's buttons)
- Cosmos
- Sweet William
- Nigella (Love-in-a-mist)
- Marigolds
- Pansy
- Poppies
- Snapdragon
- Sweet pea
![Labelled milk jugs for winter sowing]()
Don't forget to label your milk jugs so you know what's growing inside
Perennial Flowers to Winter Sow
- Black-Eyed Susan
- Butterfly weed
- Columbine
- Coreopsis
- Delphinium
- Echinacea
- Foxglove
- Gypsophila
- Helenium
- Hollyhock
- Joe Pye weed
- Monarda
- Scabious
- Yarrow
If you’re unsure whether something is suitable for winter sowing, look for clues in its description including terms such as: self-sowing, direct-sow, cold hardy, can withstand frost,, pre-chill, or chill before sowing. All these terms indicate the seedlings are hardy and great for sowing early like this.
![Winter-sown seedlings in milk jugs]()
The winter sowing technique is suitable for hardy flowers and cool-season veggies
Winter Sowing Vegetables
Just about any hardy, cool-season vegetable is also suitable for winter sowing, for instance:
- Arugula
- Broccoli
- Brussels sprouts
- Cabbage
- Cauliflower
- Chard
- Kale
- Kohlrabi
- Leeks
- Lettuce (and other salads)
- Onions, inc. salad onions
- Spinach
How to Winter-Sow
Okay, so let’s get sowing! First fill your prepared jugs with a pre-moistened potting mix. Any all-purpose mix is fine, and is a lot cheaper than a seed-starting mix. Just screen out any lumpy bits.
Fill almost all the way up to the top of the bottom half, and pat it all down to leave a smooth surface. Then take little pinches of seeds carefully broadcast them across the surface. Cover the seeds with a touch more of your potting mix. Water to help to settle the potting mix around the seeds, so they’re in good contact.
And then it’s on with their mini-greenhouse domes. Use duct tape to seal the top to the bottom, as it’s very tough and stay sticky even when out in the rain. Label the outside of the jugs to make it easy to quickly identify what you’ve sown. Take off any lids to let in air and a little bit of rain to keep the potting mix damp.
![Ben checking on his winter-sown seedlings]()
Seeing those seedlings pop up without any intervention from the gardener is so exciting!
Your milk jugs can now be placed into a relatively sheltered and somewhat sunny site, somewhere they won’t get flooded by saturated soil. They are quite heavy, but there’s no harm in grouping them together to make make it harder for the wind to blow them over. This will also give a bit of thermal mass to help keep them cozy – think of penguins huddling together on the ice!
If you get snow, no worries – it will help to insulate the jugs against the harshest cold. The great joy of winter sowing is that whatever the weather throws at them, they’ll still germinate and grow in their own sweet time. The seeds just seem to know when the best time to poke through is.
Check on your jugs from time to time and, if the potting mix seems a bit dry, open them up to water them, then re-seal (or just mist spray water through the top).
![Winter-sown seedlings in a milk jug]()
Winter-sown seedlings grow up sturdy and strong once conditions are right
Transplanting Winter-Sown Seedlings
Daytime temperatures inside your milk jug mini-greenhouses will be a lot warmer than outside, so your seedlings will likely poke through two to three weeks earlier than seed sown directly outside. There’s no need to harden them off (acclimatize them to outdoor conditions) – you can just transplant them to where you want them to grow immediately.
But depending on what you’re growing and the size of your seedlings, you may want to grow them on in your milk jugs for a few more weeks until they are a few inches (about 5cm) tall. If that’s the plan, remove any excess seedlings so they aren’t too crowded, leaving at least an inch (2cm) between them.
![Winter-sown seedlings in milk jugs]()
Hinge back the lids once the weather starts to warm up
As Spring approaches and the weather begins to warm, you can open up the jugs during the day. This is where that hinge comes in handy, because it means you can then re-seal it at night if the forecast is chilly – kind of like opening and closing the greenhouse door and windows! Grow the little seedlings on until you’re ready to deal with them or soil conditions are suitable.
Don’t you just love the simplicity of this method? It’s fab, right!? All of the vegetables and flowers featured today can be found in our Garden Planner, which will show you the best spacings for growing them on, and when you can expect to harvest or enjoy them in your location. You can try the Garden Planner for free – no payment details required – by taking advantage of our 7 day trial.
