Using the Winter Sowing Technique with Vegetables

I’m always looking for ways to stretch my growing season up here in Minnesota, and winter sowing lets me get a jump on starting seedlings—without extra lights! The trick is in choosing the right seeds to start and when!

Late in January, you can find me thawing out some soil to plant seeds. Not seeds to grow under lights just yet, though; I send these earliest planted seeds out into the elements. This is the art of winter sowing! And of course I wanted to share what I’ve learned over the last few years.

Before we get crafting the weird little mini greenhouses that make winter sowing feel sort of like a pre-school art project, let’s go over the basics.

What is Winter Sowing?

Winter sowing is a way to work with Mother Nature to grow plants from seed. You plant seeds in a container and set them outside. They sprout in the containers and are ready to plant out into your garden from there. Trudi Greissle Davidoff was the first to write about the process of winter sowing.

The concept started by mimicking nature with seeds that need to be cold stratified, meaning the seeds must spend time in the cold (either outdoors or in a refrigerator/freezer) for a certain number of days. Most also need to go through a freezing/thawing process to help weaken and break down their seed coats, breaking the seeds out of dormancy and preparing them for germination. Planting seeds that need to be cold stratified inside a container gives you the best of both worlds. They will still be in nature (freezing, thawing), but you will also end up with a seedling that you can keep an eye on and transplant much easier.

When planting annual vegetable seeds, they obviously don’t require a stratification. But the bonuses include:

*Earlier seedlings
*No hardening off
*Stronger plants
*No extra equipment

Simple + Eco Friendly

This process does not require any extra inputs to start seeds a little earlier. I will say that up in Minnesota (Zone 4) we won’t get a full harvest from our peppers, eggplant, or tomatoes this way. However, there are quite a few plants which work wonderfully using this method.

You will most likely be reusing a plastic container. Not having to buy ‘extras’ is something to take into consideration when thinking about the costs of grow lights, heat pads, fans, and the energy to run them all. Those can add up to a big investment and a bit of an energy drain if you aren’t savvy about seed starting.

Making Your Winter Sowing
Mini Greenhouse Jug

I have posted 3 videos of the process on my YouTube for you visual learners!
* Winter Sowing Introduction
* Making and planting your Mini Greenhouse
* Placing your Mini Greenhouse Outside

Winter Sowing Vegetable Seeds

This process has mostly been used with native plants, as this gives native seeds the needed chill period (cold stratification) to germinate at the right time. There are some great basic guides about doing this with Native plants already out there.

In this article, I’ll share my findings about starting annual vegetables in winter sowing containers. We’re basically creating mini Greenhouses! As I’m always interested in trying new ways to garden, I dove into this years ago. Over the years I’ve trialed a few different varieties of cool weather vegetable crops a few different ways.

• out in the open
• under row cover
• inside my cold frame

Building on Elliot Coleman’s (Four Season Farm) writing that “The double layer moves the plants 1,000 miles to the south,” I wanted to see if growing under double ‘layers’ of protection translated well to this situation. In addition, I wanted to see if this really did anything to increase the growth rate, etc. on the spring side of seed starting rather than extending the harvest season.

I started with some of my standard cool weather crops. Overall, I got great results and so much valuable information to move forward.

Timing the Seed Starting

I’m a Minnesota Zone 4 gardener. We have pent-up gardening energy to burn in the late winter/early spring. So let’s funnel that into starting our best gardens yet!

The last frost dates in my growing area range from mid-April to early May. Based on these dates and overall germination temperature requirements (see chart below), I have found that late February to early March works best for sowing the cool season annual vegetable seeds under double protection. You could set out winter sown containers earlier, but the above dates coincide with my indoor sowing of the same crops—and I’m all about streamlining seeding!

Vegetables Started + Results

My trials for winter sown containers out in the open proved only 7-14 days of a gain from planting directly into the soil. That may be worth it to some; to each their own. That’s what makes gardening so fun—you get to decide!

*I usually sow varieties below in Winter Sown Containers
at the end of February inside my cold frame.

Spinach – Great germination. I started all spinach in a jug in the cold frame. Transplanted into cold frame mid-March; those transplants took well. Transplanted out the rest of the spinach into open ground by peas mid-April. Picture of spinach in cold frame on April 25 looking great after transplanting. My first real harvest May 8. The star of my winter sowing trials.

Beets – Great germination. I was late to transplant, but grew to better sized bulbs than those I started inside a few weeks earlier.

Bok Choi – Decent germination, super tough plants that are harvestable before most insect pests have even shown up in the garden.

Romaine (Winter Density) – Great germination, good transplanting. Got a few delicious early outer leaf harvests, but then it evened out over the course of the harvesting season.

Tatsoi – Great germination and even though transplanted later, did really well. We harvested as baby crop.

Broccoli – Decent germination rate. I was late to transplant, but were stronger plants than my indoor-sown Belstar Broccoli plants. Similar harvest dates and sizes.

Kale – Good germination and transplant, but not much earlier (or anything else noticeable) to harvest. Sowed both Scarlet and Dwarf Scotch Curly.

Minimum Soil Temps for Germination

35°– 45°F: Lettuce, Spinach

40°-50°F: Beets, Parsley, Kale, Broccoli, Leeks, Onions, Kohlrabi

45°-55°F: Cauliflower, Pak Choi, Tatsoi,

55°-65°F: Cabbage, Swiss Chard

60°F: Celery, Tomatoes

*These temps are different from optimal germination temps, which tend to be 10-20°F higher. For a full chart check out: Harvest to Table.

Looking Forward

What will I be adding this year? More winter-sown herbs, a few flower trials, and a second set of outdoor-sown brassicas (my favorite cool weather crops). I am also eager to see if there are any differences to starting winter-sown jugs in a greenhouse vs. a cold frame. Plant nerds unite!!

My Winter Sowing Schedule

Late February
Spinach, Lettuces, Beets, Cabbages, Broccoli, Kale, Brussels Sprouts, Onions

Mid-March
Thyme, Salvias, Oregano, Cilantro, Parsley, Basil

Mid-April
Cosmos, Zinnia, Marigolds, 2^nd sowing of  Lettuce +  Bok Choy

So, have I inspired you to try this form of sowing seeds? I’ll be keeping up with sharing my winter sowing adventures on my stories on my Instagram and Facebook social media accounts. I hope you follow along with us too!

Love Digging in – especially in January!
Michelle