Winter Sowing Guide
What is Winter Sowing? Winter sowing is the practice of using containers to make miniature greenhouses to plant seeds outside in the coldest months of winter. It's a way of working with nature and speeding up germination without taking up space in your house, or having extra electricity costs for heated seed starting mats and grow lights, and eliminates the need to bring plants in and out to harden them off.
A note about timing: We are located on the edge of Zone 3 and Zone 4b in central Minnesota. Our planting schedule may be slightly different than yours if you live in a different climate. As a general rule, unless your particular variety requires stratification (cold treatment), you'll want to start putting out containers once the temperature is sure to stay below freezing. For us that puts us planting cold stratifying seeds in December and January, and everything else from February until April or May. We can usually transplant to the garden in late May or early to mid-June.
Here is a basic guide to help you get started!
A note about timing: We are located on the edge of Zone 3 and Zone 4b in central Minnesota. Our planting schedule may be slightly different than yours if you live in a different climate. As a general rule, unless your particular variety requires stratification (cold treatment), you'll want to start putting out containers once the temperature is sure to stay below freezing. For us that puts us planting cold stratifying seeds in December and January, and everything else from February until April or May. We can usually transplant to the garden in late May or early to mid-June.
Here is a basic guide to help you get started!
Part One - Getting the Containers Prepared
What makes a good winter sowing container? You want a container that can let the sun in (don't use solid colored containers), and you want enough space for dirt and plant growth (remember, your plants will grow in these containers until your outside temperature is warm enough to transplant them into your garden). Generally, gallon milk jugs, 2-liter pop bottles, and other similarly sized containers work great. If you don't go through a lot of plastic containers, chances are you have friends, family members, or neighbors who do. When in a pinch, you can always contact your local coffee shop and see if they'd let you have their used/empty milk jugs.
Step One - Clean Your Containers! You will want to rinse out the containers you'll be using. Remember, they'll be sitting out for several months and you don't want any mold or odor from whatever was in the container before. We typically fill a sink or bucket with hot water, and add some vinegar. Then we put each container into the cleaning water, make sure the water fills the container, swish it around, and pour it back into the sink or bucket. If the water gets cold or gross, drain it and refill with hot water and vinegar. Set the containers aside to drain/dry. Recycle or repurpose the lids - you won't be needing them for winter sowing.
Step Two - Cut Them Almost In Half. You can use scissors, a Dremel, or a soldering iron to cut most containers. You don't want them cut completely in half, so be sure to leave at least 1/2" connected as a hinge! For milk jugs I usually leave the handle as the connection point. Where you cut is up to you and will often depend on what you plan on planting. If you're growing something tall, you may want to cut a little lower to provide more grow room up top. If you are growing something with deep roots, you may want your cut higher up to allow for more soil in the bottom. We typically cut gallon milk jugs just even with the bottom of the handle, which allows about 2-3" of soil.
Step Three - Drill Drainage Holes. This is important! Make sure you have plenty of drainage holes in the bottom of your container. As a safety precaution, you will also want to drill a couple holes on the sides about 1/2-1" up in case the bottom holes get clogged. How many you add will depend on how well draining you want your soil. If you drill too many holes, you may have trouble keeping your soil moist later. If you don't drill enough, your seeds and seedlings may drown or grow mold. To be safe, drill more holes than you think you need. You can always cover up holes or water more often if the water is draining too fast, but it's harder to drill more holes once you've got dirt and seeds in them. You can use a Dremel, a drill, or a soldering iron for this part.
Part Two - Planting and Closing
What seeds can I winter sow? The simple answer is almost all of them. We have successfully winter sown fruits, vegetables, berries, herbs, and flowers. If it can grow here, it can be winter sown here. Some things actually germinate better when winter sown due to the natural stratification!
Step One - Label Your Container! This is one of three labeling steps in this process. It's very important to label everything so you know what is growing in each container. This is your first label. Use a permanent marker to write the variety name on the plastic container. We typically write it several times in different places. The sun will fade some of your labels, so it's important to have multiple labels just in case. Write it once toward the top so it's easy to see when looking at your containers, and again on the side near the bottom, where it may be more protected from the sun while under the snow. Sometimes we will also write the variety name on the bottom.
Step Two - Get Your Soil Ready! First, make sure you start with a good soil. Don't use the cheap stuff, it will turn hard and you will have lower germination and less success. Organic is always a good option. We used Organic Miracle Grow our first year winter sowing, and have since switched to ProMix (also organic) because it is available year-round and is more affordable in our area. You will want your soil to be moist. Some people put it in the container and then moisten until it drains out the bottom, but I have found it much easier to have a big bucket of soil and mix it with water in batches and then add the pre-moistened soil to my containers. You want your soil to be fully moist, but not swampy. You should be able to pick it up without it dropping globs between your fingers, but if you gently squeeze it you should get plenty of water out of it. Add 2-3 inches of soil to the bottom of your container. You don't want it packed down, but you don't want big air pockets either.
Be aware that your container is likely to drain water out the bottom. This is a good thing - it means your soil has enough water in it. If your container does not drip at all, it's a sign you need to add more water.
Be aware that your container is likely to drain water out the bottom. This is a good thing - it means your soil has enough water in it. If your container does not drip at all, it's a sign you need to add more water.
Step Three - Plant Your Seeds! You won't need to follow the packet instructions on spacing because you will be transplanting them into your garden (or other containers) later. We easily fit six or eight tomato seedlings in a one gallon milk jug, and other people plant even more heavily than that. Follow the directions for depth of planting, but don't worry about spacing.
Step Four - Add Another Label. Yes, it sounds redundant, but I can't tell you how many times this inside label has saved us from not knowing what we were growing! We can also then use this plastic plant label when we transplant. We use plastic plant labels and permanent markers. Write on both sides so that you won't have to worry about sun fading as much. Do not use wooden labels as they will get wet and start to fall apart and you won't be able to read them after months in wet dirt outside. We have heard of people using cut up plastic blinds as plant labels. You can always make your own, but keep in mind materials and how long these labels have to last in wet conditions.
Step Five - Close It Up. Your seeds are tucked in, labeled, and ready to start their winter sowing journey. Close the container, and put duct tape along the seam to keep it closed. This will assure the humidity stays in the container, will keep the cold out, and will help deter would-be pests from easily accessing your seeds and seedlings.
Step Six - Label The Tape. Trust me on this, you want to label again. Write the variety name with a permanent marker on the tape you just put around your container.
Step Seven - Bring Your Containers Outside. Yes, this is the part most people find a little boggling. Bring the container full of wet soil and seeds outside... Go on. Tuck your containers into a nice sunny place in your yard. Level land is better if you have it, and make sure it's out of the way so nobody is stepping on them and your dog isn't knocking them over. If you're only doing a few containers, you might put them up on a patio table, though some people have reported losing containers to strong winds if they're up off the ground. Line them up on your deck or patio. For us northern gardeners, South-facing is best. If you are south of the equator, you'd want to put them on the North-facing side of your house.
The wet soil will freeze, and as spring comes, the soil with thaw and freeze several times. The snow and spring rains will fall in the container, that's a good thing. Leave them alone until spring.
The wet soil will freeze, and as spring comes, the soil with thaw and freeze several times. The snow and spring rains will fall in the container, that's a good thing. Leave them alone until spring.
Part Three - Transplanting
As the weather warms up, you'll start seeing sprouts in your containers. The anticipation and excitement gets most gardeners giddy. You can check in on your containers every day if you want, just peek in through the open top! You want to see condensation on warm days. If your soil starts to dry out, you can either gently spray water in through the top hole, or fill a shallow container with water and set your winter sown container in to water from the bottom. Keep your containers moist but not sopping until your seeds are all germinated. You'll be amazed at how quickly your little sprouts turn into seedlings! Once they are crowding for space in the container, it should be getting warm enough to start working in your garden. If you are comfortable outside wearing a light sweatshirt (without a jacket or coat), you can consider opening up the containers with cold-hardy varieties (cauliflower for example). Make sure you close the containers if you're expecting to get cold weather again. Do not open the containers with warm-loving plants (tomatoes, peppers, eggplant, melons, etc.) until your ambient air temperature is within their preferred range (typically no less than 65-degrees for a low temp). You can open the containers by removing the duct tape. Just be sure to close them again if you get a particularly cold day in the forecast.
As soon as you can work your soil, you could be transplanting your hardy varieties (broccoli, cauliflower, beets, radishes, cabbage, etc.). Wait until the risk of frost has gone before transplanting out the cold-sensitive varieties. It's much easier to close a lid than try to cover them once they're out in the garden.
As with all transplants, prep your garden bed ahead of time. Add your organic fertilizer, worm castings, and epsom salt, water well, and then put your new plants into the ground. Water again once planted. Water daily for the first week at least. I saw the best tomato growth when I watered every day or two throughout the entire season (except when it rained of course). We have well draining soil, ample all-natural organic bunny manure fertilizer, and full sun for our tomato garden.
Be careful when pulling your plants out of the plastic containers. You may find it easier to carefully tip the entire container out into your hand and then pull apart individual plants. For some varieties it may be easier to just cut a chunk of the soil and transplant a block of seedlings rather than individual plants. Tomatoes should be planted one at a time, while most root vegetables and ground-cover flowers will do better with the chunk method.
((Photos to come in spring 2018))
As soon as you can work your soil, you could be transplanting your hardy varieties (broccoli, cauliflower, beets, radishes, cabbage, etc.). Wait until the risk of frost has gone before transplanting out the cold-sensitive varieties. It's much easier to close a lid than try to cover them once they're out in the garden.
As with all transplants, prep your garden bed ahead of time. Add your organic fertilizer, worm castings, and epsom salt, water well, and then put your new plants into the ground. Water again once planted. Water daily for the first week at least. I saw the best tomato growth when I watered every day or two throughout the entire season (except when it rained of course). We have well draining soil, ample all-natural organic bunny manure fertilizer, and full sun for our tomato garden.
Be careful when pulling your plants out of the plastic containers. You may find it easier to carefully tip the entire container out into your hand and then pull apart individual plants. For some varieties it may be easier to just cut a chunk of the soil and transplant a block of seedlings rather than individual plants. Tomatoes should be planted one at a time, while most root vegetables and ground-cover flowers will do better with the chunk method.
((Photos to come in spring 2018))
Part Four - Clean Up
You can choose to save your winter sowing containers to use again next year, or you can recycle them and start over next time. It really depends on your preferrance. Would you prefer to store and re-sanitize the same containers, or would you prefer to sanitize, cut, and drill new containers and not have to store them all summer? If you are growing different varieties you can always write over the faded labels, or cross out any labels that didn't fade if you choose to re-use containers. Our suggestion is to use your garden hose to spray out extra dirt before storing them. This makes future sanitizing a little easier.
Still have questions? Contact us! We would love to help you get started with winter sowing!