The arrival of cold weather doesn’t have to mean the end of your gardening season! With a little planning and the right tools, you can extend your growing season and harvest homegrown vegetables throughout the cold months. The three main rules for a successful winter garden are:
- Choose cold-hardy varieties
- Sow in time for plants to reach maturity before the days become short
- Protect your plants from very cold temperatures.
What Should I Grow in my Winter Garden?
You can grow lots of different vegetables in your winter garden, especially root vegetables, leafy greens, and herbs.
When temperatures drop, plants produce more sugar, since it essentially acts like antifreeze to prevent tissue damage. This means root veggies are at their sweetest in the winter months! Here are some good types to plant for winter. Expand your winter vegetable repertoire with lesser known types that are hard to find in the grocery store, like parsnips, rutabagas, and turnips!
Just like root vegetables, greens become sweeter when exposed to cold. In fact, there are some who would argue that collards and kale that haven’t been frost-nipped aren’t even worth it!
- Asian greens, like bok choy, mizuna, and napa cabbage
- Mustard greens
- Brussels sprouts
Lots of herbs are cold tolerant, this isn’t an exhaustive list! Here are a few winter favorites.
- Green onions, aka bunching onions or scallions
Overwintered crops are not for winter harvest, but early spring harvest. By starting certain crops in the fall and protecting them over the winter, they have a head start as the days begin to lengthen and will produce earlier than if you started the seeds in early spring.
- Broccoli and cauliflower - if grown close to full size in fall and then protected over the winter, many broccoli and cauliflower varieties will head in early spring
- Onions - Bulbing varieties can be planted in fall, protected over the winter, and then they will bulb and size up in spring once the daylight hours lengthen, producing much earlier than spring-seeded onions.
When to Plant for Winter Harvest
While lots of delicious veggies can survive cold temperatures, even the most cold-hardy varieties won’t grow much when the daylight hours are short. Most plants stop growing when they receive less than 10 hours of sunlight per day. This is why timing is important to winter gardening.
One good rule of thumb is to check the days to maturity on your seed packet, and count that number of days backward from your area’s average first frost date. That’s a good time to sow crops for winter. Here in Asheville, NC, our average first frost date is October 23rd. So, if we want to grow Red Russian kale for our winter garden, and it takes 50 days to mature, we would want to have it planted by about the end of August. That way, the plants have time to grow to full size before the weather turns cold, and we lose too much daylight. We’ll be able to harvest from our kale patch all winter, but the plants won’t get much bigger during the coldest, darkest months.
How to Protect your Winter Garden
Even plants that can survive cold weather can suffer damage when the temperatures plummet into the 20s and lower. There are several ways to protect your winter crops, including row cover, cold frames, cloches, or a greenhouse.
Row cover is probably the simplest and most cost-effective way to protect a fairly large area of plants in the winter. It is a breathable, non-woven fabric that allows most light to pass through, insulating plants while allowing them to continue growing. It can be used directly on top of plants, or with hoops made of bent wire or PVC pipe to hold it off the plants’ leaves.
Using hoops offers the most protection, as it allows air to circulate between the plant and row cover. Whenever temperatures are above freezing, row covers should be removed, so that the plants get the most sunlight possible. In most areas, this means uncovering plants in the daytime and covering them back up at night. If handled carefully, row cover is reusable, and lightweight row cover can even pull double duty as insect protection for your spring crops.
Cold frames are basically low-built mini greenhouses covered with either greenhouse plastic or glass. If you live in an especially cold climate, having a few of these is an especially great way to have vegetables through winter. A cold frame can raise the temperature around your plants much higher above the outdoor temperature than row cover can. There are lots of plans available online to build your own for very little money and just a little time. This is a great way to recycle old windows. Because a cold frame has such a strong greenhouse effect, and can actually get much too hot for plants in sunny, warmer weather, you’ll need to monitor cold frames more closely than row cover and make sure to always open them when the weather is warm.
Traditionally, a cloche is a glass dome placed over an individual plant to keep it from freezing. Glass cloches were developed in the 17th century and used by many affluent European gardeners and small market farmers to provide fresh vegetables to homes and markets throughout the winter. With the advent of cheaper glass greenhouses, and later polyester row cover and plastic greenhouse material, the glass cloche has long since fallen out of favor, but you can get the same effect with clear plastic containers such as milk jugs or large juice bottles with the bottom cut out. Some people sprout seeds in cool weather under milk jug “cloches,” or you can use them to protect a few plants from a snap freeze in a pinch.
Greenhouse or Low Tunnel
If you have the space, and a bit more money to spend, a greenhouse is a game changer for winter gardening. Lots of different greenhouse kits are available in every size and price range. Larger, permanent greenhouses can easily run into the thousands of dollars, while some small, lightweight plastic models can be rather inexpensive (though you get what you pay for in durability).
One way to have much of the functionality of a greenhouse without the cost is to create a “low tunnel,” a series of hoops made of PVC pipe or metal conduit covered in clear greenhouse plastic. These tunnels are not typically large enough to stand up in, but cover at least a couple rows of vegetables under one structure. As with a cold frame, you’ll have to monitor a greenhouse or low tunnel closely, and make sure to vent it in warm weather so your plants don’t overheat.
Winter Gardening Tips
Now that you have the basics down, here are a few other things to keep in mind when growing for winter harvest!
Starting Seeds in Trays
Because plants for your winter garden need to be started in late summer or early fall, you may need to start your seeds in trays and then transplant them to the garden when space becomes available. When it’s time to seed long-maturing fall/winter crops like cabbage and brussels sprouts, your summer crops like tomatoes and peppers might not be done yet. Also, if you live in a warm climate, it might even be too hot out for those cool-weather varieties to thrive outdoors at the time they should ideally be sown. If so, it may be best to start them indoors in an air conditioned space, or if that isn’t an option, outdoors under light shade cloth.
Raised Beds Can Solve Wet Soil Problems
If you live in an area with wet winter weather, you might find that your garden becomes terribly soggy in the cold months, despite seemingly adequate drainage in the summer. If that’s the case, building raised beds can be a huge help. Most garden plants, and especially root crops, don’t thrive in waterlogged soil.
Winter Gardening in Containers
Large raised beds have plenty of thermal mass to prevent cold-tolerant plants from being damaged in cold weather, especially when covered, but you should be careful about growing in smaller containers during the winter. The small amount of soil in a pot with cold air moving all around it is much more susceptible to freezing than the ground. If you do have plants in pots over the winter, when you cover them make sure to drape the covering to the ground, not just over the top of the plant. This will trap more warmth and take advantage of the ground’s thermal mass. Placing jugs of water underneath row cover with your plants can also help a great deal, as they warm up in the daytime, and release heat at night.
Plant Extra Greens
As mentioned above, during the months with short days, plants will not grow much. This means that your greens won’t regenerate the same way they do in summer. Greens that you usually treat as “cut-and-come-again” may not produce a second cut for quite a long time. Even if you leave the top leaves on your kale or collard plants, they may not grow more leaves until the days start to lengthen when you’re harvesting in December and January. So, it’s a good idea to plant more of these types of greens than you would in the warm months.
Finally, if you don’t use all your garden space for winter veggies, plant cover crops on any unplanted areas. Cover crops protect soil and prevent erosion, while feeding your soil microbes and adding organic matter when you mow them in spring. Overwintering mix, Austrian Winter Pea, Winter Rye, Oats, and Crimson Clover are good options. Learn more about cover cropping on our blog.
Hopefully now you feel inspired to keep your gardening season going through the cold months! If you want to dig deeper into season extension techniques, check out the book Growing Under Cover for lots of in-depth knowledge about how to manage protective structures for maximum productivity in your garden.