A Beginner's Guide to Overwintering Your Vegetable & Herb Garden

Growing vegetables in the winter may seem impossible where you live. But, with a bit of planning, you can extend your harvest and enjoy sweet, crunchy vegetables through the cooler months.

So, what is overwintering, and how can you implement the practice of overwintering vegetables in your home garden?

Overwintering can look a little different for different kinds of plants. For some plants like dahlias, overwintering involves digging up the roots and storing them for spring planting. For other plants, such as coleus, it means bringing them indoors and enjoying them as houseplants. 

Overwintering vegetables means leaving them in the ground, protecting them as needed, and harvesting them for as long as possible. 

Overwintering herbs can include leaving them in the ground and bringing them indoors to continue growing. 

When sunlight falls below 10 hours a day, plant growth stops and most perennials go through a dormant period. It may not seem like the plants are doing much above the ground during this resting time, but their roots are storing up carbohydrates. When spring comes, they will use all that energy to shoot up vigorous new growth. During this dormant period, plants slow down their respiration and photosynthesis, so they don’t need as much sunlight and water. They also don’t need fertilizer. 

So while plants don’t need much help from us to survive their dormant period, there are some ways to overwinter plants and extend your garden season. We’ll cover the basics of overwintering herbs inside as well as helping the cold-hardy vegetables survive outside.

The USDA Plant Hardiness Zone Map will tell you the average temperature range in your area. Knowing your zone will help you know which plants can stay outside, which will need extra care, which plants need to come inside, and which ones need to say goodbye.

In zones where freezing temperatures are rare, overwintering may only require a warm fleece blanket over tender plants on the coldest nights. During the day, the blanket is removed, and the plant gets all the sunshine and warmth it needs.

When the temperatures start dropping, those heat-loving vegetables like tomatoes and peppers are done. You can extend their season by covering them on cold nights, especially when it is followed by another few weeks of warm daytime temperatures. This will allow time for the fruit already on to ripen, but the plant won’t be setting new blossoms. Eventually, they will stop growing, and it’s time to pull them out.

But what about all those cold-hardy vegetables? This is where the fun of overwintering vegetables is found.

Low tunnels are an easy way to make a microclimate that creates the right growing conditions for cold weather crops. Tunnels can be made from PVC or wire bent over rows or raised garden beds. Then, if there is going to be a light frost, you can place blankets, sheets, or thick plastic over the top and secure it with stakes or sandbags. Tunnels can make the air inside up to 10 degrees warmer, depending on the covering. The coverings can be removed or vented as needed to keep plants from getting too hot during the day. Tunnels can extend the growing season and overwinter cold weather crops while protecting them from freezing winds.

Water deeply before it freezes outside. Wet soil will retain heat better than dry soil. Mulching also adds heat and retains water, which can help keep roots warm when applied before a hard freeze.

Consider what you want to accomplish. Are you bringing plants inside to keep them from freezing? Do you want to bring herbs inside to continue using them?

Most vegetables will not fruit indoors in the cold. They may survive, but they won’t flower or produce fruit. 

In some climates, perennial herbs such as lavender, thyme, and sage will survive cold months outdoors. However, plants that need to be protected from freezing temperatures will need to come inside.  

Plants such as chives, and  alpine strawberries will die back after a freeze. They can be covered with straw and they will regrow in spring.

Plants such as arugula, broccoli, brussels sprouts, kale, spinach, carrots, turnips, and even beets, do well far into the winter. When they are overwintered properly, come March, you may even see your broccoli and kale sprouting again.

The cold-hardy vegetables can take a frost or two. But when temperatures drop below 25 degrees, they need extra precautions. This is where poly tunnels, mulching, and covering with straw can help.

Since fall temperatures can vary widely, you can bring plants in on cold nights and set them back outside when it is warm. This also helps them slowly get used to being indoors. If you are going to bring herbs indoors, do so before the first frost to protect them from damage.

• When bringing them inside, inspect plants carefully and remove any diseased or yellowing leaves. Wipe off leaves to make sure you’re not bringing in pests.

• Herbs that have been growing in containers are natural choices for moving indoors. Digging them up can disrupt the roots, and they may not survive. 

• Herbs need at least 4 hours of direct sun. Low humidity indoors is hard on plants - putting the pots on trays of pebbles with water can increase the humidity level around the plants.

• Maintaining a consistent temperature indoors is important in overwintering. The temperature needs to keep plants from freezing but not be warm enough for them to start growing. Usually, between 45 and 60 degrees is a nice comfortable temperature for plants to take a cool winter nap.

Whether you’re bringing plants inside or tending to them outside, overwintering your vegetables and herbs can be a satisfying way to stay to keep gardening and harvesting as long as possible.