Outdoor container gardens usually involve annual plant species that are simply discarded in the late fall and replaced with new plants in the spring. But many perennial plants, such as roses and hibiscus, also can be grown outdoors in containers and kept alive through winter. However, protecting potted plants during the winter is not easy. Even species that are technically cold-hardy in your area might experience harsh conditions they can't tolerate. Plus, many species that survive the winter just fine when planted in the ground might die in containers unless you use some special plant-protection techniques.
Equipment / Tools
- Shovel or trowel
- Insulating materials (such as mulch, straw, or leaves)
- Chicken wire (where necessary)
- Stakes (where necessary)
Burying Potted Plants for Winter
If your potted perennial is cold-hardy in your climate, you can bury its entire container in the ground for winter. It will experience the same protection from the earth as any perennials planted directly in the soil. This is perhaps the best option, provided you have the garden space.
Choose a relatively sheltered location. Then, dig a hole in the earth that is slightly deeper than the container.
Spread a layer of gravel at the bottom of the hole. This will facilitate drainage in the spring as the soil in the pot thaws. The loose soil of potted plants typically thaws a little faster than surrounding garden soil, which means drainage can be an issue.
Set the pot into the hole, and backfill with dirt around it. Spread a thin layer of garden soil over the top of the pot. Ideally, the rim of the pot should be slightly lower than the surrounding ground.
Winterize the buried plant just as you would any similar plant growing in the ground. For example, if the standard recommendation is to mulch over a particular garden perennial for winter, do so with the buried potted plant. This also can involve spreading leaves, straw, or compost over the spot where you've buried the pot.
When spring comes, lift your potted plant from the ground as soon as the ground thaws and new growth is beginning to appear. You don't want a buried plant to soak in water from spring rain any longer than is necessary. Move the pot back to the location where it resides for the warmer months.
Sheltering Potted Plants for Winter
It's not necessarily the low temperatures that kill many plants over the winter. Rather, it's the rapid swings between warmer and cooler temperatures that stress the plant by thawing and freezing it. So if you can provide shelter that helps to insulate your container from temperature swings, your potted perennial will stand a much better chance of survival. There are multiple ways to do this.
Placing your potted perennial in a sunny location can exacerbate any thaw-freeze cycle over the winter. Thus, it's typically best to position plants in a shady, sheltered location where the temperature swings will be less dramatic.
Cluster several potted plants together in a sheltered part of your property, such as against a house wall. These pots will be protected from winds that can rapidly drop temperatures, and they will enjoy some heat radiation from the house.
Consider providing additional shelter for a cluster of pots with a tarp. Or cover the pots with straw or another insulating material. You also can insulate the roots with additional soil. One option is to slip the existing pot into a larger container and fill the sides with soil or mulch. This will moderate the temperature swings and increase the likelihood of your perennials surviving the winter.
Many gardeners opt to build insulating silos around their plants, especially for potted roses and other shrubs. Use chicken wire and stakes to form the silo. Then, fill the silo with loose leaves or straw around the pot.
When to Protect Potted Plants for Winter
Whatever measures you take to protect your potted perennials for winter should be put into action a week or so before the first frost is expected. While some plants can survive light frosts, others will die for good as soon as their cells freeze.
Depending on their hardiness, some potted plants will respond to the first frost by going dormant just like garden plants do. However, as the temperature continues to drop, their roots might die unless they are protected. Thus, the best time to prepare for winter is before the deep freeze begins.
Digging and Storing Bulbs, Corms, or Tubers
If your container garden contains bulbs, corms, or tubers, one strategy is to dig up the root structures and store them for the winter in a cool, dry location. Then, replant them back into your outdoor containers the following spring. This is not always successful, as some stored bulbs rot or desiccate over the winter. Plus, you will need to know the winter conditions your plant species prefers.
Moving Potted Plants Indoors for Winter
A technique that is sometimes successful is to move potted perennials indoors for the winter. This works best with tropical perennials, such as begonias, that keep growing through the winter. Small potted fruit trees that spend the summer on a deck or patio can also live indoors for winter. But perennials that require winter dieback and a dormancy period shouldn't be brought inside.
The key is to have an indoor spot with plenty of light. This can be hard to come by in the wintertime when the sun is low in the sky and the days are short. Further complicating matters is that indoor conditions are often very dry in the winter, and many of these perennials need humidity. But if you can provide the right conditions, moving potted perennials indoors for winter is a good strategy.
Tips to Protect Potted Plants for Winter
The general rule is a perennial plant should be rated for two hardiness zones colder than your climate to be dependably hardy in a container for winter. For example, a gardener in zone 5 can expect perennials rated for zone 3 or colder to survive the winter in containers. However, by protecting your plants from the elements, you might find it possible to maintain some potted perennials that match your hardiness zone.
Make sure your container is strong enough to last through winter. The more porous a container is, the more likely it will crack. Certain pot materials, such as untreated terra cotta, readily absorb water, which will expand when frozen and crack the pot. Plastic containers are usually resilient enough to tolerate freezing.
When the ground freezes under a container, water can't escape through the bottom. In spring, the container will thaw before the ground does. And if you get a few rainy days, water will stand in the pot, either rotting the roots or turning to ice if the weather chills again. Avoid this by slightly tilting the pot until it's ready to resume its normal position for spring.