Outdoor container gardens are typically planted with annual plant species that are discarded come late fall and replaced with new plants each spring. However, many perennial plants such as roses, peonies, and hibiscus can also be grown outdoors in containers and kept alive through winter. That being said, protecting your potted plants throughout the cold winter is not always easy—even species that are technically cold-hardy in your area can experience harsh conditions they can't tolerate and many species that survive the winter just fine when planted in the ground can die in containers without the proper care.
As a general rule of thumb, a perennial plant should be rated for two cold hardiness zones colder than your climate to be dependably hardy in a container through winter. For example, a gardener in USDA cold hardiness zone 5 can expect perennials rated for zone 3 or colder to survive the winter in containers.
While some plants can survive light frosts, others will die 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.
Whatever measures you take to protect your potted perennials for winter should be implemented a week or so before the first frost is expected. Follow these easy steps to safeguard your container plants and ensure they make it through winter healthy and unscathed.
Equipment / Tools
- Shovel or trowel
- Insulating materials (such as mulch, straw, or leaves)
- Chicken wire or hardware cloth (if building silo)
- Stakes (if building a silo)
Inspect Your Container
Make sure your container is strong enough to last through the winter. The more porous a container is, the more likely it will be to crack. Fiberglass and plastic containers are usually resilient enough to tolerate freezing, while certain natural materials, such as untreated terra cotta, readily absorb water. When water freezes and expands, it can crack the container. If your plant is not currently in a container that can withstand frozen temperatures, consider repotting it before continuing.
Dig a Hole
Choose a relatively sheltered location in your garden or elsewhere on your lawn to house your plants for winter. Dig a hole that's slightly deeper than the container you wish to bury, allowing for just a bit of extra room around the edges of the container as well.
Layer in Gravel
Spreading a layer of gravel at the base of your hole will facilitate drainage in the spring as the soil in the pot eventually thaws. The loose soil of potted plants typically defrosts a little faster than surrounding garden soil, which means drainage can be an issue.
Put the Pot into the Hole and Backfill With Soil
Place your container into the hole atop the gravel, then spread a layer of garden soil over the top of the pot. Ideally, the rim of the pot should be slightly lower than the surrounding ground, allowing you to cover it completely without creating a lump in the surface of your garden. If you need to, mark the top of the soil so you know where to find your plant come spring.
Winterize the Plant
Plan to winterize your buried container 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 might also involve spreading leaves, straw, or compost over the spot where you've buried the pot.
Unearth Your Plant in Spring
When spring comes, lift your potted plant from the soil as soon as the ground thaws and new growth begins to appear (you don't want a buried plant to soak in water from spring rain any longer than necessary). Move the pot back to the location where it resides for the warmer months.
Sheltering Potted Plants for Winter
It's not necessarily low temperatures that kill plants over the winter, but rather the rapid swings between warmer and cooler temperatures that can stress the plant by thawing and freezing cycles. If you can provide shelter to help insulate your container plants from temperature swings, your potted perennials will stand a much better chance of survival. There are several ways to do this.
Cluster Your Potted Plants
Cluster several potted plants together in a sheltered part of your property, such as up against the house. There, they'll be protected from any winds that can rapidly drop temperatures and will enjoy some heat radiating from the house. Choose a spot that is relatively shady—contrary to the belief that sunny is best, placing your potted perennial in a bright location can exacerbate any thaw-freeze cycle over the winter. Thus, it's typically best to position plants in a location where the temperature swings will be less dramatic.
Provide Additional Shelter
In addition to clustering your plants together, you can also cover the pots with a tarp, straw, or another insulating material. Doing so will moderate the temperature swings and increase the likelihood of your perennials surviving the winter.
Build Insulating Silos
Some gardeners opt to build insulated silos around their potted plants to protect them from damaging winds, especially in the case of more delicate varietals like potted roses and other shrubs. To do so, use chicken wire or metal hardware cloth and stakes to form an enclosure around the plant. Fill the silo with loose leaves or straw to keep your plan cozy. Another option to protect young trees and shrubs from strong winter winds is to wrap burlap around the outside of the silo, leaving a slight gap on the southwest exposure to allow heat to escape.
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 through winter. However, 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 during the winter months when the sun is low in the sky and the days are short. Additionally, indoor conditions are often very dry in the winter, and many perennials need humidity—if your house lacks moisture, invest in a humidifier if you plan to bring any container plants indoors.