Winter is here and your outdoor potted plants can’t be ignored. The key to keeping them healthy through the wind, cold, and snow is to protect the roots from the quick fluctuation of temperatures. This is true for plants that have been deemed hardy to your particular zone. That’s because the roots of plants growing in a pot or container are exposed to ambient temperatures while roots of plants grown in the ground are surrounded by dirt that has a constant temperature of 55°F regardless of the season or the above ground air temperature.
Although the top portion of potted plants goes dormant, the roots do not. For example, the American Holly is hardy in zone 5 of the USDA Hardiness Plant Zone Map and the top of this plant survives temperatures down to about -20°F. Yet immature roots of this plant can’t survive temperatures of 23°F and its mature roots can withstand a temperature as low as 9°F. If planted in the ground its roots would be insulated and the plant can survive average minimum temperatures of -10°F down to -20°F. However, if planted in a container and left outdoors, root damage begins at 23°F.
Protecting Potted Plants With Delicate Root Systems
Three ways to protect potted plants with delicate root systems include:
- Preventing exposure to the freeze/thaw cycle.
- Selecting the proper size pot in which the plant can grow.
- Installing the plant in a container as early as possible.
Roots can suffer significant harm due to the rapid fluctuation of temperatures from cold to hot and back to cold. A condition such as this could lift a plant out of a pot.
A container holding a plant and sitting on pavement can do well as long as the sun is warming the pavement. At night, temperatures drop. The fluctuation of temperature causes the plant to freeze and thaw.
The size of the pot is important to protecting plant roots. The rule of thumb is the bigger the pot, the better. Soil in a 15-gallon container insulates the roots better than a one-gallon container. The smaller container freezes faster and dries out quicker than a bigger container. It is recommended, therefore, that you select a larger pot that is 1-inch or more thick.
Plants have a greater chance of surviving the winter if their roots have had time to establish. So place them in pots sooner and choose plants that are hardy to two zones cooler than the zone in which you live.
Selecting The Proper Pot
The type of pot you select should be based on the climate in your region. Freeze and thaw tends to break untreated porous containers like terra cotta and ceramic. However, if you like the looks of terra cotta or ceramic and are determined to use it, then coat the pot with pool paint. The paint prevents moisture from getting into the porous surface and stops cracks from freezing and thawing.
Wood containers are durable depending on the type of wood and its exposure to the air.
Concrete, plastic, metal containers and other non-porous style pots are ideal for withstanding the environment. However, concrete and metal containers are heavy and somewhat difficult to move once they’re placed.
Foam or resin pots are a good alternative to concrete or metal, are light and come in an assortment of styles.
Plastic pots can break over time.
Be aware that plants can be top heavy in lightweight pots like foam or resin and can tumble when encountering a strong wind.
Don’t use thin-walled containers or hanging baskets because they can’t provide the protection the plant’s roots will need in winter and plants hosted in hanging baskets dry out faster than containers designed to sit on the ground.
Avoid using saucers to catch moisture under pots because collected water can freeze. Place pots on objects to assure good drainage.
Pick The Right Place For The Pot
Where you put the plant container should assure protection. Place containers on the north or east side of a house where there’s shade. A south facing location tends to have temperature variations.
Watering Potted Plants In Winter
It is essential to water potted plants in winter because there is less rainfall then. The best part of the day to water is when the temperature is above freezing. Try to water before the arrival of wind or freezing conditions.
Believe it or not, frozen water offers warmth for the roots because the frost penetrates deeper into the spaces in dry soil than in most soil where water fills the open pockets. It is suggested that even if the temperature is freezing and the pot soil feels dry, apply water to better protect the roots of the plant. This helps to ensure that the plants won’t have problems in the spring, prevents them from remaining dormant, allows them to bud properly, and ensures new growth in the spring. If the root can’t support growth, the plant dies. If the plant survives through winter, its growth may have slowed and will develop very little the following fall.
Additional Protection Tips
There are a number of things you can do to ensure protection. Most of these ideas deal with enhancing the pot’s ability to protect the plant it hosts.
Improving the pot’s insulation is probably the most important way to ensure plant protection. For example, add mulch with straw or shredded leaves. Believe it or not, snow is a good insulator.
Keep in mind that a majority of roots of potted plants appear on the outside of the root ball. Therefore, you should attempt to insulate the wall of the pot. Before installing a plant in a square pot, cover the sides of the pot with 1-inch of foam. For rounded pots, line the interior walls of the pot with Styrofoam peanuts.
Other ways to ensure that the roots of the potted plant remains warm, bury the pot in soil up to its top or insert a pot into a larger pot with thick walls or additional insulation for added protection. You can also wrap pots in burlap, bubble wrap, old blankets, or geo-textile blankets. There’s no need to cover the entire plant. Instead, focus on the roots.
It is also recommended to group a number of pots together on soil that is close to your house or wall. Place the coldest hardiest plants on the outside of the grouping and place the less hardy plants in the center. You can put straw bales on the perimeter of the grouping. Gathering the pots together increases the mass and volume of insulation and protects the pots from cold, and harsh winds.