Gardening Basics

The Cold, Hard Facts on Protecting Potted Plants

Tips for helping your potted plants survive winter.

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Microclimate matters: The wall serves as a windbreak and provides shade in the late afternoon.

Find the right place

A pot's location also determines how well plants are protected. Place containers on the north or east sides of the house where conditions are typically shadier. Southern exposures tend to have the greatest temperature swing.

Hardy dwarf conifers, evergreens, ornamental grasses and trees or shrubs with interesting habits or bark colors are great for adding winter interest. If possible, place pots with these plants near a window or front door where they'll be easily seen.

How to water during the winter

Because there's typically less rainfall in winter, adequately water your pots. Broadleaf and needled evergreens are particularly sensitive to desiccation. The ideal time to water is during the day when temperatures have warmed above freezing. If the forecast predicts windy or freezing conditions, try to water before these conditions occur.

"When water freezes, it gives off heat. There's a latent heat release," Hannah says. Water provides some warmth to the root zone. Frost penetrates deeper into the air spaces of dry soil than moist soil because, in moist soil, water has filled the air pockets. Hannah suggests that even if temperatures are at freezing and the pot is dry, it's important to water because it will help to better protect the plants' roots.

"When plants aren't properly overwintered, they'll have problems come spring," she says. For example, a plant may not break out of dormancy or it will have delayed bud break. Or, it may begin new growth at the start of the growing season, but if the roots can't support this growth, the plant dies. Even if container plants are able to make it through winter, they may have slowed growth, developing very little by following fall.

Group several pots together next to a wall to help insulate them and to protect them from winds that cause desiccation and freezing. Plus, proximity makes it easier to keep the containers watered. --photo courtesy of Denver Botanic Gardens

Overwintering options in the outdoors

Depending on where you live, it may be necessary to provide added protection for your pots. Here are several options for overwintering containers:

  • Group several pots together on soil and close to the house or wall. Place the cold-hardiest plants on the outskirts of the grouping with the less hardy plants in the center. Put straw bales on the periphery. Putting them together increases the mass and volume of insulation and protects them from cold, harsh winds that cause desiccation and freezing.

  • For added insulation, mulch pots with straw, mulch or shredded leaves. Snow also acts as a good insulator. An interesting idea for insulating containers would be group pots together in a preformed pond liner and fill the liner with mulch.

  • Because a majority of roots tend to be on the outside of the rootball, the only insulation for roots is the wall of the pot itself. Prior to planting, insert foam at least one inch thick around the walls of square pots to insulate roots. For rounded pots, line the container's interior walls with foam peanuts.

  • Bury pots in soil to the top of the container.

  • Remove the rootball from the container and plant in the ground. Clean the container and store indoors. Dig up the root ball next season and repot into the same or a larger container.

  • For extra insulation, add a generous layer of mulch around the base of the pot when you question the durability of the pot itself or the root hardiness of the plant inside.

  • Wrap pots in burlap, bubble wrap, old blankets or geotextile blankets. It isn't necessary to wrap the entire plant because it's the roots that need shielding. These protective coverings will help to trap heat and keep it at the root zone.

  • If low temperatures loom, cover plants with cloth, burlap or plastic at night. If you use plastic, be sure to remove the covering during the day since temperatures can heat up, causing premature bud growth. Also, when covering, avoid damaging the top part of the plants. Injury sets up the plant for cold and pest damage.

  • Insert your pot into a larger pot for added protection. This will work best if the larger pot has thick walls or added insulation.

    For USDA Zones 7 through 11, hard freezes may be infrequent to nonexistent, so adding insulation or bringing pots in for the winter may not be necessary. However, there are some chores that you should still be aware of. Due to cooler temperatures in the winter, plant growth will slow and watering may become infrequent. However, salt can build up in the soil, raising levels to toxicity. Water well to leach out the salts. Also, fertilize plants as needed.

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