How gardeners can nurture their outdoor potted plants through winter

Perennial plants being overwintered in pots are subjected to much harsher conditions compared with those in the soil.

Because of this, they can be damaged and killed. Fortunately, there are some steps to try to get these plants through the winter and enjoy them again come spring.

Why take time to protect potted perennial plants?

So, why take the time to protect potted perennial plants? Most plants’ roots are far less cold-hardy than their above-ground parts. Usually, this isn’t an issue because the soil will insulate the roots and protect them from extreme cold temperatures. While potted plants may be in a growing media, the amount of media is small and will get much colder than soil in a landscape.

Since potted plants’ roots are exposed to colder conditions than those in the ground, it’s a good idea to look for plants that will survive in a hardiness lower than the zone they will grow in. The general rule is to select plants that will survive two zones cooler than where the plant will be growing.

For example, central Illinois is zone 5 or 6. Therefore, for that location, consider a plant that is hardy to zone 3 or 4 if planning to overwinter it outdoors in a pot.

Perennial plants in pots

Explore a few steps that are best for hardy perennials. The following guidelines do not apply to nonhardy plants such as geraniums, as those may need to be handled differently.

Before getting pots ready to overwinter, make sure the plants inside are well watered, and check throughout the winter. This is especially important for evergreens to help prevent winter burn. Even after above-ground growth has gone dormant for the year, the roots will continue to take up water. In addition to providing water to the plants, moist growing media will freeze slower than dry media, offering additional protection.

The most common way to overwinter potted perennials is by storing them indoors. Places such as an unheated garage, shed or cool/cold basement can be good locations to place potted perennials for the winter. Many perennials need a cold dormancy to properly bloom and grow, so if a garage or basement is too warm – temperatures should be between 20 and 45 degrees – consider elsewhere.

A second option is to sink containers into the ground. By placing the pots in the ground, the surrounding soil can insulate the pot, providing protection from extremely cold temperatures and temperature fluctuations. Additionally, the pots and plants can be mulched to provide additional protection. Once the danger of a hard frost has passed, the pots can be removed from their holes.

Grouping pots together in a protected location. If digging a hole in the ground isn’t an option, or the pot is too large, try grouping pots. Look for an area that doesn’t receive strong winds or too much sunlight, such as the north or east side of a building. Once the pots are clustered, mulch them heavily with straw, leaves or wood mulch. Once growth resumes in the spring, remove the mulch and return the pots to their rightful place.

And if you want to move plants indoors, here are some tips for making it a successful move.

How to bring the outdoor plants inside

To build an indoor garden, select plants to bring indoors or purchase some new plants. It’s a little late in Illinois to be moving plants from outside to indoors, but there are a few things to consider for a smooth transition.

Monitor the temperature. Move houseplants inside before night-time temperatures get below 45 degrees.

Watch out for hitchhikers. Before moving houseplants indoors, check leaves, stems and soil thoroughly for pest problems. Common pests are aphids, scale, mealybugs and spider mites. Spray any pests with insecticidal soap. Give plants a good wash with a strong spray of water to dislodge any undetected hitchhikers.

Time to acclimate. Slowly acclimate plants to lower light levels by placing them in shaded areas for a couple of weeks before the transition to indoors. This is also a good time to trim overgrown plants and remove any dead leaves.

Reduce watering and fertilizing. Plants need a period to rest from growth and flowering. During colder months the need for water and fertilizer is lower. Provide enough water so that the plants do not dry out completely.

Provide light and humidity. Bright, indirect light is necessary. Remember, photosynthesis is how the plant makes food. If an area is darker, consider adding grow lights. As heated homes typically have dry air, use a humidifier or mist plants daily to keep leaf tips from turning brown.

Once plants have been successfully transitioned indoors, the most important factor in creating a relaxing atmosphere using plants as a backdrop is you.

For more on overwintering potted plants, check out the Good Growing blog. For questions, contact a local University of Illinois Extension office.