Tips to rescue houseplants from the cold

Set yourself, and your houseplants up for success with these tips from Master Gardener Carlene Olsen.  Winterizing plants can be a fun and exciting way to enjoy them all year long. 

Keeping insects at bay

Aphids, mealybugs, white flies and other pests aren’t usually a problem when potted indoor plants are outside, but they can quickly turn into a major infestation during the winter if they are brought inside with the plants. Some experts recommend bathing or soaking plants in a bucket of water with mild dishwashing soap before bringing them inside. If your plants are too big for the bucket treatment, spray them with water to remove outdoor dust and soft-bodied insects from the leaves. Next, wash the top and undersides of the leaves with water and dishwashing soap, and then rinse with water. Wash the outside of the pots to remove dirt and any unwanted pests that might be present. It is important that the soapy water also gets into the soil as it will help to kill any pests living there, too. You can purchase a premixed neem oil spray or purchase neem oil and make your own mixture. Typically, a teaspoon of neem oil mixed with a quart of water and a few drops of dish soap will help the oil emulsify. Spray this mix on the leaves and soil. It’s gentle on plants but tough on pests. You may want to spot test on a small area of the plant before applying. Also, avoid applying to any stressed or unhealthy plants. Once inside, check them with each watering for any sign of infestation and, if spotted, treat them with your neem spray until the problem is resolved.

Repotting for success

If you've been meaning to repot any plants, fall is your last chance before plant growth slows in winter. When repotting, check for dead or rotten roots, use fresh soil mix, and water plants thoroughly afterward. Your plants will need less water, and you should stop fertilizing in the fall but start back up in late winter or early spring. Take a few weeks to gradually adjust your plants to lower light by moving them into shadier conditions for a few hours each day. Bring plants in for winter before night temps hit below 50 degrees for most tropical houseplants and below 40 degrees for most succulents. Just like hardening off your new seedlings, your houseplants may undergo shock if abruptly brought from outdoor conditions to indoors. This may result in yellow leaves, wilt, dieback or even death.

Sunlight and Heat

Many of our houseplants originate from tropical regions where the tree canopy constantly filters sunlight. However, some plants, especially those native to South Africa and Australia, need a lot of sunshine to thrive indoors. Some examples of plants that like direct sunlight are jade plants, hibiscus, papyrus, croton and African milk tree. Place them in a south- or west-facing window. If your space is regularly below 60°F at night, take steps to retain heat like sealing cracks around windows and doors or using energy-efficient window coverings. You can also turn on the heat but take care not to toast your houseplants with too much hot, dry air. Geraniums, coleus, begonias and impatiens can be propagated by using cuttings to generate a new crop for next summer. Cuttings should be approximately 4 inches long and be taken from vigorous, healthy plants. Remove the leaves from the bottom portions of cuttings. Lightweight growing mediums like vermiculite are best for developing new roots. Provide a consistent water supply. Use a porous clay pot, corked in the center, on a dish that you add water to. I purchase the Prince Tut papyrus plants every spring for my thriller in my deck pots. This year I will try to propagate and keep inside as a house plant and repot next spring. It is fun to experiment with keeping plants overwinter to replant in the spring. For more information on caring for houseplants over winter, please visit Managing insects on indoor plants | UMN Extension