Garden Update: Winter Care of Houseplants

By Kathleen Cue, Nebraska Extension Educator in Dodge County (Week of November 22, 2021)

If you grow your own fresh air, you appreciate the liveliness houseplants bring to the indoors during the long winter months. On days when I’m feeling blue, nothing lifts my spirits like taking care of my houseplants. Removing dead leaves, looking for any insect pests that I missed when bringing them indoors last fall, pinching off leggy stems for rooting later, checking soil levels, setting aside plants that require further attention, and admiring the handsome plants are just some of the tasks I look forward to. If leafy plants aren’t your thing, consider growing one of the hugely popular succulents now found in garden centers and online.  They offer the ease of growing cacti without all the thorns that make them user-unfriendly.

Unless you have a greenhouse or grow lights, keeping houseplants at their finest during the winter months can be a challenge. With sunlight intensity and duration at a low point, even the best window in the house can keep plant growth to a minimum. Give plants a quarter turn each time you water to keep plants from leaning and getting top heavy. Pinch off stems that have gotten leggy to keep plants looking good and place the cuttings in water for rooting. These can be potted up to give away as gifts or used to dress up outdoor containers in spring.

With reduced growth during the winter months, a houseplant’s need for nutrients drops. Unless plants have supplemental grow lights, continuing to fertilize during the winter months risks the buildup of fertilizer salts in potting soil, reaching critical levels that can kill plants. For houseplants in the window, fertilization should take place March through October, when sunlight intensity and duration promotes plant growth and vigor.

Snow melt water (allowing it to come to room temperature before using), rainwater, and water saved from the AC unit last summer are great for houseplants. Water from these sources have low amounts of minerals that make water hard but do contain trace elements beneficial to plants.  Well water and tap water are OK to use but have lots of minerals that can leave deposits on the soil surface. Water-softened water is harmful to houseplants and should not be used at all. The best way to water houseplants is from the top down, allowing excess water to drain into the catch dish below.  Allow plants to remain in the excess water for about an hour before emptying the catch dish. The method of watering houseplants known as wicking, along with leaving drained water in catch dishes, deposits minerals and salts on soil surfaces as water evaporates. Water temperature plays a huge role in root activity, so make sure water is brought to room temperature before it is used.  Never place ice cubes on the soil surface to water plants. Ice water is just above freezing and extremely injurious to plant roots.

Misting is a great way to provide humidity around houseplants—for about 10 minutes. Once plant foliage is dry, it’s back to dry air. Unless you’re willing to stand there misting your plants, it will be easier to group houseplants together, so they can bask in the humidity from their fellow plant’s evapotranspiration. Another technique to create humidity around plants is to set up a pebble tray. A shallow tray, wider than the plant’s foliage, is filled with pebbles and enough water to just cover the pebbles. Pots are placed on the pebble layer, not directly in the water. As water evaporates, voila, humidity for plants!

Pest Management
There were several hitchhikers that came in with my houseplants when moved inside. A Japanese beetle, more than several boxelder bugs, lots of fungus gnats, and a few ladybugs rounded out the mix. The vacuum cleaner made short clean-up of these visitors.  It’s the hard-to-see hitchhikers that garner more concern. Aphids, spider mites, scale, mealybugs, and whiteflies are major pests of houseplants, but they are tiny, sometimes requiring a hand lens to see them. These pests can take an otherwise healthy plant close to death in just a few months, especially when there are no insect predators to feed on them. An insecticidal soap kills most of these pests. Spray plants on a weekly basis until no more insects are seen. With scale and mealybugs, ridding plants of these species is time-consuming and has little success in long term results. Discard plants that are heavily infested. For plants with sentimental value, do a twice-weekly clean up using cotton swabs dipped in rubbing alcohol.  Always keep new plants isolated from your other houseplants for a few weeks to make sure nothing is inadvertently spread to healthy plants.

Setting Houseplants Outside
In spring, when nighttime and daytime temperatures have reached 55° F and higher, houseplants can be moved outside to take advantage of the weather. Because they are weaklings from their protected time indoors, plants should be acclimated first. Start by putting them beneath the shade of a tree or a porch, out of any direct sun, wind, or precipitation. Every few days, move plants to a more exposed place, eventually moving them to a full sun location.  Once plants are hardened off, they can be placed in their permanent summer location.

When you grow houseplants, you’re benefitting you and your family’s physical and psychological health. So… grow your own fresh air!