Winterizing Your Houseplants & Patio Plants

November 18, 2017


Question:

What steps do you recommend as we transition our houseplants back inside and prepare patio plants for the winter?

- Dan G., Bosque Farms, Valencia County, NM

Answer:

Three weeks ago, I brought in my container patio plants that can't tolerate the cold. These included the huge spider plant that began as a cutting from my grandmother's huge spider plant, various succulents, and my prized pineapple plant that I started from a pineapple top a few years ago. Other plants, like the octopus agave, geraniums, and purple heart, are hardier so they can stay outside longer, but I brought them in last week rather than risk it. I like to bring cuttings of various favorites inside for the winter and keep them in water. That way, if we get a severe cold snap, I have some plant tissue to rely on in the spring for replanting.


This week I’ll winterize the hardy patio plants so that they can stay safely outside all winter. The two rose of Sharon shrubs—named, “Althea” and “Althea-later”—are currently confined in pots, and so far they overwinter very well each year with occasional watering and plenty of mulch. Keeping container plants watered during the winter is crucial for the survival of their root structure. If temperatures get cold enough to freeze the soil in patio plants, water between plant cells may freeze too, so the cells cannot take in water and subsequently dry out and die. When a plant cell freezes, at even lower temperatures, the water inside the cell forms ice crystals. The cell then lyses, or bursts, thereby killing the tissue.

Plants have a few tricks up their stems for avoiding death by frost. One of these methods involves the accumulation of solutes inside cells, such as sugars and salts, which decreases the freezing point of water. This concept is also used when salting an icy road to keep the water in that slushy, liquid state rather than freezing solid. Plants also produce different proteins that may act as a type of antifreeze between cells or bind water within the cells to avoid drying out. Some root dieback may not kill a whole plant, but better to be safe than sorry. Depending on the type of plant, soil type, size of pot, amount of roots, and sunny position on the patio, you may need to water only once a month in the winter. A good practice is to stick your finger in the soil and check soil moisture every few weeks.

I recommend arranging patio plants so they’re easy to remember and easy to water during the winter months. I keep a handy watering can close by. If you use a watering hose, be sure to disconnect the tap end because ice in the line may ruin the hose or, worse, the water pipe itself.

Hold off on fertilizing until temperatures start to warm up in the early spring. Fertilizers can promote growth, but the goal right now is to slow growth and encourage your patio plants to go dormant. In dormancy, they’ll conserve resources and be ready for leafing out in the spring.

Now let’s go back inside with the houseplants. When you bring them in, be sure to carefully examine under the pot rim for black widows or other bugs that you do not want indoors. White, crusty rings around the edges of pots are caused by salt build up on the pot surface or in the terracotta clay. Those plants may need to be repotted with fresh, less salty soil. I will also repot if the root ball is especially overgrown. In general, though, I save repotting for a spring chore when I want to encourage vigorous growth.

NMSU Extension Entomology Specialist and NMDA State Entomologist, Dr. Carol Sutherland, has these pointers for keeping pest populations under control on houseplants: 1) Clean the pot saucer for each plant you’re bringing indoors. 2) Check the drain hole on the bottom of each pot for obvious pests as well as for overgrown roots (time to repot?) or washed out potting medium. 3) Closely examine each plant and hand-pick obvious insects. Turn over those leaves! 4) Remove dead leaves and debris from the surface of the potting soil, where insects and their offspring might be hiding.

If you want to use a pesticide for insect control, here is Dr. Sutherland’s recommendation: “Pyrethrum—derived from certain chrysanthemums—is an irritant for many insects. Consider spraying each plant with a pyrethrin insecticide (read and follow all label instructions) a day before bringing them indoors. This treatment should send many potential hitchhikers packing, but not all. Check the label to determine if certain plants should NOT be treated with this active ingredient or a particular formulation. Those pests that are well hidden or immobile on the plant may escape detection. And those with bodies that are well protected by waxy coverings will survive most topical treatments.” So the best defense on those elusive pests is to watch for them throughout the year.

Every county in New Mexico has an NMSU Cooperative Extension Office with Extension Agents who field questions about various horticultural problems. In the winter months, these questions largely involve houseplant pests. Check back next week for more on controlling these pest populations before they spread and get gross!


Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!