Here’s when you need to bring your tropical plants indoors and other winter plant tips

Picture of Paul Cappiello Ph.D.

Paul Cappiello Ph.D.

Yew Dell Botanical Gardens Executive Director

Ok, you’ve gotten lucky so far. Despite a few evenings threatening a light frost, you’ve skated by with your potted tropical plants out on the porch. Maybe you slid them in the garage or tucked them behind the AC compressor, up next to the house. Maybe you covered them with bed sheets, old tablecloths or the painter’s tarp that’s been hanging around in the basement. But one way or another you’ve pushed the garden and weather gods to their limits. It’s time to move those plants inside.

Using nice old potted plants around the garden during the growing season is a time-honored tradition. They immediately say to visitors, non-gardeners and gardeners alike, that you take the time to nurture, coddle, and generally obsess over these plants for no other reason than you care about the atmosphere they create in the garden. Their mere existence means you have a certain commitment to creating that atmosphere for you and your garden guests. But as anyone who has inherited grandma’s gardenia and kept it going for more than a single growing season knows, it is a labor of love.

What is the difference between tropical and temperate plants?

We tend to think of plants as falling into two categories. Tropical plants, to some, are those shiny-leafed things that you see in bank lobbies, shopping malls and hotel reception areas. You know they’re tropical because they, well, look tropical. We all know an oak tree isn’t tropical. And we know that grandma’s jade plant is. The problem is that, as with most things in nature, it’s not that simple.

Truly tropical plants are those that hail from areas with no frost or freeze in their annual cycle. Some have a hard time handling exposure to anything below about 55 degrees. Others that we think of as tropical are fine with an occasional chilly night as long as there aren’t too many of them in a row and as long as it doesn’t actually freeze. The Boston fern (Nephrolepis exaltata ‘Bostoniana’) you have growing in a hanging basket on the porch wants to be inside for the winter. It’s tropical.

Most temperate region plants, most of what we in the middle latitudes grow as year-round garden plants, not only tolerate below-freezing temperatures during winter. They actually require the cold of winter in order to successfully complete their annual cycle.

Temperate region plants go through an annual dormancy cycle that allows them to survive sub-freezing temps. The fall foliage color we’re enjoying this week is part of the process of deciduous plants preparing to shed their leaves in preparation for winter conditions. Those temperate region plants that are evergreen (pines, spruce, boxwood and holly) and don’t lose their leaves for winter ― they don’t shed their leaves but cease growing for the winter and make some internal changes in their biochemistry to allow them to endure winter’s worst.

How much sunlight do tropical plants need in winter?

The first thing you need to understand about your indoor environment is that no matter how much you’ve spent on your sunroom, no matter how much you used celestial navigation to make sure its windows face due south, and no matter what space-age technology windows you paid for to give your plants the very best of the best, your house is way, way darker than you think. Your plants will have to adjust.

Plants of all types constantly work to balance the leaf area they produce and maintain with the amount of sunlight they can harvest. Too many leaves for the amount of available sun and you end up with yellowing and dropping, first of the older leaves and then the younger. Some tropicals respond to their new, indoor environment by dropping a few older leaves as their light balance adjustment. Others see their new environment as a tremendous shock and simply drop all their leaves. They then put out a new crop of leaves in better balance with their surroundings. If you’ve ever brought a ficus tree (Ficus benjamina) in from outside and had it summarily drop every last leaf, you know what a shock that can be. But after the big leaf drop, they generally put out new leaves, just not as many.

How often do you need to water a tropical plant in winter?

When you take 20 degrees outside winter air and heat it up to 70 degrees in your house, the relative humidity of that air drops to just about nothing. Ever wonder why you go through some much hand moisturizer in winter? Plants put up with the same thing when you move them inside. But for the most part, the lack of humidity indoors is not a huge problem. Sure, you can move your giant gardenia in the shower with you once a week but in all reality, it’s actually not necessary. They appreciate the humidity but can get by just fine without it. As long as you manage the potting mix moisture level you’re probably in good shape.

I like to use the first knuckle technique. Push your index finger into the surface of the potting mix up to about your first knuckle. If it feels cool, you probably don’t need to water. If it feels warm, that usually means things have dried out enough that it’s time to water.

Now get out there and take those old bedsheets off the gardenia and get it inside!

This article was originally published in the Courier Journal on October 14, 2022.

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