Well, are the cooler temperatures here to stay? Seems like it. I guess we’ll find out. But one thing we know for sure is that the cooler temperatures are going to affect our plants. Some of our plants will just go dormant for the winter but for others, the colder temperatures will signal us that they are approaching the end of their lifespan. So, we have some decisions to make. 

The decisions we have to make at least partially revolve around the preferred growing zone for those plants. For some of you, growing zones is old hat but for others, you might be saying “growing zones?” So, let’s talk a bit about growing zones. 

The United States is divided into various growing zones as determined by the USDA. Average temperatures determine the delineation of the various zones. This is useful information to gardeners because plants perform best and survive in their appropriate growing zone. Tulsa is in growing zone 7B. The USDA says that the average winter low temperatures in zone 7B are between 5 and 10 degrees. This doesn’t mean that it won’t get colder, it’s just an indicator of an average low temperature. 

We all know it can get colder which can really mess with some of our plants that are rated for zone 7 or higher… higher numbered zones have warmer average low temperatures. When these colder spells happen, we can lose a lot of plants. For an example, think of all the crapemyrtles we lost a few years ago in a cold snap. We lost them because we are at the upper edge of where you can grow crapemyrtles. So, dipping down into the negative temperatures for a few days can had an effect on the crapemyrtles, among others. 

If we’ve made good purchasing decisions for our plants by selecting zone appropriate plants, we should be fine…on average. However, most of us have some plants, likely in pots that are not rated to survive our summers. Tropical hibiscus would be an example.

Tropical hibiscus plants love our hot, humid summers, but winter will take them out. So, if you are wanting to keep your tropical hibiscus alive, you are going to need to put it in a protected area such as the garage for the winter.

I have done this for several years with our tropical hibiscus. Last winter I wasn’t successful in this endeavor because I didn’t keep it hydrated well in the garage (my guess). However, I also overwintered some geraniums (yes geraniums) in the garage and we have been enjoying their flowers this year all season long. So, it’s possible. 

The best way to overwinter your tropicals or selected annuals, would be in a greenhouse or some location with plenty of light. Since a lot of us don’t have a place like that, most of us will be trying to help them limp through the winter in the garage. 

Before you bring the plant indoors, it’s a good idea to treat them with a little insecticidal soap or neem oil. You don’t really want to bring any insects indoors with your plants and not doubt, you will have some insects that have gone dormant already in the soil. So, a little insecticidal soap or neem oil should do the trick. 

Supplemental lighting would be a good idea also. LED grow lights are fairly expensive, so hanging a grow light above your overwintering plants is a way to help stack the deck in their favor if you will. 

Last but not least, be sure to keep the plants watered. They may lose their leaves and look a little ragged during the winter, but water will help them stay hydrated as they do their best to mark time during the winter. 

Also, if we hit a warm streak during the winter, there’s nothing wrong with setting them outside for an afternoon or a few days. It’s hard to beat that natural warmth and sunlight they are used to. 

Overwintering plants is always a gamble, but as gardeners we are gamblers, so give it a shot. You just might be able to keep that plant alive for next year. See you in the garden!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photos: Tom Ingram