Many of us “northerners” do not have the luxury of planting, willy-nilly just about anything in our gardens. For us, tropical gardens are a thing of the true tropics. Hawaii, the Caribbean islands, and Southeast Asia come to mind. Floridians and Southern Californians can get away with them to some extent, but for most of us in the northern hemisphere, we must treat tender perennials as either annuals or container plants that we overwinter indoors.
Making matters worse is the somewhat artificial distinction in the industry between indoor and outdoor plants. Most tropicals north or south of the tropics tend to be sold as houseplants in nurseries and retail department stores. These plants are not designed to be moved outdoors and are specifically bred and trained to survive in the somewhat unnatural confines of a human home. This of course does not mean that you cannot move them outside during the summer, many people do. However, there are a couple of gotchas to be aware of that are not usually shared up front by most plant care guides:
As you can see in the above photo, the sun-loving Jade Plant’s leaves are severely burned only after a single day in full sun. This plant has clearly not seen sun like this before and was bred to survive in an indoor environment. Fortunately, gardeners can train houseplants for the outdoors and slowly expose them to sunny conditions. For example, placing them outside for one hour each day in the first week and slowly extending the time as the summer progresses. The sun’s intensity in your climate can of course also affect the length and duration of this process.
Houseplant guides are notorious for claiming that tender tropicals are not to be exposed to temperatures lower than 50 or 60 degrees Fahrenheit (10-15 degrees C). However, if you were to look up the USDA hardiness zones of most of these houseplants, you’ll quickly find that they are far more hardy than these guides would have you believe. Again, this does not mean that you should suddenly move a houseplant with complete disregard for outside conditions. Instead, a smooth transition is preferred.
The other thing to consider is that most houseplants, unless we are transplanting them in the ground for the summer, will likely stay in pots or containers. As such, if overnight temps dip close to the lower end of a plant’s hardiness zone, then cold damage can occur far sooner for potted plants than for their in-ground counterparts. Roots in containers are much more exposed and susceptible to cold air than in the ground. This is often known as plants getting “cold feet.” Microclimates and a close proximity to a heated pool or doorway can help, but it’s good to be aware of these seemingly minor technicalities.
As overnight temperatures approach the freezing, most tropicals need to come back inside. It is also extremely important that we do not bring the outside in. Bugs, spiders, slugs, worms or anything else that may have set up shop in our pots all need to be dealt with. Here’s a great article with many useful tips.
As for overwintering plants that are generally not considered to be houseplants, but nonetheless need to be overwintered, a different approach may be needed. Oleanders (Nerium), for example, prefer cool winter temperatures, as do many succulents. In these cases, an unheated garage with a window or a cool, well-lit hallway would work far better than a warm living room.
Newly purchased houseplants at the end of the day are just normal plants that have never been outside. With a little extra knowledge and care one can easily grow them outdoors during the growing season. Some consideration should be taken while moving them in or out, but otherwise you’re doing them a favor by relocating them to a more natural habitat. Care guides and hardiness zones can be confusing, but with a little research one will find that most tender plants can (and should) be grown outside for most of the year in all but the harshest climates.