Overwintering Outdoor Tropicals
Summer is drawing to an end and night temperatures will soon start dropping. Before your tender and tropical plants get chilled, learn how and when to protect them with these tips.
Zones 9 & 10
Those plants rated zones 9 and 10, like red bananas (Ensete ‘Maurelii’) and colourful foliage tropicals, such as philodendrons, dracaenas, tender palms, and tropical hibiscus, really need to be moved to a warmer indoor location soon, usually by mid-September. The goal is to transition them inside while the light quality and humidity level are still quite good, and before our home heating system is fired up, and certainly before the night time temps hit 10C.
Acclimatize them for about three days before fully moving them indoors. i.e. place them inside at night, out in the day, or bring them into the garage for a few days)
Place these plants in the coolest location in your home, preferably next to an East or North window, far from heat vents and further still from a fireplace. If the optimum placement is not feasible, a South or West window is better than no light at all, and grow lights or fluorescents can also be a great help.
Once inside, mist the foliage a couple times a day to add some humidity, but make sure the leaves are dry at night to minimize any disease issues. Keep them rootbound in their same containers, and don’t feed them until April, when growing conditions improve.
Zone 8 tropical plants are best left outside until night temperatures drop to about 4-5℃. This also applies to fuchsias, lantanas, angel trumpets, colocasias, and canna lilies. Although they are a little more resilient, they also cannot tolerate a frost and must be given protection. The longer you can leave them outside, however, the lesser time they will spend in a dormant or semi-dormant state.
Putting them in a winter dormancy situation means stripping all foliage off, leaving only bare stems and branches. Canna foliage can be cut low, but the leaves of colocasias must stay on. They need to be kept at a temperature ranging between 5-10℃ and have some access to light. The soil should be kept just slightly moist to prevent desiccation, but not so damp as to cause root rot.
Citrus is a challenging category. Citrus prefer to stay above 5°C, so when night temps approach this point acclimatize them indoors. The issue most folks have, however, is that while they love being outside all summer, when they are brought inside the leaves begin to turn yellow and fall off almost immediately. The reason for this is because when they are indoors, they love it cool, humid and very bright, and our houses in winter are anything but.
To help prevent this, keep them in the coolest room in your home, next to the brightest window for best performance. A conservatory or greenhouse that does not freeze is ideal, or even a cool garage with a window for light can work. Mist the foliage as often as you can, and keep the soil just barely moist.
If left outside, they will tolerate a light frost, but not temperatures lower than -2 to -3℃. In warmer regions, such as areas rated zone 7 and 8, they may get through nicely when protected by a product like N-Sulate, but you will need to keep an eye on them.
By far, the most popular outdoor tropicals today are vines, like mandevillas or dipladenias. They are incredible performers in the hot sun and come in colours of red, hot pink, white and soft pink and they out-flower virtually anything else on the patio! They require warm temperatures, in the range of 15 – 20℃, to overwinter, so be sure to bring them indoors when outdoor temperatures start dipping into this range.
When you bring them in, cut vines back fairly hard (down to 25 – 30 cm), place them near a bright window and keep them on the dry side. This will help them to overwinter well. Be sure to check the leaves thoroughly for scale, as it is one of their main pests.
Eucalyptus and Green Banana
Eucalyptus is another plant that has become very popular outdoors but, unfortunately, does not fare well indoors. One of the hardier varieties, Eucalyptus gunnii, is a zone 8 plant that, if the pot is sunk into the ground on the South or West side of your home and wrapped with N-Sulate, can potentially make it through a winter with temperatures of -8 to -10℃. To be on the safe side, however, consider placing it in a cool garage with a window to overwinter.
Musa basjoo (green banana), is native to the northern islands of Japan and in zone 6 it can be planted in the ground and, after a year or so of being established, can be cut down, frozen in the ground, and still survive to spring. The first year they need to be protected by cutting off the foliage in November and wrapping the trunk with both insulating material and plastic to prevent water from seeping into the stem.
Perhaps the most controversy takes place regarding how to overwinter hardy palms, such as the windmill palm (Trachycarpus fortunei). In a protected location, windmill palms are considered a zone 7 plant. Over time, as they become established, they will tolerate temperatures down to -10 to -12℃. In zone 6, they will need some proper winter protection to survive.
They need to be located on the South or West side of your home with the pots buried in the ground, both for stability and root protection. When the temperatures drop to -8 to -10℃, the top leaves need to be tied up loosely and covered with N-Sulate, then wrapped with plastic to prevent water from getting into the crown and rotting out the centre. It is also a great idea to wrap the the roots with heat tape and the stems with an insulating material, as well. This only needs to be done during a period of cold weather. Otherwise, enjoy their beauty all winter.
Inspecting Your Outdoor Tropicals
Before you bring the plants inside, do a very thorough inspection for any insects or disease problems. Outside, over the summer, they many have provided a nice home for many insects, especially in the soil. A wipe down with a damp cloth soaked in a mild soapy solution, like Ivory Snow, will catch potential insects and their eggs before they become a problem.
As for the soil, though, there aren’t many products available to control soil-borne insects. For crawling species, dust the soil with diatomaceous earth and for fungus gnats, apply about one-inch of washed sand on top of the soil as a deterrent for any adults wishing to lay eggs.
It’s been a perfect summer to have tropical plants gracing our patios, but now it’s time to ensure they do well over the winter so you can delight in them again next summer. While overwintering can be a learning experience, it can also be overwhelmingly gratifying to see, so put in the work now for an unbelievable season to come!
For additional information on caring for tender plants over fall and winter, click here.