PROTECTING YOUR TROPICALS OVER THE WINTER CAN BE TRICKY
Everyone loves showcasing bananas, palms, giant-leaf Colocasias and other tropicals in their summer gardens, but it’s no longer summer, so if you would like to enjoy them another year, you need to provide some wise winter protection.
Most of these tender semitropical plants are only hardy to Zones 7 through 10. Depending upon where you live, and the zone in which your plants are truly located is the differential you need to establish. Zoning is tricky and depends upon exposure to prevailing winds, elevation, land openness or the shelter created by surrounding forests and hills. Micro climates exist everywhere, so not all areas are the same, even if they are close by. Only experience over time will help you determine the true cold tolerance of your plants.
South Vancouver Island is Zone 8 on the outer areas, but perhaps becomes Zone 7 as you move inland. Higher Island areas may be Zone 6. Our Gulf Islands vary from Zone 7 and 8 to some areas reaching Zone 9 conditions. Coastal areas have the same variance and inland locations may go from Zone 7 to 6 but at higher wind exposed areas, possibly even down to Zone 5B. Basically, when you are looking at winter protection for your tender plants, everything depends upon the proven climatic zone in which you live.
When looking at so-called “hardy” bananas, especially the most well-known Musa basjoo from the northern islands of Japan, we find they really are a Zone 7 plant. This means that in Zone 6, like most of the Fraser Valley, they need winter protection when the temperature drops below -8 C to -10 C. Once these bananas are well established, the good news is they will produce underground shoots, and even if the top is frozen out, they will grow back out of the ground.
When the weather warms up, they can reach sizes of three to four metres high. This is especially true if you mulch the root system with 15 to 20 centimetres of bark mulch or sawdust. However, if you want to save the main stalks, just before the cold weather arrives, cut off all the leaves. Drive a tripod of stakes into the ground about a foot away from the stems, making sure the stakes are tall enough to more than cover the full height of the remaining stems. Secure the three stakes together at the top to form a peak. Using poultry wire placed outside this framework, create a cage all around the plant and fill with leaves or mulch to the top of the cage.
Next, wrap the outside with plastic to prevent winds from dispersing the leaves, to keep the material dry, and to increase the insulation factor.
The advantage here is that you will have a much larger plant, much earlier in the summer.
By the way, red bananas are not really bananas at all, but rather the Ensete ventricosum ‘Maurelii,’ a Zone 9 tropical which must be inside before any significant frost hits.
Citrus also need protection because they are Zone 8 plants with leaves quite susceptible to frost. In Zone 7 and above, they can be left outside in the most protected locations. Before cold weather arrives, their pots must be nestled into the ground, and framed in with a tripod of stakes. I’m a huge fan of the white insulating material called N-sulate and the “Ultimate” grade has a frost tolerance of 10 C. It is more effective when it’s dry, so when heavy frost warnings are out, wrap clear polyethylene around the frame to minimize any freezing. Double or triple wrapping with N-sulate will make a big difference, too. I’m quite disappointed that more folks don’t try to grow bay trees outside. In most of Europe, it’s standard garden fare, and in addition, they can be shaped into stunning topiaries. Bay laurels, Laurus nobilis, are Zone 7 to 8 plants and they not only provide a unique form in the garden, they are a wonderful continuous source of bay leaves for your favourite recipes. At our former home, we had one four metres high and three metres wide that tolerated our worst Valley winters. While it was a young plant getting established, all I did was create a tripod of stakes to over the top, and wrap it with N-sulate during the coldest parts of the winter. By doing so it became a little more weather resistant each year, and last year, at -22 C with the wind chill, it was not even wrapped and it still survived!
Palms are a little trickier to overwinter, especially the very popular Trachycarpus fortunei or Windmill palm, which is classed as Zone 6 to 7. It is one of the hardiest palms and in Zones 7 and 8, if well established and out of winter wind tunnels, it will survive just fine. These are icons on English Bay in Vancouver, and there are many specimens throughout Vancouver Island, the Gulf Islands, and in certain spots in the Fraser Valley.
The challenge in Zone 6 and colder is wrapping palms properly. Again, perhaps the easiest way is to create a broad tripod to reach up over the topmost foliage. Your framework will have to be strong and stable enough to support both the insulating material and polyethylene you’ll need to prevent any water from getting into the crown and freezing. This is especially true with a snow load on the poly tent. I would make sure the stem is also protected and would then even mulch the roots for extra insulation. A friend of ours kept an amazing palm outdoors for years, and he used a heating coil around the root zone in the worst weather. If your palms are potted you have two choices: Either sink the pot into the ground in a protected location or, if you have the room, put it into an insulated outdoor room during the worst cold. They can even be laid on their sides if they are too tall.
Giant leafed Colocasias and Alocasias cannot stay outside. If they have become too large and spread out, you have the option of cutting the leaves off so you only need to deal with the stems. It will take a bit longer to regenerate the leaves in spring, but by keeping it beside a warm window or in a greenhouse, it should start new growth in two to three months.
Standard, or “tree” forms of fuchsias, lantanas, heliotropes and other similar tender perennials should be trimmed back, defoliated, and kept from frost in an insulated garage or shed, or even a frost-free crawl space under a home. If all you have is a small patio in an apartment, place them in a tall thin box, insulate it both inside and out, and place on a sheltered deck. They should stay dormant until late winter when you can take them out, and, still providing necessary protection, allow them to begin leafing out.
The above may sound like a bit of a chore, but trust me, these specimens are all well worth the effort.