Growing bamboo and other exotic plants in climates far removed from their native ones typically requires some "man-made" accommodation. For those of us in zones 5, 6, and 7, this essentially means winter protection. This absolutely brutal winter has inspired me to consider the most effective winter protection methods, even those that seem extreme.
First, an admission. I was lazy this year and, relying on the string of mild winters we have had here in Southern Ontario, I thought I could get by with mediocre winter protection. In the spring, I think I will have found that I learned a costly lesson. So, never again. From now on, winter protection will be a top priority!
Below are a number of different means of winter protection, some cheap, simple and easy to implement - others not so much.
1. Use planters that you can move into protected environments during the coldest months
This is of course the simplest winter protection method and something I have done myself with a number of my plants. You need not be relegated to small pots. Planters as big as 20, 30, and 40+ gallons can be moved with some equipment (e.g. a dolly, or wheels attached to the base of the planter). This allows you to grow relatively climate-sensitive specimens that can actually achieve quite a large size. I have seen 14'+ bamboo in large custom planters. Of course, finding a winter home for such plants and planters may prove a bit of a challenge. A well-insulated greenhouse with some added propane/gas heating would be the "gold standard" for over-wintering such plants.
2. Mulch
Mulch is the mainstay of any winter protection program for plants that remain in the ground. Mulch basically helps the soil, and hence the roots and rhizomes of a plant, retain heat and moderate temperature drops. It does this by better absorbing solar radiation than bare soil (or snow for that matter) and by insulating the soil. For example, although the day's high may only be -8C, to many bamboo that compares very favourably with a low of say -18C. Mulch will help the soil spend more time at -8C (or higher because of its absorption of solar radiation) and less or no time at -18C.
People tend to be very loyal to the mulch they use, and there is no single perfect mulch out there; however, when considering ONLY winter protection, Straw has the best insulation capacity. This is also why rodents like to nest in it. Straw also tends to rot easily. I have read that applying straw in early winter, after a solid frost (mid/late November for most of us in Southern Ontario), helps prevent rot and rodent infestation. While one could leave the straw in their planting beds in the spring, I would rather remove it and dispose of it.
Another admission. I have yet to use straw. I typically mulch with 6-8"+ of a pine mulch and shredded leaf combination. The insulation is relatively good and I don't have to pick it up in the Spring. I would use straw on zone 8 bamboos, on bananas, and on palms (but I don't have any of those yet!).
3. Tarps, Blankets, Coverings of Some Kind
Depending on the hardiness of the varieties grown, covering bamboo with some sort of tarp, blanket or thick poly sheet may be necessary.
This year, I used a cheap clear plastic sheet on my P. Spectabilis and I am sure I will pay the price for it. For most plants, I would use a 3 to 5 mil poly sheet, or as it is know in agricultural circles, "overwintering film".
If you are growing a marginal bamboo for your climate, I would instead invest in a high-quality frost blanket. Why go to all the effort of growing an exotic plant and not invest in protecting it? DeWitt is a popular manufacturer of frost blankets which come in weights of up to 3.0 oz.. The 3.0 oz "Ultimate" blanket claims "up to 10 degrees (F) of frost protection" compared to the ambient temperature. Expensive? Sure. Extreme? Somewhat. Worth it for a plant that you have spent two or three years nursing and that would be difficult to replace? Absolutely.
This year, I also used a tent-like woven poly frost blanket for my F. Scabrida. These are great as they are easy to set up and use, but the largest of these particular tents that I have seen seems to be about 4 feet high. I suppose one could perhaps bend over a 7 or 8 foot tall bamboo and cram it in there, but obviously, plants taller than about 8 feet and wider than about 3 feet will not fit in these tents.
Custom build structures using chicken wire and filled with some insulating material are also typically very effective. See this post on Steve Lau's blog for an example.
On a final note, I have read that light transmission is probably not important for
bamboos during the winter as they remain dormant and do not
photosynthesize sunlight. This is why bamboo covered in snow for three
months typically looks ok in the spring.
4. Chemical Treatments
Now we are really entering the realm of extreme winter protection. There are two chemical treatments that one could use to help overwinter bamboo and other plants. These are both "anti-dessicants' but one is meant for leaves and the other for roots. These essentially help a plant hold onto its moisture and prevent dessication by coating the leaves and roots with a waxy yet bio-degradable film. Wilt Pruf is the most popular anti-dessicant for leaves. Root Zone is an anti-dessicant (or anti-transpirant if you prefer) for the roots of a plant.
5. Radiant Heating (experimental)
So you've mulched, tarped, used anti-dessicants, and you are still worried. Well then you probably shouldn't be growing what you are trying to grow in the climate zone you're trying to grow it!! But let's assume you love the challenge and damn it, you want the yard of your cottage in the Muskokas (zone 5a/b) to look like Tahiti. Ok, there is one last extreme winter protection method I can suggest - though it is experimental and I have never tried it.
Basically, the idea involves the use of outdoor spotlights or "brooder lights" fitted with infrared heat lamps. Typically, these light fixtures can support anywhere from 150W to 300W bulbs. 175W and 250W infrared bulbs are fairly widely available. During extremely cold periods, one could conceivably aim one or more lights at a plant. Because the heat is of the radiant type, the plants would be heated so long as they were exposed to the light.
There are a number of issues with this idea. Some of these are:
1. Cost and Complexity - obviously difficult and expensive to set up and operate
2. Heat Damage - if the lamps are placed too close to the plant, if they blow onto the plant, or if they are simply too powerful, heat damage is a risk. Fire is also a risk.
3. Complaints - Neighbours may not take too well to a bank of red lights glowing in your yard throughout the night, though if you want to get really extreme, you could avoid this by getting ceramic dull emitter infrared bulbs, which emit no visible light, only infrared light.
If you have tried all of the above and your plant still dies from cold-related injury, then you may be trying to grow an tropical Orchid outdoors in Winnipeg. I can't help you!
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