Part 27 of a series by Eugene Howell
We’ve begun to have cold weather this winter in Florida. The temperature for three successive nights got low enough to do serious damage to any tropical bonsai which may have been left outdoors and unprotected.
The techniques typically used by bonsai owners to protect their trees when the forecast shows low temperatures coming are to either put the trees in a greenhouse (if your lucky enough to have one), bring them into the house or garage, or to place frost cloth over the trees and add heat generating light bulbs under the cloths to keep the air around the trees a little warmer. But there is one more method that most people don’t even know about — using microclimates.
Believe it or not, almost every homeowner has microclimates around his or her house and if you place your bonsai in one, you can go a long way towards keeping the damaging cold temperatures from harming your bonsai while at the same time avoiding a higher electricity bill caused by running those lights 24 hours a day.
Let’s define and discuss what a microclimate is and I’m sure each reader will begin to recognize where they may be on his property.
A microclimate is simply an area that, for one of many reasons will either remain warmer in winter (or cooler in summer), than the prevailing temperature in the general area. This temperature variance can be anywhere from 1 or 2 degrees all the way to a 10 degree difference. They are often created by manmade structures, the natural terrain or a unique combination of trees and shrubs.
For example, take a look at the exterior of your home as well as the fences around it. At each location where one exterior wall intersects with another you may have the possibility of a microclimate. If this spot faces East, South-East, South, or South-West, then you probably have one. The idea is that (in Florida) cold winds come from the West or North-West; therefore, the spot on the East side of the house has the opportunity to trap air that becomes warmer than the general area. It becomes warmer not only because the air in the spot is somewhat stationary, but more importantly, the sun will heat up these intersecting walls during the day and they act as radiators during the night. The same thing holds true for the ground below the intersecting walls. The result is a slightly warmer environment for the bonsai throughout the night.
A fence can also create a similar microclimate at the location where it meets a building or where two fences intersect, and where these intersections face East, South-East or South there is likely to be a microclimate.
microclimates can also be created with strategically planted trees and shrubs. When I was a kid I lived in Iowa for several years and saw many examples of this. Farmers would go out 50 to 75 yards from their house and barn on the North and West side and plant three rows of closely spaced fir trees. Then immediately inside this wall of trees they would plant another three rows of a fir which doesn’t grow as tall as the previous rows. Next, inside this, they would plant three to five rows of an evergreen shrub. After a few years they would have a living wall, from ground level up to about 40 feet that would almost completely stop cold winds from passing through. This would allow the farm yard to get several degrees warmer during the day than the area immediately outside this living wall. They had successfully created a microclimate that might be as large as two acres or more. The warmest part would be anywhere from 10 yards inside the living wall, out to about 40 yards from it and the temperature would gradually decrease as one went outward from there. If your landscape includes thick, fairly tall, hedges then on the South or East side of them, you may have a microclimate.
The natural slope of the terrain may also create a microclimate. Cold air will slide downhill. This means that if your property slopes downward, even as little as three or four feet, the cold air at ground level will slide downward into the lower part of the property. If this lower part is not a bowl (which will allow the cold air to fill it up and then spread out over the surrounding area) then the cold air will continue to move from your higher ground to your lower area and the temperature of the higher ground may stay a few degrees warmer. At my house, my backyard slopes downward for about six feet to the medium-sized pond behind the house. The resulting effect is that the higher part of my backyard stays sufficiently warmer that even with the temperature dropping to 30 degrees, most of my tropical bonsai don’t suffered any damage.
Never assume you have a microclimate without testing it first. You need to verify that it does stay warmer than the surrounding area. You can do this by placing a recording thermometer in the spot, at about 18 inches above ground level. The following day compare it to a recording thermometer that was placed in an area that experienced the full depth of the cold temperature at night. If you do this several times and one thermometer consistently reads higher that the other, you have successfully identified your own personal microclimate.
Photo credit: flickr Creative Commons, XV EXPOSICIÓ DE BONSAIS DE TARDOR CIUTAT DE VILANOVA by Premsa Ajuntament de VNG