With Winter not far away, I've put my outdoor heated
bed back together ready for the cold weather. Though not essential,
a heatbed has many benefits for enthusiasts in different climates.
Here
in the UK (zone 9) there is ordinarily little need to protect
my bonsai from the cold, however weak trees benefit from being
kept slightly warmed at the roots. As well as preventing the roots
of the tree being exposed to frost and freezing, the extra warmth
extends root activity further into Autumn and early Spring.
I
predominantly use my heated bed for recently collected yamadori
and other trees that have weak roots or are under stress for one
reason or another. In colder climates, heatbed's can be used to
protect trees that are more susceptible to frozen roots such as
Trident Maples and also mame-sized bonsai that are grown in small
pots.
A heatbed is intended for frost hardy trees only; whilst the soil
will be kept a little warmer than the ambient temperature outside,
the surrounding air temperature is not altered. Tropical's and
other frost tender species cannot be kept outside using this system
alone.
Here is some
of the soil warming cable laid underneath one of my benches in
my garage. The edges of this area are shuttered off with timber.
The soil warming
cable plugs into the mains and the cable itself heats up. It is
kept switched on 24 hours a day all winter; electricity costs
are minimal as the cable is low wattage. Soil warming cable can
be purchased at garden centre's and nurseries; it can also be
occasionally found second hand.
After the cable is laid on the ground, sand is spread over the
top of it. The heated cable warms the sand sufficiently to keep
any pots placed on top of it from freezing. I keep a thermometer
handy to make sure that the sand never climbs above 10°C;
warm enough to force many plants into premature Spring growth.
Adding additional sand reduces the temperature of the bed; removing
sand has the opposite effect, necessary if the sand isn't quite
warm enough in the coldest periods of the Winter.
Pictured below is the completed heatbed; I have placed a weakly
rooted Hawthorn air-layer that I had to separate a month ago.
This should keep it rooting for few weeks yet.
