The greenhouse during the cold season
I maintain my greenhouse out of frost. I use for this purpose a electric blowing heater of a power of 3.3 kw.
I made a few changes to it :
- The original thermostat being not accurate enough, it was necessary to install another one. This is external to the heater, which allows me to place it wherever I want in the greenhouse, regardless of the heater;
- The thermostat acts only on the heater. This means that the fan is constantly on. Which was not previously the case.
Considering the energy price, I isolate my greenhouse using bubble wrap specially designed for this purpose (coarse bubble plastic, UV resistant - not to be confused with the plastic with small bubbles for packing fragile items).
Originally, I had placed the insulation inside the greenhouse. Unfortunately, once the cacti are installed on the shelves, it becomes very difficult to remove the insulation. It has remained in place for several years, until I found a German supplier selling a fixing system suitable for outdoor use.
These clips consists of two parts:
- One is glued to the glass (using silicone glue - this is done once and for all). The bubble wrap is pinned on that part;
- The other part is screwed onto the first one, fixing the bubble wrap.
As can be seen in the photo (right), I have to use two strips of plastic to cover the entire height of the greenhouse. It is 1.70 m while my plastic is only 1.50 m. Which means that I have a double thickness of insulation on most of the height. I use these two strips to cover three sides of the greenhouse. This work is done in just one hour (same for disassembly).
On the fourth side, there is a sliding door. I must work differently on this side. The surfaces located on each side of the door are isolated from the inside, the door is isolated from the outside. The tip of each gable is isolated from the inside. The bubble plastic used inside remains in place throughout the year.
Inside the greenhouse, in view to reduce the volume to be heated, I stretched a clothesline up the gutters on which I put a double layer of bubble wrap.
During my visits to other collectors, I have seen other forms of accommodation for cacti. But none of those can be used as winter shelter. The plants are then returned to the main greenhouse that is equipped with a heating system and brought outside when spring is back.
On the website of Willi Gertel, we can see a much more sophisticated installation. Besides the aluminum table (like those used in garden shops), everything is homemade. Here are the "trade secrets" revealed by Willi himself.
The base of the frame is composed of a 10 cm layer of insulation on which rests a "sheet" of aluminum 1.5mm thick. Above this aluminium foil, there is an empty space of 16 mm wherein is installed an electric heating cable. Above this gap, is placed an aluminum sheet of 3 mm thickness on which are placed the plants. The frame itself is composed of Plexiglas Alltop® multi-skin sheets of 16 mm thickness and aluminium profiles. Plexiglas Alltop® has been chosen for its high UV transmittance (unlike polycarbonate).
You'll understand that with this system, it is no longer necessary to move plants.
Another big advantage with those kind of horticultural frame systems is that the plants are in the great outdoors!