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Greenhouse Heating
Greenhouse heating is a subject that is often governed by economics and the gardener’s needs, so to this end I thought I would show you my set up as opposed to generalising. I have one 3m x 2.4m (10’ x 8’) heated greenhouse and three various sized unheated greenhouses, plus a 2.4m x 0.9m (8’x3’) cold frame. The 3m x 2.4m greenhouse is used primarily as a propagating area and a place to store plants requiring frost protection during the winter The other three greenhouses and the cold frame are used as ‘hardening off’ areas in the spring and for growing subjects that require protection during the rest of the year. These greenhouses are generally kept empty over the winter months. If I were asked what item is of most benefit to the gardener, then I would have to say the cold frame. The cold frame is in use all the year round Every garden should have at least one, even if it is of the flat pack variety and is erected / dismantled as required to save space.
Insulation; In winter I insulate my heated greenhouse on the outside rather than the inside. I find this method of insulating keeps my greenhouse much dryer i.e. less condensation forms and gives me more space. It also easier to fix in place otherwise I would have to remove and refit the shelving.
Heating; For economic reasons I have three forms of heat set at various temperature levels rather than having a general temperature throughout the greenhouse, they are as follows;
General heating; When I require ‘frost free’ conditions, I operate with a thermostatically controlled fan heater set to give an ambient temperature of 35°-40°F (3°-5°C). When I start up my seed and cutting programme in January/February I raise the fan heater output to maintain a general air temperature circa 50°F (10°C).
Bottom heat; I have a thermostatically controlled heated bench for rooting cuttings or germinating seed that require a temperature of between 50°/60°F (10°/15°C). The 2.1m x 0.75m (7’x 2.6’) hot bed is a box formed with treated timber and lined with 1” (25mm) thick polystyrene sheets, and filled with river sand. In the sand, is placed an 25m (80’) 300watt soil warming cable controlled by a ‘Rodstat’
High level heating; When temperatures of 65°F (15°C) and above are required, I use a purpose made 575m x 290mm. thermostatically controlled propagator, which I manually adjust to the desired temperature.
Lighting; I use a time controlled fluorescent light above the hotbed to supplement the poor natural light of the winter months, thus speeding up growing/rooting times.
This is my current layout; The bottom shelves of my benches have been constructed at a height suited to getting bags of compost under.
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