A Guide to Hot Houses

Did you know that there’s actually a difference between greenhouses and hothouses? The idea behind both is similar.

They provide an enclosed garden space and allows you to grow plants that would not survive on their own outside in the local climate.

These buildings are also useful for “forcing,” which is defined as causing plants to grow before their natural season.

A Hothouse for Home & Garden

The distinctive difference that defines a hot house is the temperature. Greenhouses are often either cold garden greenhouses that are seldom used during winter, or frost protect greenhouses that aim to keep a minimum temperature of 7 degrees C.

However, a hot house is designed to keep a constant temperature above 16 degrees C (70 degrees F). This higher, more stable temperature allows for the cultivation of tropical plants such as melons, peaches or even orchids.

Even with today’s energy efficient building materials, maintaining a hot house using conventional heating methods could be remarkably expensive.

Typically, frost protect greenhouses are heated using paraffin, gas or electricity. However, even if one could equip a greenhouse with enough of these conventionally-fuelled heaters to maintain 16C or higher, the energy costs would be prohibitive, not to mention decidedly environmentally unfriendly.

Heating a Hot House

One hothouse heating solution involves burying hot water pipes beneath the soil. Water (or other fluid) is heated by conventional methods or by solar panels. As the water circulates through the pipes, heat is transferred to the soil and eventually throughout the greenhouse.

Another take on this is to bury heating cables in the soil. As electricity runs through the cables they heat up and this heat is transferred to the soil. Although these arrangements are more efficient that installed heaters, they still require large expenditures of energy.

However, there is a more energy efficient and eco-friendly way to do things. It involves reviving a Victorian practice that is still very feasible and effective today.

It’s called the manure pit. As manure composts (or rots), it produces heat. Perhaps there was one day in the past when someone noticed that seeds on the manure pile grew more quickly than seeds planted normally. However it happened, the concept of hot bed gardening was born.

To give this a try, mix manure with organic matter such as straw or dried leaves. You should have about two-thirds manure to one-third organic material. Manure from farm animals is preferred (horse, cow, rabbit, sheep, fowl)- domestic animal manure can contain parasites. Cover this mixture with a layer of soil. As it decomposes, the soil above will be heated.

You should be aware that decomposing manure can give off gases that may be irritating or even dangerous in high concentrations. Make sure your hothouse is properly ventilated. Other concerns that troubled the Victorians when they used this heating method include random hot spots and overall temperature control.

As is the case with most garden buildings, your hot house should not require any planning permission as long as it stays below general height requirements – no higher than 4 metres with a pitched roof – and doesn’t encroach on the space between your house and public highways.

There shouldn’t be any specific concern about the method you use to maintain your hothouse temperature. But it never hurts to contact your planning authority and confirm that your plans are okay.