The weather is due to change this weekend, becoming more ‘seasonally appropriate’. The past few weeks have been sunny and mild – nature has extended the growing season this year. But what about when she’s not feeling so benign?
Time to look at greenhouses again.
Where to put a greenhouse? The site should meet these criteria:
- Open position. Greenhouses need light so the site needs to be away from shade thrown by trees and buildings
- Level to ensure the structure is robust and water drainage flows
- Sheltered from the wind especially the North winds – the blowing of which can really cause the temperature inside to drop and rattle the structure itself
- Orientation – north to south will provide the most even light levels throughout the summer but in the winter, an east to west orientation will make the most of the available light
A few smaller considerations:
- Door frames take up light and throw shade on to the plants so thin frames are better in this respect
- To minimise the stress on the greenhouse structure a sliding door which hangs, is better than a conventional hinge mounted door
To heat or not to heat ?
Unheated greenhouses are referred to as Cold and are not frost free.
For a heated greenhouses the minimum heat level required would be to keep it frost free which means providing heat to ensure the night temperature does not drop below 2C and is kept between 5C and 10 C during the day.
For the garden greenhouse heating is usually provided in one of three ways:
- electricity or portable gas or paraffin heaters
If the source of heat is electricity it can be controlled by timers and thermostats. As well as greenhouse fan heaters, electricity can be used to provide power for soil warming cables which can be run through sand benches, heating trays and pots from underneath.
In summer when the temperature needs to be controlled downwards (tomato plants for example like warmth but not over 30C) the outside of the glass can be painted with Coolglass, a specialised white paint designed to reflect the light.
Also used as seasonal blinds are cloth and netting. These are also more effective fixed on the outside of the greenhouse to prevent heat actually entering the greenhouse.
In days gone by, heat was provided by stacking manure either under the benches inside the greenhouse or building a low manure wall around its exterior.
Which made me reflect that there are some lengths, to which I would not go for a homegrown tomato.
