People in glass houses

14/01/2008

The BBC has a maxim – “educate, inform and entertain”. I know this because MT’s editor told me that’s what I should strive for in my monthly articles. Well, so much for the first and last parts of the motto, but I think I’ve hit the nail on the head this month with the middle requirement – if you were planning a greenhouse for your garden that is.

Most keen gardeners would not be without some sort of greenhouse. They extend the gardening year and provide a frost-free environment for over-wintering tender shrubs and plants.

The word “greenhouse” covers a multitude of purposes: from cheap mini greenhouses - basically small shelving units covered with clear plastic retailing for about a tenner - to huge commercial buildings costing tens of thousands of pounds.

If you already have a greenhouse you will no doubt by now have fumigated and cleaned it ready for the coming months when it will become full to the brim with seedlings. If you don’t, and were thinking of installing one, now is a great time to give serious thought to greenhouse gardening. The positioning of a greenhouse is very important: take care to observe the shadows cast by neighbouring buildings and trees during winter and spring - you won’t want your greenhouse sited in full shade.

If you plan to use the greenhouse to raise seedlings and to over winter tender specimens - mostly in the spring - position its longer axis in an east-west orientation, giving good light for much of the day. Greenhouses intended for summer use are best positioned north-south on their longer axis.
Free-standing greenhouses need sheltered, open sites. For lean-to greenhouses a wall that has equal sun and shade is preferable but be careful not to site it where the sun shines for most of the day: it will become too hot, even with shading paint or blinds.

The choice of greenhouse will be governed by space and budget but there are differently shaped houses designed for special uses. The traditional span design is practical both for growing space and head- room. Dutch light greenhouses have sloping sides designed to make the most of maximum light and are a far more unusual sight in a private garden.

Alpine houses are traditional timber framed buildings with louvered vents all along the sides for efficient ventilation. They are used for hardy plants that love light and well-ventilated conditions but need protection from wet conditions.

Greenhouses intended for summer use are best positioned north-south on their longer axis.

Conservation greenhouses, very popular with the Green movement, are designed with extra features that make it as energy efficient as possible. Roof panels allow for optimum light penetration, and mirrored surfaces reflect light within the greenhouse. Double-glazing and specially made insulation are standard fittings.

Plastic greenhouses, or Polytunnels, are basically a tough plastic sheet fitted over a hooped framework. They aren’t pretty and are generally used more by commercial growers or very serious vegetable gardeners. But they are relatively cheap and can be easily moved around the plot - quite important if you follow a crop rotation system of growing.

As you would imagine, greenhouses are available in a range of materials including plastic, aluminium, and both hard and soft woods. The hardwoods are more expensive and cedar is possibly the most usual of the hardwoods to be found. If you buy a softwood greenhouse you will need to apply wood preservative before assembling.

So there we are. Not a hugely entertaining article (I did warn you) but hopefully you will feel a little more informed and perhaps a tiny bit inspired to think about getting a greenhouse this year.