Page 20 - Simply Veg Issue 1 2016

Getting started in the Greenhouse
Kelvin Mason – this is the rst in a series of articles on growing crops in protected structures, which includes greenhouses (often called glasshouses commercially) poly-tunnels, cold frames and cloches
I will start off in this article considering the purchase of the structure and siting. Then in future articles move onto heating and equipment available for greenhouses and the following articles will cover the growing of crops under cover and how to use the protected structure to make full use of it.
Which direction your greenhouse runs will often depend on the shape of the site but for the best winter light it is better to run it East / West so it receives the most southern light. Although care needs to be taken that the crop on the south side of the structure does not shade that on the north side.
So the site needs to be open but also sheltered from the worst of the wind. Wind causes two problems for greenhouse growing, one is damage to the structure during high winds (I speak from experience as mine was blown down in the gales of the nineteen nineties!) The other problem particularly if you intend to heat the structure is that even light winds remove the heat and increase the heating costs considerably; the heat loss is double if the wind speed increases from 0 mph to 15mph. In fact the rate of heat loss is affected more by the
Before you buy a greenhouse or poly-tunnel you need to decide where it is going to be sited as this will often dictate what size you can buy. Whatever size you think you need, buy the biggest you can afford and t into the site as once you have a greenhouse or poly-tunnel
you will soon ll it and want a bigger one! Greenhouses (and I include poly-tunnels when I refer to greenhouses in this article) enable you to garden all the year round and with the right choice of crops you can be picking fresh vegetables all the year round. They have other uses as well including:
Starting early crops - so that you can
pick them when they are expensive in the
supermarkets or greengrocers.
Propagating plants – including vegetables and
owers by both seed and cuttings.
Growing tender crops – such as melons,
indoor tomatoes, cucumbers and peppers
Overwintering tender plants – mainly
perennial owers
Growing winter salad crops
Providing protection for late owering plants – like Chrysanthemums.
Siting the structure
The site should be in full sun or only partial shade if you are to get the best out of the structure. A sunny site means the plants get plenty
of light for photosynthesis so make the maximum growth. Light is
the most important factor in growing good crops and greenhouses must be designed and sited to get the maximum light transmission. Having said that one of my greenhouses is in nearly 50% shade,
from a neighbour’s Christmas tree and still produces reasonable crops; so some shade is not the end of the world. At least it saves me shading the greenhouse in the summer so it does not get too hot! Light whether direct sunlight or diffuse light is even more important in the winter when the day lengths are shorter and the light levels lower especially on dull days. To give exhibition crops a good early start some form of supplementary lighting may be required which I will cover in a later article.
wind speed than the outside temperature. If your site is prone to high or regular winds either plant or put up some form of windbreak. This needs to be far enough away to avoid shading the structure but close enough to reduce the wind speed by 50%. Windbreaks should not be solid structures like walls
or fences, but perforated like a hedge or windbreak material. The aim is not to stop the wind but to lter it and reduce its speed.
If the wind break is solid this causes turbulence which is even worse. The prevailing wind in the U.K is from the southwest but this may not be the case where you live owing to local topography; so check this out. The coldest winds tend to come from the north and east but fortunately are not that common.
Greenhouses need a level site otherwise construction is very dif cult. If necessary level the site by “cut and ll”, that is cutting out some of the soil from the high side and use it to make up the low side to the required level. Poly-tunnels can be built on sloping sites but you need to be aware that the cold air will ow and collect at the lower end of the tunnel making this end colder.
It is wise to consult your local planning department to check if planning permission is required. This seems to vary around the country but it is best to check rst and apply if you need permission. If you are going to put the structure on your allotment check that this is allowed as not all sites will.
Although hopefully you will collect the water from the roof for watering it is likely you will need additional water during the summer, so consider laying a water pipe to the greenhouse to save you having to carry cans of water or running out a hosepipe each day. If you install a permanent water pipe you will need to consult your water company and ensure it is the correct type of pipe and the right depth. If you are going to connect the pipe to some form of diluter for feeding plants you should have a break tank and non-return valve tted to stop the water back syphoning into the water mains or your drinking water.
Once you have had your greenhouse for a couple of years you will want to work in it during the winter or early spring evenings when it is dark or you may want to install supplementary lighting. To do this will require a protected cable laying to the greenhouse. This needs to be connected to your electric supply by a skilled and quali ed electrician.
Choosing your Greenhouse
The rst decision is what size and as mentioned above go for the largest you can afford and t onto your garden or allotment. The length and width of the greenhouse and poly-tunnels vary greatly so it is likely there will be one to suit your site.
with the right choice of crops you can be picking fresh vegetables all the year round
20 simplyvegetables
Dutch light type greenhouse