If you want to grow food crops, like tomatoes and peppers for instance, a wooden greenhouse made from sustainable red cedar is the best option. It will provide far more ambient temperatures than a metal-framed aluminium greenhouse. I have both and my anodised aluminium, although it looks lovely, is noticeably colder in winter than my cedar greenhouse. It’s less useful for that reason.
Siting your greenhouse needs careful thought and the first consideration is heating. If you want a heated greenhouse, position it as close to your house as possible so that a cable can be routed easily. Electric frost-breaking heaters are the most efficient, but you can also raise plants using an electric propagator such as the Vitopod.
Siting your greenhouse is a complex issue. Choose a level site, but avoid frost pockets and areas under trees. Alignment varies according to use.
Positioning the greenhouse lengthways, in an east-to-west position with the door at the western end, will maximise light throughout the year. A north-to-south alignment provides light on both sides in summer and many who grow only summer crops prefer this. Decide what you want to grow, that’s the key thing.
The greenhouse nitty-gritty
It’s never easy to decide and in many cases your garden may restrict the choices. Level ground and good light are essential, as is a professionally laid base. Factor that into your costs and do look for offers which often crop up in autumn.
Summer crops - go north to south with door at south
The most popular reason for owning a greenhouse is to grow tomatoes and cucumbers etc. If this is the case, go for a north-to-south alignment, and choose a traditional wooden greenhouse with top vents and side panels that lift up to allow the air in. That way your crops will get some summer sun on each side, but not the full force of hot midday sun along the length. A soil floor, with a simple path, is the best option. A concrete or paved floor throws up too much heat.
Heating will not be necessary if you use it in summer only as long as you don’t put anything in the greenhouse until late May. If you wish to get your tomato plants in earlier, by early May for instance, be prepared to fleece at night. If you want them in even earlier in the year, put in electricity and buy a frost-breaking electric heater with a sensitive thermostat, one that’s the right size for your greenhouse.
Overwintering borderline plants
If you wish to overwinter borderline plants, such as agapanthus in pots, these will survive in an unheated wooden greenhouse sited north-south, without any heating. Dry your plants off from mid-September by easing off watering and feeding. Use rugged pots. British terracotta is the best material and Whichford pots are ideal, although expensive. Bear in mind they will outlive you. www.whichfordpottery.com Be prepared to fleece in cold weather.
Overwintering tender plants - go east to west - door at west - with electricity
If you wish to overwinter tender plants, like pelargoniums and fuchsias, you should use an east-west alignment so that you get good winter light. You will need heating and electricity is the easiest option, because heaters can left on and thermostatically controlled. A wooden greenhouse is more efficient to heat: it’s estimated to cost 20% less to heat than a metal-framed one.
The position of your greenhouse in an east-west position will create hot conditions in summer. So if you plan to use your greenhouse for tomatoes and cucumbers etc, you will need to shade. Greenhouse shading can be bought by the metre, with ready-made holes so that it can be attached to hooks. www.twowests.co.uk Two Wests also do a very wide range of greenhouses of all types.
Summer use only - go north to south - door at south
If you are only using your greenhouse in summer, aluminium is an option for you. Basic greenhouses, although not beautiful, are functional and less costly.
Style and substance
If you want to be more fashionable, Hartley Botanic do a full range from the modest patio affair to bespoke. Their Botanic Glasshouse range has part-brick sides and these sides hold warmth. There is also a modern, rather angular glasshouse, The Horizon, full of contemporary style. Planning position is not needed in most cases if the greenhouse is less than 15sqm.
Bear in mind that the steeper the pitch the better the light and the better the growing conditions. If money is no problem, there are lots of options to suit a variety of pockets. You do need to telephone and ask for prices and Hartley will also install. www.hartleybotanic.co.uk
Roof vents are vital in my opinion. Automatic vents are definitely an essential if you plant to use your greenhouse a great deal.
Try to have a hose nearby and get into the habit of morning watering if at all possible. Plants grow best with a morning regime, especially tomatoes. Water butt water, collected from the greenhouse guttering, is alright for fully grown plants. However young plants and seedlings need mains water, ideally left to warm up and lose chlorine in a watering can. Always fix up water butts and www.greenhousesensation.co.uk have some space-saving ones that look good.
If you grow and raise your own plants, staging is vital. If you overwinter plants you will also need staging. If you use your greenhouse for tomatoes etc, it is not needed and can even get in the way. Most greenhouse packages have one side of staging included.
Heating greenhouses is expensive and uses fossil fuel. Having a couple of full water butts inside in winter will hold heat and will save fuel costs. the water can be used for watering, but this system will depend on space.
When the tomatoes come out in October, add some winter salad crops. Seeds can either be sown in mid-September, or plants can be bought in early October. There are spicy mixes containing mustard, rocket and mizuna, and gentler ones using spinach and winter lettuce. Try www.organicplants.co.uk for ready-grown plants.
Alton - www.altongreenhouses.co.uk
Gabriel Ash - www.gabrielash.com
Electrical Heaters and Propagators