Gardens: 'Most polytunnel crops like plenty of sun'

Growing your own fruit and veg has never been more popular. But if you dream of melons in summer and baby leaf salads in winter, you're going to have to invest in some form of shelter.

Gardener and author Joyce Russell took the leap into the world of polytunnels 16 years ago and hasn't looked back since. "I live in Ireland where we get a lot of rain," she says.

"Most of the major outdoor crops, like potatoes, brassicas and carrots, do very well, but it is hard to grow tender ones like tomatoes, aubergines, peppers and cucumbers without some protection. The polytunnel keeps temperatures higher than the great outdoors."

A polytunnel seemed like a major investment but it paid for itself with the food grown inside within a couple of years.

Having quickly become an enthusiast, Russell began writing articles about the subject and she's now had a book published, The Polytunnel Book: Fruit and Vegetables All Year Round (16.99, Frances Lincoln Ltd).

The book lists plenty of convincing reasons to invest in a polytunnel - it costs a fraction of the price of a traditional greenhouse; it's put up quickly to cover a large space; it provides a warmer environment than outside; it blocks wind, and shelters from rain. As well as general good gardening advice, there's a month by month guide to jobs and a list of key crops.

So what would the polytunnel owner be doing in February? Tasks might include washing the polythene and frame and scrubbing down fixtures and fittings, while pleasures might involve sowing early outdoor crops and harvesting the broccoli, lettuce or beetroot that have been growing over winter.

Although Russell rates her polytunnel highly, she admits they aren't the most attractive things to look at, so as well as giving careful consideration as to where to site it in your garden, be aware that neighbours won't want it blocking their view either. "A polytunnel can remain in place for decades, so it is worth putting it in the right place," she says.

"If it is close to the house, you can pop in and out with ease, but don't put one where it will spoil a view.

"It's a good idea to have a water supply close by and the same goes for electricity if you intend to use propagators. Most polytunnel crops like plenty of sun and the structure will last longer if it is sheltered from strong winds."

Russell says that in an ideal world, you will prepare the ground before putting the structure up. That way you will know if you have chosen a spot that is filled with buried boulders or sits on a layer of clay.

It also means you are less likely to damage the polythene if you use a mechanical cultivator.

"Having said that, time can be a factor and it is probably better to get the structure up on a fine day, when help is on hand, than to delay for months until the beds are dug," she says. "Some people choose to install raised beds once the structure is up, or to use layers of mulch to build up fertility without digging at all."

Once you've got the practicalities out of the way, it's time to start planning what you're going to grow. Russell says that it really is feasible to keep vegetable production going for 12 months of the year, although low temperatures are a factor the further north you get and added coverings may be needed if the winter is really cold.

"Outdoor air temperatures went down to -12C last December, where I live," she says.

"Many crops flopped and looked sorry for themselves for a while, but the following week they all perked up and thrived once temperatures started to rise and none had any extra covering: spring cabbage, kohlrabi, spinach, swiss chard, coriander, rocket, winter lettuce, mibuna, mizuna, turnip tops, broccoli, endive, parsley, lamb's lettuce and beetroot."

Young broad bean plants and mangetout also survived the cold with an extra covering of bubble wrap, and the only real casualties were some late peppers and Florence fennel.

Growing under cover increases your options, but also brings its own set of problems in terms of pests and diseases. Airborne diseases, such as blight, are less likely to be a problem than for outdoor crops, whereas grey mould can be a problem if plants are spaced too close together and if ventilation is limited. Red spider mite can proliferate if it is hot and dry, but this can be dealt with by damping everything down on hot days.

Russell says that there are good organic solutions to most polytunnel problems - the most important thing is to spot the problem and to take action at its earliest stage. So if, for example, greenfly appear you have lots of options: squash them if there are just a couple; take pots outside and spray with a jet of water; introduce a few ladybirds or plant nasturtiums to discourage them.

Whatever problems you encounter, the extended growing season should make up for it. Russell says that each year tends to have one or two outstanding performers and these aren't always the same ones.

"Aubergines can do well one year and only bear one or two fruit in the next. This is usually down to the weather as much as growing technique," she says.

"Tomatoes are usually very reliable and produce a bumper crop whatever the weather outside is like." As for favourites, she highlights the first meal of peas, new potatoes, courgettes, baby carrots, broad beans, and strawberries in late April or early May.

As well as providing a great growing experience, Russell believes that a polytunnel can provide a sheltered refuge for the gardener.

"I know a man who lived in a large polytunnel, along with the crops, while he built his house," she says. "I know others who have deckchairs, baths and patios among the growing plants. These are unusual, but they give an indication of how pleasant it can be inside a polytunnel."

This article was first published in The Scotsman, 19 February, 2011