Methods of Protecting Vegetables
‘From first to last gardening in this country is a continuous conflict with difficulties.’ So wrote the Victorian gardening writer Shirley Hibberd in 1877. Little has changed, because the main source of the conflict, now as then, is the short growing season allowed by our fickle climate.
Most of our vegetable crops start to grow when the average daytime temperature reaches 6°C (43°F) in spring and stop growing when it falls below this temperature in autumn. The number of ‘growing days’ any gardener has at his disposal depends entirely on where he lives. The main purpose of ‘protection’ — which embraces anything from cloches to frames to greenhouses and includes both the low and the newer ‘walk-in’ polythene tunnels — is to increase the number of these growing days. There is no doubt that a little protection of some kind, however makeshift, pays enormous dividends in the kitchen garden.
Reasons for Protection
It raises theand air temperature extending both the growing season and the range of crops.
Only with protection can borderline crops such as tomatoes, green peppers and melons be grown successfully, whatever the season.
It shields crops against the elements — rain, hail, salt spray in maritime areas and, most important of all, wind, thus improving both the yield and quality of vegetables. Protection is especially worthwhile against the lethal combination of cold winds and low temperatures.
It reduces bird damage in the garden. In some circumstances birds do more damage than any other outside agent, including pests, diseases and climatic extremes. Their repertoire ranges from sparrows eliminating alland to pigeons plundering the winter greens.
It gives some defence against frost, although this is only complete when the protection is heated in some way. Frames, for example, can be electrically heated with soil cables.
It keeps crops clean, which means less wastage and, as a bonus, less vulnerability to the manywhich are encouraged by ‘mucky’ plants.
Apart from enabling us to grow more crops of a better quality over a longer period, protection is useful for all sorts of odd purposes, which include warming up the soil before sowing, hardening off seedlings and young plants, ripening tomatoes and drying off.
What Kind of Protection
The sort of protection to choose depends on the size of your pocket as much as the size of your garden. Should you go for something permanent, like a traditional greenhouse? Or should it be semi-permanent, a ‘walk-in’ tunnel or greenhouse clad with polythene film? (These require no foundations as the edges are simply anchored with soil.) Or do you really want a temporary, mobile device such as a portable frame or set of cloches?
The important point about any permanent structure is that if the same crop — tomatoes or, for example — is grown for several years in the same soil, there is a build-up of pests and diseases which results in soil sickness, making it impossible to continue growing the crop. The only remedy is to change or sterilize the soil, or to grow future crops in some form of container such as growing bags, boxes or pots, or in a soilless system such as ring culture.
The other important consideration is the covering material. Glass transmits light best, retains more heat at night and does not deteriorate with age; on the other hand, it is very expensive, heavy to erect and there is the risk of breakages.
Some of the modern rigid and semi-rigid plastic materials are cheaper, transmit light reasonably enough (plants grow surprisingly well under the diffused light of some of the translucent materials such as Correx), but they lose heat more rapidly at night. Many plastics deteriorate within three to five years due to ultra-violet radiation, becoming discoloured and brittle. Polythene films are cheaper still, though the least durable. Thin films (150 gauge) are used over small hoops to make low tunnels (the cheapest form of protection for a vegetable garden) while heavier film (600 gauge) is used to cover the large galvanized steel hoops of walk-in tunnels, or structures made in the traditional greenhouse shape. All of these cheaper alternatives have much to offer the amateur vegetable grower.
To get most out of protective systems:
- Put cloches, frames or polythene structures on the best available soil — fertile, rich in , well-drained and weed-free.
- Anchor cloches, the lids of frames and low polythene tunnels as securely as possible, or they may blow away or be damaged in high winds. Where cloches have a small hoop on the top, run a string through the hoops and anchor it to stout stakes in the ground at either end.
- Close the ends of cloches, for example with panes of glass; otherwise a chilling wind tunnel is created. This also helps to keep out the birds.
- When using polythene film to make tunnels, frames or cloches: Bind any rough edges on the framework, whether it is of wood or steel, with cloth or tape. This may give the film an extra year of life.
- Mend any tears with plastic tape.
- Put the film over the structure on a warm day, so that it can be pulled taut. Flapping film is subject to wear and tear. Plastic can be battened to a wooden frame to make it more rigid.
- Make sure there is adequate ventilation. If possible put a door at either end of any structure more than about 6m (20ft) long, with screen netting in one half of the door; or cut holes the size of dinner plates about 45cm (18in) above ground level at either end. Tape a piece of polythene over the holes in winter.
- Get longer-lasting ultra-violet treated film or plastics wherever possible.