It is easy to regard grapes as an exotic crop for the greenhouse, and to some extent this is true if large dessert berries are desired. But in many parts of the country, particularly regions in the south, a good crop can be obtained outdoors. If the right varieties are chosen these are usually excellent for eating and for wine-making.
VINES UNDER GLASS
The easiest method is to trainas single cordons, that is with a permanent single stem called a rod, from which side shoots grow each year and bear the bunches of grapes. As the best grapes grow on a current year’s shoot, arising from the stub of one pruned the previous year, the method has this end in view.
Young vines are usually planted just outside the greenhouse or conservatory and the main stem taken through a gap in the wall into the house. This is done to provide better conditions for the roots. If it is more convenient, the vine can be planted in the greenhouse but more watering will be required and this could be a problem during holidays.
A supporting system of horizontal wires is necessary. They must be 23 cm (9 in) apart and the same distance below the glass to avoid leaf scorching. The vine is planted in winter and cut hard back. The following growing season the strongest young shoot is allowed to grow up towards the apex of the house and the others are rubbed out. This leader will produce laterals (side shoots) and these are pinched out at the tip when 45-60 in (18-24 in) long. Sub-laterals (side shoots from the laterals) are pinched when they have produced one leaf. It is important to space the laterals carefully so they are about 45 cm (18 in) apart on alternate sides of the main stem. Badly placed or additional laterals must be removed while they are young enough to be rubbed out.
The vine will be ready for its first annual pruning when the leaves change colour in autumn, just before they fall. Although the rod may have reached the top of the greenhouse in the first year, it should be cut back to a bud where the shoot it is well ripened. Cut back the laterals on the rod to one or two buds in order to build up a spur system. The following year one other shoot is allowed to continue extension growth until the roof area has been filled. Laterals are selected on alternate sides every 45 cm (18 in) and stopped as before. Once this main shoot has grown to its maximum extent it is treated as a lateral.
Returning to the laterals that were cut back to spurs the previous autumn, these will produce new shoots in spring which, when 2.5—5 cm (1—2 in) long, are reduced to two per spur by rubbing the rest out. If the lowest spurs are slow to produce new growths, spray the rod with warm water on sunny days, untie it from its supports and arch it down close to the ground until growth can be seen.
As they grow, tie the selected laterals to the framework of wires. Flower trusses will soon start to form on them, and further growth is then pinched out at two to four leaves beyond the truss. Sub-laterals are stopped at one leaf. It is usually necessary to reduce the number of bunches so that remaining grapes will swell to a good size. Some can be removed when theare seen to have set, the remainder when the grapes have started to swell. As a guide, work to the formula of one bunch to 23 cm (9in) of rod. So that each bunch is not overcrowded, cut out some of the berries with a fine pointed pair of scissors. The remainder will be larger as a result. Of course, grapes for wine-making need not be thinned as much as those for the table.
The final job in the year’s programme is to cut the laterals back to about two buds in autumn, leaving only short spurs along the main rod.
A south- or south-west-facing wall is an ideal place to grow a vine. A suitable shape is a fan tied to horizontal wires with two or three main rods carrying laterals, Training is the same as for vines under glass, except that initially two or three main shoots are allowed to grow. As before, a spur system is built up with laterals cut back close to the main rods in autumn.
Vines can also be grown in rows under the large barn cloches, and pruning is largely the same except that two new shoots are required each year. One wire only is needed, 23 cm (9 in) above the ground. One shoot is shortened to eight buds and tied to the wire, while the other is cut back to two buds. These two buds will produce the replacement shoots. Cloches are put over the row in summer. Grapes are produced on the laterals that grow from the shoots tied to the wire. Stop these laterals at two leaves beyond the bunches.