Growing Grapes: Greenhouse Planting Guide
Grapes can be cultivated in the most simple, as long as the structure faces south to make use of the maximum amount of sun. The lean-to type of greenhouse is ideal.
Ifare to be grown in the same greenhouse as other plants, the latter should include only those that grow outdoors in summer and require little heat in winter, for vines, certainly at the beginning of their lives, should not be subjected to very high temperatures.
Different varieties of grape require rather different temperatures, but in general the temperature in January should be restricted to a range of 50 to 55° F. (10 to 13° C.). In March the minimum temperature should be raised to 55° F. (13° C.), and from April onward the day temperature should be 70 to 75° F. (21 to 24° C.), dropping to 55° F. (13° C.) at night. When the vines are in bloom the night temperature should not be less than 60° F. (16° C.), although Muscats will need a temperature of 70° F. (21° C). Once the grapes have coloured, reduce the heat to the minimum. During the winter, after the grapes have been picked, the vines will not be harmed if they are exposed to frost.
A buoyant atmosphere is essential for vines. Give generous ventilation at all times, and increase ventilation if the temperature rises. Moisture is also necessary, which means that theshould always be damp. Spray the leaves of the vines occasionally, and the floor and walls of the greenhouse in hot weather.
Although vines are not particular about soil, they require excellent, so always guard against the possibility of stagnant water collecting in the borders. A clay sub-soil is ideal for vines. The border should be up to 10 ft. wide, but since this is seldom possible in a small greenhouse, it is advisable to arrange for the roots of the vine to find their way under the walls of the greenhouse and into a well-prepared border outside. A turfy loam, with the addition of some stable manure and a few broken bricks, makes a suitable soil.
Although vines can be propagated from buds or cuttings, the beginner is advised to buy prepared canes in pots. Wash the roots free from soil so that they can easily be spread out in the new bed, trim the canes back to about 1-1/2 ft., and plant them in January, 3 to 4 ft. apart. Be sure to fill in plenty of soil among the roots, and tread the plants in well.
Apart from keeping the soil evenly moist at all times, vines need thorough watering during specific periods of their development. Water well when the vine is starting to grow vigorously, just before-flowering, when the fruit is setting and again when it is swelling, and finally after the grapes have been harvested.
TRAINING AND PRUNING
Training anda vine is an extremely important operation, but is not difficult. During the first year, the vine will bear no grapes, and only the main shoot should be allowed to grow to its Full length. Stop side shoots when they reach 2 ft., and cut them back completely when pruning in the winter.
A few bunches of grapes may be produced during the second year, for the side shoots are now allowed to develop naturally. In the winter, however, prune them back to one bud from the main stem, leaving the most vigorous spur. The main shoot, too, should be pruned back to the hard, ripe wood, probably about 6 to 8 ft. from the ground. As it needs support tie the vine to wires stretched the length of the house 1 ft. from the glass walls or roof. Gently bend down the laterals before they touch the glass, and tie these to the wires too. Make sure that they are evenly distributed over the available space and receive the maximum amount of light and air.
In the third year, the vine will produce a full crop of grapes, and should continue to yield fruit for many years. Restrict each lateral by nipping it off at two leaves beyond the first bunch of grapes. After the fruit has been harvested, cut each lateral to ‘half its length, and in the winter, prune to one bud from the main stem. The main shoot, too, should now be stopped at the top wire of the house, to encourage fruit-bearing shoots to break lower down.
If only one vine is grown in the green-house, keep two main shoots during the first year, and train them horizontally in opposite directions. The laterals that grow from the upper sides of these shoots should be trained vertically. The subsequent treatment is the same as that described above.
Never allow more than one bunch of grapes to develop on each lateral, and remove any others as soon as possible. As a general rule, each foot of well-matured vine should carry no more than 1 lb. of fruit. It may therefore become necessary to carry out further thinning.
In the case of some heavy-berried vines, the top two or three bunches may-heed to be supported by looping raffia to the wires.
A good bunch of grapes has a compact appearance, and should not be allowed to become too long or straggling. The individual grapes in a bunch may therefore need thinning, particularly at the centre, otherwise those grapes will become flattened. Never touch the fruit by hand, but hold the bunch steady with a short, forked stick and use special grape-thinning scissors.
The following varieties are recommended for cultivation under glass:
Black Hamburgh, May to November; very productive, excellent flavour.
Lady Downes, December; keeps well.
Cannon Hall Muscat, December; good flavour.
Muscat of Alexandria, May to December; excellent flavour.