The majority of grapes are cultivars of the European grape vine, native to the Mediterranean and Central Asia.
For most of the Country, apart from the South of England, these will be planted in Greenhouses, with the roots outside to ensure easier watering. Although the grape vine is hardy, for most of the Country it needs the extra heat available in a cool greenhouse to ripen the fruit. The vines can grow into very large specimens, if they have the space and are pruned accordingly.
Amazingly, the three largest grape vine specimens in the World, grown under glass, used to be at the Forth Vineyard at Kippen, in Scotland, where I saw them many years ago. The cutting of the grape variety “Gros Colman”, was planted in 1891, and eventually covered an area of 5000 sq ft (465 sq m) in four long greenhouses that stretched for 300 ft. The main stem had a girth of 55 ins and in 1964 the vine produced 3250 bunches of high quality table grapes, before it was cut down to make way for housing. Sacrilege!!
The first commercial outdoor vineyard in Scotland is on the banks of Loch Tay in Perthshire, where they will make a crisp Riesling wine. You need some 100 days of sun and heat to ripen the grapes to make wine. There are already some 416 vineyards in England, mostly in the South.
As most people will grow their vine in a small greenhouse, along with tomatoes, it is better to grow the grapes to eat, rather than to make wine. Position the vine to the rear of the Greenhouse, so that it does not keep the sun off other plants. If growing the vine outside, in the South of the UK, you will get the best results by planting it up against a South facing wall, and train it up wires or a trellis in a cordon system, with a vertical leader and horizontal laterals.
Grapes vines should be planted in the soil, with their roots outside the greenhouse, so that they do not need to be watered. The vines themselves should be trained so that the stem or “rod” is led under the base of the greenhouse into the inside of the greenhouse.
The main stem should be allowed to grow up the inside of the greenhouse until it reaches a wire (fencing wire), hung horizontally about 30 cm below the rafters. The wire should be positioned so that the hanging bunches of grapes are out of the way of your head.
Train the main stem along the horizontal wire until it reaches the other side of the greenhouse. The vine should cling to the wire with tendrils, but can be helped by tying-in with jute twine. Never tie in with wire or polythene twine or it will strangle the stem.
They should be pruned in the Winter, while they are dormant, as they can “bleed” very badly if they are pruned while the sap is rising. You can “pinch” out with finger and thumb, the new soft growth in the Summer quite safely, but the harder older growth must only be pruned while the vine is dormant.
Cultivation for the new year starts in March by lightly sprinkling some quick release fertilizer on the ground around the main stem, which will probably be outside the Greenhouse. The buds will start to break in April, and the tiny flowers will appear in May. While grapes are self-fertile, shake them to fertilize the flowers with the pollen and get a better fruit set.
Only keep one fruiting shoot (lateral) per node, spur or bud, and pinch back the fruiting shoot after two leaves have grown beyond the first flower spike.
Only keep one flower spike for each fruiting shoot, to maximise the size of the remaining grape bunch. Though the season, keep on pinching out any excessive growth with your finger and thumb, otherwise the vine will become a “fankle” of tangled stems.
If the set of the fruit has been good, to get the best sized fruits, it will be necessary to thin the fruitlets with a small pair of scissors, taking out all the smallest grapes and any diseased ones.
Apply a high potash liquid fertilizer every three weeks from fruiting to the grapes colouring. Reduce watering in August to aid ripening of the grapes. The leaves will fall off, probably in November, and the vine becomes dormant in the Winter.
The fruit will be ripe when the grapes change from the green to a yellow green or to a red or dark red, depending on the grape variety. In addition, the grapes will have a slight “give” when gently squeezed between finger and thumb. And you can always taste them! Cut off the bunch of grapes with scissors and carefully place into a padded container for the journey home.
Storage of grapes is best in the cool box of the fridge, where they should last for 2 to 3 weeks. If you have huge quantities of grapes, you could try making wine, but the varieties of vines that you would tend to choose for dessert grapes in a greenhouse, are not those that you would choose for wine making.
Only when the vine has become fully dormant in the middle of the Winter, is it safe to prune the vine back to the main spurs, and remove any excessive growth. There is nothing worse than leaving the pruning too late in the Spring, when the sap has started rising. Dormancy of Vines is ending earlier each year with the milder Winters. January is usually the safest month to carry out pruning. If you leave it too late, then you will watch in horror as the sap spurts out of any pruning cuts you make and it is very difficult to stop the flow of liquid. Apparently vines can bleed to death, through loss of sap. Faced with this situation when the flow of sap had not stopped for several days, I was once forced to improvise and tie on a bandage to stem the flow! A situation not to be recommended!
Pests and diseases. In the greenhouse, the worst pest is red spider mite, which you will need to spray with a pesticide as soon as you spot it.
Be careful to prevent the temperature in the greenhouse rising much above 30 C, as this will “cook” the vines, and they will drop their leaves or even die. They are particularly at risk as they are frequently trained on wires perhaps 30 cm below the glazing in the hottest area of the greenhouse. If you put a min/max thermometer at the same height, you will find that the temperature will readily soar above 35 C on a summer sunny day. You can control the temperature with the use of automatic opening ventilators.
VARIETIES FOR GROWING INDOORS IN A COOL GREENHOUSE.
Black Hamburg This was the traditional choice for a cool greenhouse and ripens well in the West of Scotland. It produces early, dessert, medium sized, sweet and juicy grapes.
Thomson’s Seedless. This green, seedless dessert grape will ripen well in a cool greenhouse.
Flame. This is a dessert, seedless, red grape with a crisp texture. It ripens September or October in a cool greenhouse.
Taking grapevine cuttings is done at the time of the Winter pruning while the grape vine is dormant. Select pencil-thick pieces of one-year old wood, about 30 to 40 cm long, cutting a sloping cut across the lower end of the cutting. This is to ensure that you plant the cuttings the correct way round. Plant the cutting, sloping end first, into a pot filled with moist potting compost and set aside inside your greenhouse. Keep the compost moist and the cutting should root and start sprouting soon after the “mother” vine starts growing. Watch out for vine weevil grubs attacking the roots of the potted cuttings in the Autumn. Once the rooted cutting has been planted out deep in the ground, the roots seem to be immune to vine weevil attack.