Step-by-Step Guide to Growing Greenhouse Grapes
Dessert, greenhouse grapes are normally varieties of Vitis vinifera (fam. Vitaceae) Deciduous vine, with a long life of hundreds of years.
Planting to harvesting time: 3 years.
Size: growing to 27 m (60’) in the wild and to equivalent lengths in old specialized vineries; normally kept to a long rod 3.5-5 m (12-16’) in the greenhouse.
Yield: a long rod, 3.5-5 m (12-16’) long, will produce 10-12 bunches per year.
Grapes are usually considered to be a warm climate fruit, and it is true that they prefer long, hot summers in order to ripen fully. Nevertheless, the best quality dessert grapes are grown in greenhouses in temperate climates. These shy-setting varieties, particularly the ‘Muscats’, set fruit best in the artificial conditions of a greenhouse. Although you can grow wine varieties in a greenhouse, it is much more sensible to use your greenhouse for the sweeter and more delicate dessert varieties, producing high quality grapes which you would not be able to grow successfully outdoors.
Unfortunately, grapes dislike the growing conditions preferred by most other greenhouse crops, such as tomatoes and. To get first-class grapes, you really need a specialized vinery where an ideal environment can be maintained. But do not worry if you cannot afford to devote a whole green- house to grapes; you should succeed in producing moderate crops of all but the most delicate varieties in the normal, home gardener’s mixed greenhouse. Once established, a vine will produce good crops for a modicum of effort. A single vine, trained as a long rod, will give you a bunch of grapes every week for three months.
Preparing the Border for Vines
Vines like to spread their roots, but you will get heavier crops if you restrict this tendency; if you allow the root free rein, the vine will produce a lot of vegetative growth at the expense of fruit. By confining the roots to a prepared border, you can better regulate the amount of water and nutrients the plants receive. The traditional treatment of a vine border is to increase its size gradually as the vine grows older and bigger. This is definitely the best way of growing greenhouse grapes, as it ensures a balance between root and shoots throughout the life of the vine, and prevents the nearbybecoming ‘sour’ and infertile. The traditional preparation of a vine border takes much time and effort, but is well worth it, and skimping on border preparation can never be ‘made good’ once the vines have been planted. Good drainage is the most essential feature of a satisfactory vine border. If you are planting the vines indoors, the border should ideally be about 1.5 m by 3 m (5’ x 10’) for each vine, although you can produce quite good grapes with smaller borders. Dig out the soil to a depth of 75 cm (2V), keeping the topsoil and subsoil separate, and fill the bottom with 15-25 cm (6-9”) of rubble to provide a drainage layer.
Cover this layer either with turves laid upside down, or with about 15 cm (6”) depth of straw, to prevent the soil percolating down into the drainage layer and blocking it. Then return the soil to the border, mixing it with two 12 L (2-½ gal) buckets of rotted manure and 120 g (4 oz) of bonemeal per plant, making sure that the topsoil goes back on top. Tread the soil down lightly as it is returned, so there is not too much subsidence later. Border preparation should be done two to three months before planting, to give the soil time to settle naturally.
If your greenhouse space is limited, and you wish to grow other plants as well as grapes, then it is a better idea not to plant the vine indoors at all, but to plant it outdoors and train the above-ground portion into the greenhouse through a hole in the wall. Although vine roots appreciate the cooler temperatures of outdoor life, the cropping will probably not be as heavy as completely indoor-grown grapes, because you cannot really restrict the root run to any extent.
Remove a brick from the greenhouse wall at ground level where you want the vine to enter; temporarily block the hole with straw or newspaper until you come to train the vine through it. Then prepare the outside border as you would for an inside border.