Guide to Growing Grapes
Wine grapes can successfully be grown outdoors in most cool climates, and many modern varieties are also sweet enough to eat, at least when cooked. True dessert grapes grow best under cover, but you will need space.
How to Grow
Grapevines are fully hardy but prefer a sheltered site away from strong winds and frost pockets. They need full sun to ripen the fruit and are best planted against south-facing walls or fences. Grape vines will grow in a wide range of soils, including chalk, sand, and clay, and will tolerate poor, shallow conditions. Bare root vines should be planted in the winter; container-grown vines can be planted at any time. They need little additional feeding once established, since their long roots dig deep. Being climbing plants, grape vines need support and can grow to be very large. The simplest way is to grow them as cordons. They can be allowed to climb over pergolas but will fruit poorly. Container-grown grapes are widely available in garden centers, but contact specialty nurseries for the best selection.
Certain dessert grapes require long, warm seasons to ripen fully and can only be grown successfully in large greenhouses or sunrooms. Growing grapes indoors requires year-round care, so consider carefully before planting.
Wine grapes are commonly grown outside, although the fruit is often too sour to eat fresh. Use them for cooking or wine making instead.
Dessert grapes are delicious fresh from the vine and can be grown outside if you choose the right varieties. Others must be grown indoors.
Varieties to Try
Grapes ripen green, referred to as white (W), or red (R), depending on variety. Outdoor wine grapes include ‘Barbera’ (R), ‘Chardonnay’ (W), ’Chenin Blanc’ (W), ‘Primitivo’ (R) and ‘Trabbiano’ (W) varieties. On the other hand, outdoor dessert grapes to try include 'Catawba’ (R) and ‘Delaware’ (R) varieties.
Grapes are vigorous climbers and must be trained on a system of horizontal wires in order to have a good crop. There are two different techniques commonly used: The single cordon system, often used indoors, involves a single, 6 feet (2 m) tall stem that is permanently trained upright and pruned to develop a system of fruiting spurs.
In the summer one new shoot is allowed to develop per spur. New growth is trained on wires and bears fruit. Fruited stems are pruned out in the winter.
The double guyot system, most commonly used for outdoor grapes, involves keeping only three stems and removing the rest in the winter. The center stem is pruned to 3–4 buds, the outer two should be carefully bent out horizontally and tied to the wires to grow in the summer.
In the summer new stems develop from the horizontal limbs and bear fruit. At the same time, three new shoots are allowed to develop from the central stem but are not allowed to flower. In the winter when all fruited growth is removed, these three stems are left to start the cycle again.
Thinning and Harvesting
As fruit clusters develop in the summer, they should be thinned to promote healthier, full-sized fruit. Left unthinned, the grapes will be undersized and will not ripen fully. They will also be prone to disease, which could spread to other clusters. To give time to establish, vines should not be allowed to bear fruit for their first two years.
In the summer, use a pair of pruners or round-tipped scissors to carefully thin individual berries. Avoid damaging remaining fruit.
Continue thinning until the bunch is reduced in size by a third. Take the opportunity to remove weak or damaged fruit. Grapes are ready when they are soft, taste sweet, and their skin has taken on a translucent quality. Remove them by cutting through the stem with pruners.
Watch Out for These Pests and Diseases
Birds and wasps may target outdoor vines while the fruits are ripening. Use wire or plastic netting to deter birds, and hang wasp traps nearby.
Botrytis, also known as gray mold, can also be a problem for grapes, causing fungal growth on stems, leaves, and fruit. Fruit often decays before ripening. Destroy all infected material, and prune congested growth to improve air circulation.