Grapes grow best in areas where the spring is dry, the summer is hot and the winter is cold. In our recent past spring is damp, the summer is flooded and the winter is mild, but with a little shelter there’s no reason why this vigorous climbing plant can’t be grown with great success.
You need to remember that whatever pruning regime you use, you need to have some shoots that, this year, will grow leaves but no fruit, so that next year they can produce fruit. All pruning takes place at the end of the season when the plant isn’t actively growing. If your tunnel or greenhouse is heated you are best to grow grapes as standards in large tubs so they can be placed in the cold.
There are a number of culture systems based on making either a single stem (cordon) or a double one. The vines are either trained on a vertical wire system, so that the wires are at heights of 30 cm to support the cordons, or a single wire in the top of a greenhouse or tunnel.
Plant your vine outside the tunnel and train the vine through the plastic (or a hole in the greenhouse glass) to the inside. Allow it to grow unhindered.
The soil should be well dug and mixed with plenty of well-rotted manure and compost.
Traditionally vines were planted above a rotting dead sheep.
Stake the vine outside and attach a wire to a frame indoors, along which you will train the plant.
In the summer of the first year allow the plant to grow, and pinch back any lateral shoots to around five leaves.
When the leaves have fallen off in the winter, cut back the main shoot by just a little more than half and cut the laterals to a single bud each.
The following summer treat the plant like you did the previous summer; tie in the main shoot and build your frame of wires. Take out any flowers that form. IMAGE: gra5.jpg
The following winter cut the main shoot back to old wood and the laterals to a strong bud each.
So in effect you have strengthened and prepared your plant ready for producing laterals that you will now tie in the following spring and summer.
The buds will then grow out, and the resultant growth is trained along the wires.
The third summer allow one bunch of grapes per lateral shoot to form, and any sub-laterals that form keep to a single leaf. In the winter, when the grapes are taken and the leaves have fallen, cut the laterals to two buds. It is these buds you will use next year and so on.
In our next feature on grapes we will look double cordons and at the Guyot system of culture which is used on commercial growing and outdoor systems.
Indoor vines do well if they are fed with tomato fertiliser each month from a couple of weeks after they have burst into life in the spring until the grapes are ready for picking. Since the bark is fibrous, all kinds of pests over-winter and so scrape the bark away inside the tunnel or greenhouse.
If you are growing grapes in Scotland then it’s a good idea to heat the greenhouse to 4ºC from mid-winter onwards. This will give them a good head start.
The big problem with grapes is that they are full of sugar and unless you have good ventilation between the berries, penicillium fungi will infect the bunches. You can use scissors (some growers have special scissors just for the purpose) to thin out the berries so that the others can grow unencumbered and a good air-flow around the grapes is achieved.
The cardinal rule on harvesting is to cut off the piece of lateral they are growing from so that you do not have to touch the grapes and either contaminate or damage them.
We have already spoken of fungal infection. It comes in three forms:
Botrytis occurs in wet conditions and is kept at bay by good pruning.
Downy mildew occurs where the temperature is really hot and the greenhouse or tunnel is very humid.
Powdery mildew forms on the leaves and fruit. You can prune it away, keep the tunnel or greenhouse really clean and spray with Bordeaux Mixture, developed by French monks just for this purpose three hundred years ago and is still considered to be an organic cure by many.