Training and Pruning Vines
With greenhouse-grown vines, you are aiming to produce one, or occasionally two permanent woody stems, called rods. This rod should be trained until it is about 60 cm (2’) from what is going to be the maximum height of the vine—this is the greenhouse ridge in a span house or the end wall in a small ridge house—and then cut off, or stopped. Sideshoots produced by the permanent rod, eventually called spurs, are also stopped, just two buds from the permanent rod. On an established vine, the grapes and leaves are produced on the sideshoots, which are cut back each year, so building up a fruit spur; cutting back is done after the fruit has been picked.
In the first spring after planting, your vine will produce sideshoots from the cut-back main stem. Pick the strongest one of these and rub out all the others with your thumb; this is most easily done when the sideshoots are still tiny. The surviving shoot is going to become your permanent rod; tie it vertically to the cane.
After a while, sideshoots will develop on the permanent rod and these should be allowed to grow until they are about 45-60 cm (18-24”) long, when they should be stopped just above a leaf.
Pick the strongest sideshoots, spaced alternately on either side of the permanent rod, with a gap of about 45 cm (18”) between two shoots on the same side. Tie the selected shoots to the training wires and prune off all the others. These selected shoots are going to become the spurs on which the fruiting laterals are formed. Any sub-sideshoots should be reduced to one or two leaves only. Cut them off just above a leaf.
The permanent rod should be allowed to grow freely, until it reaches the limit of its allocated space—that is 60 cm (2’) from the greenhouse or end wall—when it should be stopped just above the nearest convenient leaf. After this has been done, sideshoots and sub-sideshoots can be allowed to grow freely until the end of summer. Tendrils and embryo flower buds must be rubbed out ruthlessly when still tiny. You need to channel all the strength of the plant into producing the permanent rod and spurs. The main rod and subsidiary sideshoots will all need tying at least once a week, to ensure straight stems, and stopping will need to be done frequently.
In the autumn, when the leaves have turned brown, but have not yet fallen, prune the permanent rod back to between half and two-thirds of its original length, and prune the sideshoots to leave one or two buds on each. It is important to prune early in the autumn rather than in the winter, otherwise the cut stem surfaces will ‘bleed’, as the sap begins to rise near the time of new growth.
In the following spring the vine will produce shoots from all the dormant buds. Allow the strongest shoot at the tip of the permanent rod, and the strongest shoots from each spur, to grow on; rub out all the others, including any produced below the first wire. Allow the new permanent rod to continue until it reaches 60 cm (2’) from the end of the space allotted for the vine, as before, and then cut off its tip once more.
Tie the sideshoots produced from the embryo spurs to the training wires with fillis or raffia; do this as gently as possible. If any shoots are a long way from the wires, do not attempt to tie them all the way to the wire at once. Instead, tie them loosely with a loop of raffia to begin with, gradually tightening this loop over a period of weeks. If you tie the sideshoots down too fiercely at one go, you risk breaking them, and possibly damaging the spur as well. Stop them at a maximum of 60 cm (2’) in length, as before, and allow to grow freely once the main shoot reaches its maximum length.
Sideshoots produced on the new part of the permanent rod should be treated the same way as the sideshoots were treated in the previous year and pruned to produce spurs. As before, sub-sideshoots produced on the laterals should be cut back to one or two leaves.
If the vine is growing strongly, two or three fruit bunches can be allowed to develop on the lower part of the vine; pinch off all other fruit bunches and tendrils. If you allow more than three fruit bunches to mature, you will overtax the vine.
At the end of the second summer, you will very nearly have finished training your vine. Cut back the new sideshoots so that there are one or two buds left on each, and reduce the new growth of the permanent rod by about a third.
In the following spring, select the strongest shoot at the tip of the permanent rod and let it grow until it reaches the maximum length allowed. Sideshoots produced along this final piece of permanent rod are pruned to produce spurs as before; next year treat them as established wood. Sideshoots produced on spurs on the two and three year old parts of the permanent rod are pruned as established wood now.
Routine pruning of established vines is as follows: in early winter prune off any new growth at the end of the permanent rod and cut back the new shoots on the spurs to two buds. In the spring, rub out one sideshoot at each spur, leaving the stronger, when the shoots are about 2.5 cm (1”) long. Additionally, leave one growing at the end of the permanent rod. In the summer, prune off all sideshoots, either above the second leaf after a fruit bunch, if they have produced one, or above the sixth leaf on the shoot if they have not. Tie the sideshoots to the wires. Pinch out all sub-shoots produced on the sideshoots and all the tendrils.
A vine trained in this way should continue to produce sideshoots on the spurs for many years, although the spurs themselves will become very gnarled. Vines trained horizontally in a lean-to greenhouse are treated in exactly the same way except that the sideshoots are trained vertically upwards from the permanent rod instead of horizontally. Promoting bud burst One of the problems of growing vertically trained vines is that buds at the top of the permanent rod near the glass tend to burst first and then sap most of the strength of the vine at the expense of the buds at the base of the plant. To promote an even bud break, the vine should be taken down from the wires during the winter and laid gently on the border; this encourages buds at the bottom of the vine to burst. As soon as they do, tie the vine back up to the wires; this encourages buds higher up the vine to begin sprouting in their turn.
Start promoting bud burst in late winter. Close the ventilators, opening them only when the temperature rises above 10°C (50°F), and syringe the plants with tepid water at mid-morning and again during the late afternooon. Do this on sunny days only. In addition, try to maintain a moist atmosphere on such days by damping down the walls, path and border.
You do not want the atmosphere to become too damp, however, so never syringe or damp down on dull days. Once the buds break, stop syringing the plants but continue damping down.