This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
In 1865 I was anxious to prepare a quantity of extra strong young Vines in large pots, and not being very well off for a place to grow them in, they were put into a Muscat-house with a high temperature. This was after they had been shifted into 14-inch pots. Under circumstances over which, unfortunately, I could have no control, they were allowed to remain in said house till the Muscats completely covered the roofs of the vinery, and became gradually weaker and weaker from the want of light and air, so that they looked more like being sent to the rubbish-heap than ever becoming Vines that would bear a crop the following year. I, however, decided to cut them down to within a bud or two of the surface of the pot, and had them placed in a light house with a night temperature of 70°, with 15° to 20° more with sun-heat by day. Water was sparingly applied, and they very soon burst their main buds, which, under ordinary circumstances, would not have moved till the following year. They came away with amazing vigour, and made magnificent Vines 10 feet long - the strongest I ever had under my care.
This season, on the 16th March, I planted a house of Muscats, and the last week of May, after they had made fine growths 8 and 9 feet long, these were cut down as described above. They likewise soon burst their main buds, and are now twice as strong as they were when the same length in their first growth. And where Vines planted one year are required to yield the finest possible crop the year following, I would strongly recommend this two-growths-in-one-season system as one that will produce a more vigorous Vine of a given length than if allowed to grow on at first.
All gardeners who have had the charge of Vines can scarcely fail to have observed how very strongly a Vine in a green unripened state, when growing vigorously, bursts its main buds when the laterals are closely stopped; and the same increase of dimensions takes place when a young Vine is cut down as I have described. It is necessary, however, in order to get season sufficient to ripen the second growth thoroughly, that the Vines be planted in March, and that the cultivator have a good command of heat in the case of Muscats especially.