This section is from the book "The Gardener V3", 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.
Having shown that a lean-to vinery facing due south is the best form for early forcing, under this head I have no hesitation in saying that for the same reasons that I have recommended the lean-to for winter forcing, when the sun is only a short time above the horizon, the span-roofed vinery running north and south is best for the ripening of Grapes, say after the middle of July. A span-roofed house in this position gets the benefit of sunshine longer in summer than does the lean-to. The east side gets the morning sun, at noon the whole roof is exposed to it, and on till late in the evening the west side is exposed to the sun, when it would merely be shining on the end of a lean-to. Besides this, a span-roofed house, from 20 to 24 feet wide, encloses a larger volume of air than a lean-to of the same width, and this is of much importance in Vine-culture. In large airy houses Grapes are better flavoured, are more fleshy, and consequently hang better through the winter. After considerable experience in Grape-growing in lean-to houses, ranging from 6 feet wide to what may be termed large airy vineries, I unhesitatingly recommend that they be built large and roomy.
Besides the reasons already named, large vineries can be fired to a given temperature more steadily than small ones, because a large volume of air is not so easily influenced by external variations of temperature, just the same as a thin wedge of iron is sooner heated and sooner cooled than a thick one. Fig. 18 represents a span-roofed vinery of the dimensions I recommend for ripening Grapes late in summer and autumn to hang through the winter.
A drain runs in the draining material from the front to the back of he border, terminating in an upright shaft just below the hot-water pipes at the back of the vinery and at the front of the outside border, thus communicating with the external atmosphere and that of the vinery.
These drains should be constructed 6 feet apart the whole length of the border, and be open-jointed, so that the air from them can find its way right and left among the open rubble, which should form the lower stratum of the drainage. This is for the purpose of what has been termed aeration, which means the exposure of the soil to the air from under-currents. No doubt, for summer forcing, it is beneficial, especially in wet climates, to open the mouths of the upright shafts in hot sunny weather, thus admitting warm air underneath the border.
It is a very common error to fix the wires to which the vines are tied too near the glass; they should be not less than 16 inches from the glass, to allow a free circulation of air between it and the foliage.
It is scarcely necessary to point out the evil of having the foliage in close contact with the glass. The wires should be fixed at 1 foot apart.
The first thing that should be thought of and most effectively secured in the making of borders is drainage; for however great the skill otherwise brought to bear on the after-management of the Vine, first-rate results need not be looked for if the roots are subject to stagnant water. One of the most important points in successful Grape-growing, is the preservation in winter of the young roots made in summer, which is impossible if the border is subject to stagnant water. Of course the extent and character of the drainage necessary has to be determined by the position of the vinery, the nature of the subsoil, and to some extent by the average amount of rain which is peculiar to the district. The amount of drainage necessary on the retentive clay of such as Middlesex, or in the Lower Ward of Lanarkshire, the Dumfries or Argyle coasts, where so much rain falls, would be superfluous on the rocks of some parts of Somerset, or on the generally dry soils of East Lothian. By these conditions should also be decided to what extent borders should be elevated above the natural ground-level.
In preparing the site and drainage on damp retentive subsoils, let all the natural soil be excavated to the depth of 4 feet from the bottom of the arches or lintels at the front of the vinery, and supposing that the outside border is to be 20 feet wide, give it a slope of 18 inches to the extremity of the border. The site for the inside border should be sloped to the same extent, upwards in the case of a lean-to house, to the back wall. Lay down a layer of concrete, 3 to 4 inches thick, over the whole site of the border. Run a main drain parallel with the border at its extreme front, and 6 inches below the lowest level of the concrete. In order to make sure of the most perfect drainage, lay tile-drains at right angles with this main drain, up to the back of the vinery, at every 8 feet. Over the whole surface of the concrete, and covering the tile-drains, spread a layer of broken bricks, road-metal, or round gravel with all sand sifted out of it, to the depth of 8 inches. Finish off with a sprinkling of smaller gravel, and a turf, grassy side downwards, over the whole surface. The site is thus ready for the border.
The slope of the site, and soil, drains, etc, can be seen at a glance in fig. 18.
On what may be termed healthy gravelly subsoils in dry localities, where water neither stands nor rises, such extra care in drainage is not absolutely necessary. But where there is the least chance of there not being a ready and immediate escape for water, no hesitation should ever be allowed as to the necessity of draining as has been directed. I have never seen Vines do well in wet, and as a consequence cold borders, and know of instances where wet and unproductive borders have been rendered fruitful by perfect drainage. Although the Vine in a growing state requires much moisture, it will not put up with stagnant water at any season.