This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Another point in potato culture intimately associated with the distance given between the rows and sets is the question of earthing up, and the direction. In experiments carried out with "Myatt's Early Ashleaf" it was shown that a greater yield, fewer chats, and better samples were obtained from sets planted 3 ft. apart every way than from 2 ft. apart. To see whether there was any difference between moulding up the rows north and south and rows east and west another experiment was carried out under identical conditions. The sets were 3 ft. apart every way, the only difference being that in one case the earth was drawn up in ridges running north and south, and in the other east and west, with the following results: -
Distance between Rows and Sets.
Total per rod.
Weight per rod.
Total per acre.
North and south
3 ft. by 3 ft.
East and west
3 ft, by 3 ft.
From this it will be seen that such an operation as earthing up may mean a profit or loss to the grower according to the way it is done. Although the sets were 3 ft. apart every way, the fact that the rows were moulded up east and west instead of north and south meant a loss at the rate of 2 tons to the acre, and a worse sample into the bargain. The reason of course is quite plain. By earthing up north and south the rows are fully exposed on both sides to the sunshine at midday, when the work of assimilating carbonic acid gas from the atmosphere is going on rapidly to make tissue and tubers. The soil is also warmed on both sides, and providing it contains sufficient moisture and soluble food the best results may be anticipated. By earthing the rows up east and west, however, the grower is distinctly taking money out of his own pocket, as the experiment shows. At midday only one side - the south - of the rows catches the sunshine, while the other side - the north - is in perpetual shade. Not only is this the fact, but all rows after the first one may be said to be more or less deeply shaded on the south side also. Hence but very little warmth from the sun reaches the soil, and, the genial warmth so essential to growth being lacking, the root action is poor in consequence, and less food is taken up to the leaf cells to be acted upon by the light.
The Dutch scientist Jan van Ingenhousz, who published his researches in 1779, was the first to discover that all green-leaved plants fed upon the carbon in the air during the daytime by means of the millions of minute pores or stomata on their leaves; but very few practical growers appear to have taken advantage of the knowledge which has since been at their disposal. The facts and figures given above show that not only is a fair amount of air and light essential to good growth, but it will pay the cultivator to bear this knowledge well in mind when planting any crop. With such an important crop as Potatoes, hundreds of thousands of pounds are lost every year simply because a man thinks he would be "wasting ground" by planting his sets 3 ft. apart. The reverse is really the case, and growers will find it to their advantage in many ways to give their potato crops more room than is at present customary.