This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Next to the Apple the Plum is the most important fruit crop in the British Islands. According to the most recent returns of the Board of Agriculture (1911) about 17,000 ac. are devoted to the industry. Of these there are 16,418 ac. in England alone, Scotland having 291 ac, Ireland about 220 ac, and Wales 77 ac The largest plum-growing counties in England are Worcester with 3815 ac, Kent with 3269 ac, Cambridge with 1577 ac, Gloucester with 1141 ac, Middlesex with 691 ac, and Bucks with 570 ac. Reckoning fairly close planting at 250 trees to the acre, this would give something like 4 1/4 million Plum trees for the United Kingdom. Taking the average crop of 2 bus. of plums per tree, 500 bus. would be the crop for 1 ac; and at 6s. per bushel this gives £150 per acre. This figure is probably never reached in practice, but Mr. Bunyard in his Fruit Fanning for Profit gives £112 as the gross return for 1 ac. of standard Plums yielding 7 tons. This works out at about 9s. per bushel of 60 lb., or £16 per ton (each bushel holding about 1000 fruits), and only gives an average yield of a little over 1 bus. to each tree at 250 to the acre. When a larger number than this is planted to the acre, the average yield per tree is of course lower in proportion. Taking good and bad seasons together the gross returns for 1 ac. of Plums may be taken at from £60 to £80, out of which rent, rates, taxes, labour, marketing, etc, must be paid. It must be remembered, however, that one or two severe frosts in April or May will reduce the Plum crop almost to nothing in some seasons. [J. W.]
The attention which of late years has been given to the Plum has made it a much more valuable article to the market grower than it was formerly. To begin with, the season has been materially lengthened by the introduction of new varieties, and many of the old shy-bearing varieties have been displaced by introductions that are good croppers. The increase in the popular use of jam has added another factor to the utility of the Plum. Soils that will grow Apples and Pears will grow Plums. On the lighter warmer soils they will come earlier than on heavy ones; but in dry seasons the latter will bring their fruit to normal size when the former will not. Plums readily show the advantage of leaving the wood uncut when planted. After being pruned during the first winter from planting they will throw up strong shoots that, properly treated, will make a good foundation for the future tree. The shoots require cutting back each year, for four years, to one - third the growth, making the cut just above an outside bud; afterwards they may be allowed to grow, only dead or broken branches and cross pieces that rub against others to be taken out. Some heavy-bearing varieties will prune themselves with broken boughs every third or fourth year. If Plums are planted in alternate rows with Apples or Pears they should be 18 ft. by 15 ft. apart. If planted by themselves, the distance can be decreased to 15 ft. by 12 ft. for some sorts, such as Czar.
The preparations for planting, and the remarks as to under-cropping made in reference to Apples and Pears, will apply to Plums also. Half-standard is the best style in which to plant Plums. Let not the planter be tempted to buy old trees because they are larger; two years is quite old enough.