Standards.—These must be planted, when other crops are to be grown beneath. Quincunx fashion :·: is the best. The rows, as a rule, should be 24 feet apart, and the trees in each row about 20 feet. Plums do not shade as much as apples and pears, yet it is always wise to avoid overcrowding. Some sorts are not as spreading or as vigorous as others. Weak growers like the Early Prolific might be placed between Jefferson and Monarch. Good trees in six or seven years should bring good returns, but the intermediate space may meanwhile be utilised for strawberries, gooseberries, and so on. Standards should be 6 feet high or more. After planting, cut back the shoots to about one-third of their length, the weakest still more, to promote vigorous growth, and cut just above an outer eye. Keep the centre open. In later years stop gross or robber shoots in June, clipping some leaves of the latter, if necessary. Never allow boughs to cross, and keep all the tree fairly open. When the tree begins to bear, little pruning is necessary. But stopping luxuriant shoots about midsummer is good for the other branches, and for the production of fruit buds before winter. Complete pruning early in August. In winter cut out dead wood, and shorten boughs wherever fresh wood is required. The wood of the Victoria plum is very brittle, and requires special treatment. Shorten the strong growing luxuriant branches of this variety in July; otherwise later on they will break when loaded with fruit. Messrs Bunyard's choice of six for market standards is: Rivers' Early Prolific, Czar, Early Orleans, Victoria, Pond's Seedling, Rivers' Monarch.
Half Standards (3½ feet to 4 feet high) are better, and more manageable. Planted 12 feet apart, gooseberries, etc., may be placed around them; otherwise they may be nearer, even up to 6 or 8 feet. These should be pruned in August unless strong shoots require pinching back. Stop new side shoots at the sixth leaf to produce fruit-buds. Avoid excess. Wounds made in August have a better chance of healing while the sap is still active. Pyramids are not as useful as bushes; the former require a central stem and special training.
In Bushes, keep the tree open, stop strong shoots at midsummer, prune new (side) shoots back to six leaves about mid-August, and take out wood that is not wanted, admitting the sun and air. In winter cut back any boughs where fresh shoots are wanted to a wood bud at an outer eye.
Trees on Walls.—Plums are usually put on east walls, but the best repay a south as well as a west aspect. They require and repay care and skill in training. If the wall is low, the horizontal form is best. The branches should be taken several inches below the line along which they are to be trained, and not at right angles; the sap will flow better, and the tendency of branches to die off will be lessened. The first branch should be 1 foot from the ground, the rest 9 inches apart. Coarse stems and branches must be avoided by moderate root-pruning. The wood must be kept near the wall, that wood and fruit may be better ripened. The fan system is better for a high wall. Train shoots on the tree from the nursery in regular order at equal intervals, cutting back only to ripe wood. Pick off growths on the side next the wall, and others badly placed. Lay in new wood every year, and in August or Early September cut out unsightly branches or spurs if there is other wood to replace them. Prune upper part of tree first, and encourage foliage and fruit spurs over every part. Stop strong growing branches at midsummer, and pinch back side shoots to six leaves about mid-August. Fruit buds will follow. Wire on the wall should be 1½ inch out, with an interval of 1 foot between each wire.
Manures
The absence of moisture and the consequent exhaustion have a serious effect on plums, and should never be allowed. Mulch newly-planted trees in light or poor soil; give liquid manure or irrigate in dry weather. Should the crops be heavy, and the soil at all deficient in lime, the deficiency should be made up by scattering lime some distance around the stems and working it gently in. "An annual dressing of decayed vegetable matter, old manure and lime-rubbish, laid about a yard round the stems, produces very satisfactory results" ("Plums for profit"). Supply this in November. The artificials recommended by R.H.S. for pears are also good for plums. Dr Griffiths recommends cow dung and a mixed manure, composed of 5 parts of kainit, 1 part of magnesium sulphate, 2 parts of superphosphate; 7 lbs. of the mixture to be applied to each tree in autumn, two more pounds in the spring.
Established trees in full health need no aid in an ordinary season if they carry no crop. Damsons should be fed as well as plums.
Thinning
must be carried out severely if the crop is thick. In a good plum season, only very fine and first-rate fruits fetch a good price, and these can only be obtained by thinning the fruit and feeding the trees. An annual crop (if frost does not interfere) may then be expected. Half the crop in some years should be taken off long before the fruit is ripe. The jam-makers utilise green and half-ripe plums.
Gages