This section is from the book "The Gardener's Monthly And Horticulturist V25", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
This is an operation which every beginner considers himself skilled in, but which is, nevertheless, often badly performed even by practical gardeners. The first point to be noticed is properly draining the pots. When a suitable outlet for the superfluous water is not made it is hopeless to expect success, for no plant can thrive in sour soil. In draining the smallest sized pots one crock (piece of broken pot) over the hole in the bottom, with the concave side downwards, covered with the roughest of the soil, is generally enough. Indeed, a little rough soil in the case of strong-growing, strong-rooting plants is often enough. For plants in 6-six pots one large crock covered with rough lumpy soil may be enough for Balsams, or even Fuchsias, when growing rapidly. For Heaths and plants of a similar nature, small crocks carefully arranged to the depth of fully an inch should cover the central one, and over the small crocks a little moss, or the fibre from the peat or loam, is necessary to prevent the soil stopping the drainage.
For a 12-inch pot from three to four inches depth of drainage will be necessary, and more according to size.
Having drained the pots, the next thing is placing in the soil. When the smallest pots are used for potting cuttings or seedlings enough soil should be placed in the pots, and pressed firmly down, that when the roots of the plant to be potted rest lightly on it the part of the stem which was at the surface of soil before may be fully a quarter of an inch below the rim of the pot. Holding the plant in this position, in the centre of the pot, with the left hand, soil should be placed into the pot with the right, and pressed down firmly and level, the surface of the soil being a quarter of an inch below the rim of the pot. This space is for holding water. When the plants are to be taken out of cutting boxes each should be lifted out carefully with a good ball of earth, and only as much being carefully removed without bruising the roots as will reduce the ball so that it may be easily introduced into the pot intended for it.
When plants are to be shifted the same rule should be observed. Plants do not need shifting unless the soil in the pots is well occupied with roots, and it is considered desirable or necessary to increase the size of the plants. When the plants are turned out of the pots the drainage should be removed, and any unoccupied soil carefully picked off. It should then be placed on the soil (which has been put in the pot and well firmed down previously), and fresh soil packed, either with the fingers, (See page 12.) or a blunt piece of wood, rather firmly. Loose soil holds too much water, and when plants which are potted loosely are turned out there is danger of the ball breaking, and so destroying the roots. When a plant is potted the new soil should always be put in as firm as the old ball is, or when the water is applied it will run through the loose soil and leave the firmer portion, where the roots are, too dry. - London Journal of Horticulture.