This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
The application, or, rather, the misapplication of water, kills more pot plants than anything else. It is also a subject that will not admit of definite rules, so much depends upon individual circumstances. When a plant is wet, it of course requires no water, yet many water all their plants every day. When a plant is dry, sufficient water should be given to reach every root, and wet all the soil; yet many are content by dribbling a little, on the surface. Strong growing plants, and those that have filled their pots with roots, will require more water than those under the opposite extremes. Plants maturing their growth, or coming towards a state of rest, should have a gradually diminished supply, not, however, by curtailing the quantity at each application, but by lengthening the period between them. Merely wetting the surface only deceives the eye, as the lower roots get none. Again, delicate rooting plants, as azaleas, heaths, epacris, lesohenaultias, etc, especially if recently repotted, will frequently appear dry on the surface, although not in need of water.
To ascertain accurately, give the side of the pot a sharp rap; if it produces a clear, ringing sound, it is a sure sign that there is not much moisture within.
Calceolarias and cinnerarias are difficult to keep over summer. The best method is to plant them deep, in a rich, open soil, clear away a few of the lower leaves, and draw the soil well up about the stems; unless they emit a fresh supply of roots, and get hold of the soil before summer, they will do but poorly.
Pelargoniums will soon be in perfection. Keep them regularly supplied with water, and cut off the faded blooms. They will keep in flower for some weeks, if regularly attended to in these particulars.