This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
At the present day no flowering plant is so generally grown in Great Britain as is the subject of this paper; to give the expression its French meaning, everybody grows it. And it well deserves its popularity, being easy to propagate, easy to grow, will struggle on through much bad management to which it is often subjected, and always abundantly repays those who understand its wants and treat it accordingly. As the writer of the article on this subject in the 'Gardener' for 1870 has treated so ably on the getting up of specimens, we will confine our remarks on it for ordinary greenhouse purposes.
Cuttings can be struck with more or less certainty at any period of the year, though it is only in the case of new varieties that propagation in winter is to be recommended. Excepting where a house is specially constructed for this purpose, no structure is better adapted for it than a Pine-pit, and lacking that a plant-stove. Useful articles for propagating are shallow wooden trays, such as are recommended at page 422 of last volume. These ought to be filled to within half an inch of the top with a compost of sifted leaf-mould and silver sand, the latter preponderating. As a means of reducing the chances of damping off, keep the base of the cutting as near the top of the compost as practicable: if the trays can be placed on the hot-water pipes, roots will be formed all the sooner. A mode of propagating I tried last spring and found most successful, is worthy of extended adoption. It consists simply in cutting leaves which have a prominent bud in their axils out of the stem; it matters little or nothing how small a piece of the stem is attached so long as the bud is there.
They in many cases formed roots quicker than cuttings, and many of them made better plants; but the main recommendation of this system is the greater number of plants that can be obtained by it than by-propagating from ordinary cuttings. I found it best to insert them in a sloping direction, and all sloping one way, as when inserted uprightly they are apt through watering to get tumbled about. Cuttings struck in the spring make nice little plants for autumn and early winter; but summer is the season when they can be struck with least trouble, making serviceable plants the following year. "Well-ripened shoots should be chosen in preference to "sappy " ones, and especially in spring no leaves should be taken off. They may either be inserted in the open ground in pans, round the edges of pots, or singly in small pots. For summer propagation the latter mode is not so suitable as the others, the easiest being the first mentioned. Whichever mode may be followed, they should be potted off, except in the case of those singly in pots, as soon as the roots have grown an inch in length, using 3-inch pots for the smallest ones, and putting them mainly in 4-inch pots.
They make nice blooming plants in this sized pot; and except it be for extraordinary purposes, 7-inch pots will generally be found large enough. The compost I prefer consists of loam, leaf-mould, and sand, the loam of a sound fibrous texture, broken roughly in pieces, using it as four to one of leaf-mould, which should be put through a 1/4-inch sieve, if pieces of wood, etc, are found mixed with it. The Pelargonium enjoys a good quantity of sand, and a sixth part of the compost should consist of it. If the loam should contain much organic matter likely to decompose quickly, less leaf-mould should be added. No manure is recommended, because of the gross growth it engenders; and it is always an easy matter to supply it through the medium of the watering-pot when really necessary. As many crocks for drainage take up room which can be filled with better plant-sustaining material, and there exists no real necessity to use many in the size of pots recommended, more than one crock for 4-inch, and a few more for 7-inch pots need not be used, a little of the roughest of the compost being laid on the crocks. If the plants are properly attended to the roots soon make sufficient drainage for themselves.
Those not intended for winter blooming, should have no more water than necessary to keep the roots in a healthy condition. According to atmospheric conditions, they may require watering from once a-fortnight up to once a-month. When they are watered, give sufficient to moisten the soil in every particle. During this period they may be dismembered of any straggling points; but if cuttings are wanted, this must be deferred till spring. Some time in spring they ought to be shaken entirely free of soil, and repotted in 4-inch, shifting when necessary into 7-inch pots. Treated thus, they obtain a fresh supply of soil every year, keeping them in a state of vigorous health, and reducing the chances of a soured soil to a minimum. It is hardly "worth while growing them longer than three years, as younger plants do as well; a place out of doors may be found for them generally. The Pelargonium appreciates to the full an airy structure. In such, there need be no trouble from disease; but place them in a structure limited in air volume or deficient in ventilation, and they will not thrive. It is simply nonsense to starve them into blooming. When growing, keep them moist at root, and get the pots filled with roots, then there will be no trouble to get them to flower profusely.
I like them to get rather dry after repotting them, using the compost in a medium condition of moisture; afterwards I keep them moist at root. Plants lifted from the flower-garden in autumn, and potted in the smallest pots the roots can be got into, and in the spring shaken out and repotted with the others, make useful plants. There is not probably a better way of getting nice plants of the tricolors and bicolors than by this means; these do well treated the same as zonals. When by any means a plant does become unhealthy, and it is not desirable to consign it to the rubbish-heap, shake the soil from the roots, wash them in soft water, sprinkling sand over them; then pot in the smallest pot practicable, place in a warm medium airy house, and success will be pretty certain. The doubles are stronger growers than the zonals, make more roots, and consequently require more water, but bloom well in the same-sized pots.
There are a few sorts rather difficult to propagate - such are Golden Chain, Avalanche, Lee's Victory, Rollison's Unique, Lady Plymouth, the Pheasant's Foot, more especially the finest cut sort, and probably some others. These ought to be placed in a warm house, in which there is not much water thrown about, and a free circulation of air kept up. With ordinary attention, they strike well in such a place.
If any one should look this over whose space for growing plants is measured by the dimensions of his window-sills, and who has found a difficulty in getting his geraniums to behave " all the year round " as he would like, let him try them in limited pot-room: if well supplied with, water, they will bloom better than if grown in large pots, and winter better also. If wintered in a heated room, they will require water oftener than those in an unheated apartment. They may, after having been dried off, have all the leaves picked off and be stowed away in a cool dry place till spring. I tried some thus last winter, only they were placed in a room devoted to dish-washing and kindred purposes, the water in which used to be frozen in sharp frosty mornings: only one plant succumbed. Fuchsias did not do so well, but a lemon-scented Verbena kept safely. , R. P. B.