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.
As summer approaches, the demands of our favourites will be considerable, what with training, potting, and other requisites, this being the period when the bulk of their growth is made. Water must be administered copiously, never once allowing the plants to flag through a deficiency of it.
In my experience I have found great benefit to the plants derived from the practice of inverting small pots over the holes in the bottoms of those intended to put the plants into. These small pots are covered over with broken crocks, then a portion of rough fibry turf, thereby securing perfect drainage. Drained in this way, any amount of water can be given without danger of souring the compost; and it is astonishing to see how fast they form masses of greedy sucking rootlets in this covering of the drainage. This system of draining with small pots is commenced when the plants are of dimensions sufficient to occupy pots 8 inches in diameter.
Should any plant indicate symptoms of stuntedness, lose no time to have the same shaken from its soil, washing the roots by repeated immersions in tepid water; cut back any decayed roots, and repot in lesser pots amongst a compost of equal proportions of silver-sand and well-rotted leaf-mould. Insert the pots in mild bottom-heat, and keep the roots moist; by this change the conditions of such plants will be greatly improved.
No form of training can cope with that of the pyramid-ical; it is imposing in the highest degree, especially when the plants have attained respectable dimensions, with well-clothed sides of foliage. Supposing this form be the aim, the first object is to establish a good foundation by guiding half-a-dozen growths towards the margin of the pots, at equal distances, having selected the most vigorous growth to take an upright direction, to be retained as a leader. Proceed next to secure these shoots in their proper positions by tying each to a light stake, detaching with the lingers only the very extremity of the shoots when they have made four or five joints, according to the habit of the variety.
By this method of stopping, the plants will sustain no check to their progress, but will shortly start out a succession of new wood, which, in its turn, will require to be directed to its proper place, and supported there temporarily by stakes. On no account let there be any scruples about pinching, which must be repeated as often as is necessary to maintain the intended form.
In a cool season no difficulty attends the accomplishment of this; not so in a summer like the one just past. Too strong sunshine has a bleaching tendency, even to the extent of evaporating the colour along with the sap of the leaves, and in numerous instances burning the tissue on the leaves into brown spots. This is especially the case with plants turned out of a warm close atmosphere.
While the slightest shade prevents colouring most effectively both in and out of doors, an open airy situation, on the other hand, produces and accelerates it rapidly. The richest colour I ever witnessed on any tricolor was shown on a plant of Lady Cullum, and this was brought about by the following conditions: After being grown over the summer in a cold pit, open night and day, but shaded from the sun a good portion of the day by a wall which stands opposite, this plant was placed along with others in the full sun, with no other protection than a sash-frame raised above them upon brick piers erected beneath each corner. Meantime the breezes of the most airy situation of the garden were allowed to circulate without restraint.
"While the colouring process is being accomplished, water ought to be afforded them in more limited quantities than previously; but do not allow them to flag for want of it, always supplying the water in the evenings, and syringing overhead at the same time after strong sunshine.
These are gifted with a stronger constitution than the tricolor section, and are thereby more qualified to rough it in winter. With few exceptions the same conditions favourable to the growth of the common zonal will suit them; but, notwithstanding this, where ample accommodation is at command, I should allot them a place by the side of the tricolors, and otherwise treat them the same, with only this difference - viz., add one part more of loam to their compost, and a small portion of guano to their water, while they are finishing their growth.
The following list of sorts we annex; they are all first-rate: Golden tricolors - Lady Cullum, Sir Robert Napier, Mrs Turner, Miss Watson, the Moonston, Jetty Lacey, Sophia Dumaresque, L'Empereur, Queen of Tricolors, and Lucy Grieve.
Silver Tricolors - Italia Unita, Silver Cloud, Glow-worm, Burning Lush, Lass of Gowrie, and Charming Bride.
Bronzes - Crown Prince, Mrs Grimond, Goldfinder, Duke of Edinburgh, Black Knight, Sybil, Prima Donna, Lady Musgrave, Ebor, and Countess of Kellie. A. Kerr.