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.
I have already stated that Roses love a rich diet when in a healthy growing state. A little weak guano-water will stimulate a healthy development of foliage, and as the wood makes growth, it can be exchanged for some dry cow-dung placed on the surface of the pots, and the water poured over it. Water, into which has been placed a small portion of soot, is a good thing to give the plants, and with this administered copiously, and air admitted plentifully, even in damp days, rather than being content with a close atmosphere, which creates mildew, and predisposes the plants to be affected by green-fly, the Roses can scarcely help flourishing well.
Hard forcing should be avoided, as being detrimental to the production of well-finished blooms. Should occasion arise for some flowers being urgently required, select those plants whose buds are well swollen, plunge them into a bottom-heat of some 70° or 80°, with a temperature of about 60°, and with air freely admitted during the day. Allow the plants to continue there until the most forward buds begin to expand, when they can be removed to a genial and sunny position in a warm conservatory: here the process of expanding can be completed, and the plants will retain their flowers much longer than if permitted to unfold them in the forcing-house.
It is of small importance what kind of structure the plants are grown in, if the conditions under which they flourish best are supplied. These conditions are, a sunny exposure near the glass, in a light and airy position, in a temperature ranging from 40° to 60° when the sun shines. A higher temperature is likely to prove injurious, as the growth becomes weakly, drawn, and colourless. From 36° to 38° will not be so injurious as over 60° at this period of the year. If the cultivator could command the sunshine and cool soft air of September all the year round, he would have exactly the condition of atmosphere best adapted for the growth of Tricolor and Bronze Pelargoniums. Let it be understood that all cold draughts of air should be excluded - i.e., they should not be allowed to play directly on the plants.
All leaves should be removed as they decay; it is best to detach the leaf at the point where it joins the stem, leaving that to drop of its own accord. This prevents any damage to the stalk by displacing the leaf-stems while they are yet green. The plants should be turned about at intervals to secure uniformity of growth. As soon as the cutting-stem is 4 inches in height, remove, by using the point of a knife, the two uppermost leaves and shoot while yet undeveloped; this will check the upward growth, and cause side shoots to appear, which should be pinched back in their turn to secure a nice bushy-habit. This course of treatment will lay the foundation of well-grown and symmetrical plants. Continue thus to train and turn about the plants, and remove dying leaves; repot when the roots reach the sides of the ball as before, using pots two sizes larger to succeed those the plants have occupied.
By this time the winter will have passed away, and the plants be growing apace. A vinery just started will now be an excellent place in which to stage the plants, near the front ventilation. The temperature which best suits the vines at this stage will be that best adapted for the Pelargoniums, so long as it does not rise much above 60°. But when it becomes necessary to raise the temperature of the vinery above that point, the plants had better be returned to their old quarters.
At the time of the next shift, if the plants are in vigorous condition, a little bone-meal (not bone-dust or broken bones, but a fine bone-flour) may be added to the heap of soil in the proportion of about one-tenth. This will stimulate the plants to make considerable growth, and is to be preferred to manure water.
Up to the time that the leaves begin to colour, pure water should be given; then, when the leaf-coloration is required, some weak cow-dung water may be given, with a small portion of soot added to it: the last-named material greatly helps the development of colour.