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 soon as the cutting-pots are rilled with roots, but before the balls become matted, the plants must be shifted into 4-inch pots. Drain the pots efficiently by placing flat pieces of crocks on the holes in their bottoms, over which put an inch in depth of half-inch bones and wood-charcoal. Next to this the rough portions of the compost, to a depth that when the balls are set on it the plants will stand no deeper in the new pots than what they did in the cutting-pots.
These rules in reference to drainage and keeping the plants a little higher in the fresh pots must be attended to at each succeeding shift. Some varieties amongst the fancies are at times subject to canker, or rot off at the surface of .the soil. As a preventive to this, they should stand a little higher in the new pots than they did in the old, giving the soil a gentle slope from their stems to the sides of the pots, which will prevent a superabundance of moisture at a point where it is likely to be injurious.
All being ready, turn the plants out of the pots, and, without disturbing the balls, remove a little of the old drainage. Place them in the pots prepared for them, and with a flat piece of wood make the fresh soil firm around the balls. This completes their first shift, and to prevent repetition, all future shifts are performed in a similar way. If the soil is in a proper condition as regards moisture, the plants will not require water for two or three days after being repotted. It is a bad plan to saturate newly-potted Pelargoniums. Their roots will take much quicker to moderately dry soil.
Continue the plants for a week or so in the propagating structure, then remove them to the greenhouse, placing them in a position as near the glass as practicable. After they have been here a few days, cut them back to four eyes from the surface of the soil. In most cases each eye will put forth a shoot, which, on attaining sufficient length, must be pegged down to the soil with hooked pegs for the purpose. In doing this, be careful not to break the shoots; they are liable to snap off at their junction with the main stem. It is therefore best to go over them several times, bending them down a little on each occasion until the desired position is attained.
About the first week in June they will require another shift, the large-flowering kinds into 8-inch and the fancies into 6-inch pots. A cold frame standing in an open position, clear of trees or anything that would prevent the plants receiving the full benefit of sunshine, will be the best place for them from now to the end of August.
To prevent worms entering the pots, stand them on inverted pots of similar dimensions.
As soon as they have started growing in the fresh soil, the large-flowering varieties must have their shoots cut back to within three buds of where they start from the main stem. These buds will nearly all send forth shoots, which must be kept neatly tied to small stakes, training the outside shoots as low as possible, keeping each clear of its fellow.
The fancies will not require cutting back at this time. In general they make a sufficient number of shoots to form the plants without undergoing this operation at present. Train their shoots as directed for the large-flowering kinds, and nip off all flower-buds as they appear. To induce well-matured growth, give abundance of air day and night. On fine days remove the sashes altogether, putting them over the plants again at night. By the first week of August the plants will require another shift. Give the large-flowered sorts pots 10 inches in diameter, and the fancies 8 inches in diameter. About the middle of the month the large-flowered kinds must have their shoots cut back to within two eyes of where they started from when cut back in June. The fancies should have their shoots shortened sufficiently to give symmetry to the plants, but they will not require cutting so hard back as in the case of the large-flowering kinds.
After being cut back the plants will require little water until they have put forth fresh shoots. The first week of September they must be taken back to the greenhouse. Give them a place near to the glass, each plant standing clear of its neighbour. The fancies should have the warmest end of the house, and they should not be exposed to currents of cold air during the winter. If their shoots become crowded, thin them to the desired number, remembering that a less number of stubby well-matured shoots will produce a better result than a greater number not properly developed.
If intended for exhibition in June, the plants must be got into their blooming-pots not later than the first week of January: 12-inch pots will do for the large-flowering kinds and 10-inch pots for the fancies. The shoots will require their tops taken out at the same time, remembering to operate on all of them.
If not wanted to bloom until July, the second week of February will be time enough to repot them and nip out the points of their shoots. As the shoots lengthen, keep them neatly tied to stakes, bending the outside ones down close to the rims of the pots, so that, when in flower, the plants will present in shape half a ball equally flowered on all sides. "When the plants commence flowering they must be shaded from sunshine which will improve the look of the flowers, and cause them to continue longer in bloom than if shading was omitted. As soon as the blooming season is over, the plants must be set out of doors in the full sunshine. Remove some of the largest leaves, and gradually reduce the moisture at their roots. This will cause the wood to ripen previous to their being cut down, which should be done not later than the second week of August. After being cut back the plants should be set in a cold frame, where they can be protected from rain, as they must have no water until the eyes have started afresh. As soon as it is seen that they have done so, the plants must be turned out of the pots and the balls reduced to about one-half their present size, so that they may be got into as small pots as possible, using the same kind of compost as before.
Their future treatment must be the same as described for young plants.
In conclusion, I recommend the grower of Pelargoniums to observe the following hints. Never water them until they really require it, and then give sufficient to thoroughly moisten the mass of soil in the balls. Keep them at all times free from green-fly. Fumigate them just before the first flowers open, whether you can see any appearance of green-fly or not. Keep them as near the glass at all times as you possibly can. Wet their foliage as seldom as possible. When the blooming pots become filled with roots, set them inside of others a size larger: this will prevent the roots from getting injured through the sun or dry air acting on the outsides of the pots in which the plants are growing. As soon as the flower-buds appear, assist the plants with manure-water at every second watering. Let the water be of the same temperature as the house in which the plants are growing. J. H.