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.
This charming plant is not met with in the majority of gardens; and even where it is allowed a place in the stove, it is too often kept for the sake of maintaining a variety. Under such circumstances, its real beauty and usefulness can never be appreciated. That it is well grown in some establishments there can be no doubt, especially where an effort is made to produce flowers for decorative purposes during winter and spring, for which it is invaluable and very effective when well cultivated. Its habit of flowering profusely during winter should alone commend it to growers, without considering the length of time it will continue to produce its flowers in succession, - commencing as it does in November, at the termination of the shoots, and then breaking back and blooming all the way down the stem; in fact, during winter and spring it will continue to grow a little and then produce flowers, keeping the stove gay long after the latest Poinsettias and Euphorbias are over; and on this account the Centropogon should be grown in quantity.
The habit of this plant is somewhat straggling, if an attempt is made to grow specimen plants, or doubtless it would long ago have figured in the front rank at our autumn and spring exhibitions. Nevertheless, it could be grown and trained to look effective for this purpose; but the object of these notes is to describe its cultivation for decoration in small pots.
Its propagation is effected by means of cuttings, which are plentiful during the present month. If taken off much earlier, they are generally flowering shoots, which will do if the object is to get a stock; otherwise they are not recommended, as they do not grow so luxuriantly as young ones which push from the base after flowering. The young shoots root readily if inserted in sandy soil, and placed under the shade of Cucumbers and Melons, or on a shelf if shaded from the sun; and quicker still if placed in the propagating-frame, or under a bell-glass. When rooted, the young plants should be potted singly in 2-inch pots, and grown on in the Melon-house for a time until well established in their pots. They do not grow rapidly at first, as the young shoots inserted as cuttings will not extend many inches in length; but stronger growth will start away from the base, and grow sometimes between 2 and 3 feet in length. When the young plants are established, they should be placed in a pit close to the glass, where more air can be given to them, so that the growth made will be more sturdy and firm.
After they have filled the 2-inch pots with roots, they should be transferred into others 2 inches larger, which should be liberally drained, until they are placed in 5, 6, and 7 inch pots, which are large enough for all ordinary purposes. In potting, care should be taken that the plants never become pot-bound before the operation is carried out, or they will be seriously checked. The drainage only should be removed from the old ball, with as much care as possible, and the soil should be pressed firmly into the pots. After potting, in each case the house or pit should be kept close and moist for a time, until the roots have taken fairly to the new soil. The Centropogon is not particular to soil, and will do fairly well in almost any compost. Rich fibry loam, and a seventh of well-rotted manure, with plenty of coarse sand, and a little charcoal to render the whole porous, suits it well.
While growing, liberal applications of water should be given, and the plants well syringed overhead twice daily. Weak stimulants may be given every alternate watering after the plants have filled their flowering-pots with roots. As the season advances, the plants must be gradually hardened by reducing the artificial heat until it can be dispensed with for a time during the hottest months of the year. The house or pit in which they are growing should be closed early in the day, so as to run up the temperature considerably by sun-heat, as this will prove advantageous to the plants while in cool quarters. As soon as the nights become cold, they should at once be removed where a temperature of 55° to 60° can be maintained. If growth is sturdy, no stakes will be required while growing to support the shoots; but before flowering, short stakes should be placed to each shoot, according to its length, - not too long, as the plants show themselves off to greater advantage when allowed to arch the top part of their growth similar to Euphorbia Jacquiniflora. When grown this way, instead of their whole growth being staked entirely upright, they can be arranged to look more effective amongst stove-plants of a more formal habit.
The flowering shoots stand well out, and thus give to the whole a light and gay appearance. I have found very little advantage to be gained by pinehing the shoots while growing, as this plant has not much inclination to branch into a number of shoots. The strongest shoots only should be stopped. The more moderate growths that throw up from the base should be allowed to extend, as they flower the best, and for the greatest length along the stem. Plants with from one to three good shoots are much better than a greater number of small ones, and look much better when staged amongst other plants.
By propagating two or three sets of plants, a better succession will be maintained, and the latest will be much dwarfer, and therefore better for arranging near the front of stages. This plant has seldom given me much trouble to keep it free of insects. I have never seen anything upon it but a little thrip, which can be easily kept under by liberal syringing. Wm. Bardney.