This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
(Greek, double gland, referring to the two glands at base of ovary, which distinguish this genus from Echites). Apocynaceae. A charming genus of greenhouse twiners (sometimes erect), mostly from Brazil.
Flowers large, showy, more or less funnel-shaped, having a remarkable range of color, rarely white or dark red, but especially rich in rosy shades and with throats often brilliantly colored with yellow; the buds, also, are charming; calyx 5-parted, the lobes lanceolate, with glands or scales in the inside; corolla without scales at the throat, the 5 lobes spreading, twisted in the bud; stamens 5, affixed in the top of the tube, included, the acuminate anthers connivent around the 5-lobed stigma; disk of 2 fleshy scales, alternating with the 2 distinct ovaries: fruit of 2 terete more or less spread-ing follicles. - Species 30-40, in tropical S. Amer., woody (rarely herbaceous) and mostly at first erect but becoming scandent, the leaves mostly opposite and entire and usually with bristles or glands at base; flowers usually in terminal or axillary ra-cemes. The genus is fully as interesting as Allamanda, which belongs to another tribe of the same family. Other allied genera of garden interest are Echites, Odontadenia, Mandevilla and Urechites. Some species are naturally erect bushes, at least when young, and many can be trained to the bush form. The group is a most tempting one to the hybridizer. Many names appear in European catalogues, but they are confused.
Very many pictures are found in the European horticultural periodicals.
Fig. 1274. Dipladenia atropurpurea. (X 1/5)
Of the twining glasshouse flowering subjects, dipladenias are amongst the best and ought to be in all collections of greenhouse plants. An erroneous idea is held by many that it is necessary to have a very high temperature to grow these plants successfully. This, however, is not the case. Except when started into active growth in the early spring, they do better in an intermediate temperature. Dipladenias have been known to live, and thrive well, after having been subjected to 7° of frost. A good time of the year to secure cuttings of dipladenias is about February 1. At that time they show signs of starting into growth and the weak wood should all be pruned back to the normal thickness of the stem. The thickest part of these prun-ings make good cuttings. Take a piece with two leaves attached, with about an inch of the stem under the leaves. Pot them singly in small pots, half filled with equal parts osmundine, broken up rather fine, sand, and charcoal. Fill the upper part of the pot with sand. Place the pots in a tight propagating bed, in a night-temperature of 70.° Allow,the temperature to run up to 80° or more by day, but be sure and admit air several times during the day by opening up the case the plants are in for a few minutes.
The cuttings will have the small pots filled with roots in about a month, when they may be shifted into larger pots. From now on, use for potting equal parts of osmundine, the fiber of loam out of which all the fine part has been shaken, sphagnum moss, sand and charcoal. When the plants reach a 6-inch pot, a sixth part of sheep-manure may be added and a sprinkling of chicken-bone. It is a good plan, provided one has a good sheltered border with a southern aspect, to plant small plants of dipladenia outdoors from June until the middle of September. It is astonishing how vigorously they start into growth and flower when potted after this treatment. Fifty-five degrees is a good night temperature to grow dipladenias in when possible. During the summer, if grown indoors, admit all the air that can be admitted day and night. They will stand the full sun under glass, but they do slightly better under a very light shade during the hotter part of the day, when the sun is shining. When the pots are filled with roots, and it is desired that they should remain in that pot for the rest of the season, feed with manure-water, a handful of cow-manure to a two-and-a-half-gallon watering-pot. The same amount to an equal quantity of water if a fertilizer such as "Clays" is used, is sufficient.
Horse urine may also be used for a change, a 3-inch potful to two and one-half gallons of water. Be sure to water three times in between with clean water. Dipladenias show signs of completing their growth toward the end of November, at which time water should be gradually withheld, but never so as to allow the wood to shrivel. They may be treated in this manner until the end of January, when, as stated above, they will show signs of starting the season's growth. At this season they should have a general overhauling. Large plants should be turned out of their pots, and the loose dirt all washed out of them with a hose with a gentle pressure on it; and if possible repot in the same size of pot. After disturbing the roots in this manner, they are better to be placed for a few weeks in a temperature of not less than 65.° When they have gripped the new soil, they do better in 55° night temperature. Give each break a piece of thread attached from the plant to the roof to climb on until they set flower. A few breaks, near the highest part of the plant, will start climbing ahead of the others, and after they show a flower-stem pinch the shoot immediately ahead of the flower. This will encourage the belated breaks to start and catch up to these leaders.
When they have all set flower, they may be trained evenly over a globe trellis if they are desired for a specimen plant. By the above treatment ninety-five open flowers, all at one time, have been secured on a plant in a 12-inch pot. Dipladenias are subject to mealy-bug, scale, thrips, and red-spider. Fumigate with hydrocyanic gas during the cold months, and syringe regularly and thoroughly during the summer, and these pests will give no trouble. (George F. Stewart.)