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.
(Latin calceolus, a slipper, alluding to the saccate flower; these plants are sometimes called lady-slippers, but the name is best used for Cypri-pedium). Scrophulariaceae. Showy-flowered herbs and shrubs, grown both in the greenhouse and in the open.
Leaves mostly opposite, usually hairy and rugose, entire or incised or pinnatifid: corolla 2-parted nearly to the base, the lower part or lip deflexed and inflated slipper-like, the upper lip smaller and ascending, but usually saccate; stamens 2 or rarely 3, and no rudiments (A, Fig. 739): fruit a many-seeded caps. - About 200 species, mostly from the Andes of Peru and Chile, but extending north to Mex.; also 2 in New Zealand. Monogr. by Kranzlin, Engler's Pflanzenreich, hft. 28 (1907).
Many species of Calceolaria have been cultivated at one time or another, but the number now grown is few, most of the garden kinds apparently being hybrids or marked variations from specific types. The genus falls into two horticultural sections, the herbaceous kinds, and the shrubby kinds. The former are the only ones generally known in this country, being treated more or less as annuals. The herbaceous garden forms Rodigas considers to be offshoots chiefly of C. arachnoidea and C. crenatiflora, and he has called this race C. arachnoideo-crenatiflora (see I.H. 31:528,536; 35:54). In this work, however, the more inclusive terms C. herbeohybrida of Voss is employed (Fig. 739); and also the corresponding C. fruticoybrida for the shrubby derivatives. C. crenatiflora seems to have left its impress most distinctly on the greenhouse forms. The calceolarias are grown for the variously colored and often spotted slipper-like flowers. The shrubby forms, grown much in England, do not thrive in the heat of the American summer.
The cultivation of the herbaceous and the shrubby kinds of calceolarias is about the same, with the difference that the herbaceous kinds are nearly always grown from seeds, while the shrubby varieties are oftener grown from cuttings. - Seeds may be sown from the end of March until the first of September, according to the size of the plant required. Those sown early are more easily carried through the hot months than any that are propagated in the end of May or in the month of June. Sow the seeds in shallow pans with good drainage in a compost of equal parts of sand and of the peat which is shaken out of fern-root that is to be used for potting orchids, adding about one-fourth of charcoal. All this should be sifted through a fine sieve. This material should be well mixed and placed an inch in depth in the receptacle that the seeds are to be sown in. The surface should be made as level as possible, and the seeds, after being thinly scattered over the same, may be pressed gently into the compost, covering them very lightly with sphagnum moss sifted through a very fine sieve. Water by dipping the pan in a tank of water, allowing it to soak through the holes in the bottom of the pan.
This mode of watering is not so liable to disturb the small seeds, as an overhead watering with a fine rose on the watering-pot. A temperature of 60° will cause calceolaria seeds to germinate, but the sun should not strike them until the cool of autumn comes. A greenhouse with a northern aspect is best for them until the end of September, giving all the air possible day and night. From the first of October until the end of March, the plants will stand the full sun, and should then be grown in a night temperature of 40°, allowing 10° or 15° of rise during the day. For a first potting (which may be to 2-inch pots) the same mixture in which the seeds were sown is the best, and the seedlings should be big enough to be easily held between the finger and thumb; and as the plants are moved along into larger pots, equal parts of fibrous loam, fern-root, leaf-mold, sand and dried cow-manure may be used, always having this compost in as lumpy a state as can be equally and conveniently packed around the plant. When the plants are well rooted in their flowering pots, they may be watered with manure water.
An ordinary handful of green cow-manure to about three gallons of water may be used, and if any of the commonly used fertilizers are to be employed for a change, the same amount of fertilizer to an equal amount of water is about right; but always water with clean water twice between these applications. - If cuttings are to be used for the propagation of calceolarias, they should be rooted in a temperature of 45° to 50°, kept shaded from the sun. Cuttings may be procured from the plants that are trimmed into shape during their growing period (in August or September) and should have two leaves attached and another joint to go in the sand. When rooted, treat them as described above for the seedlings. The varieties of the rugosa section are largely used for bedding plants in Europe. - Calceolarias are very subject to attacks of green- and white-fly; the best means of keeping these pests in check is by fumigation with hydrocyanic gas. In the evening is the best time to fumigate, and the foliage of the plants should be perfectly dry; in fact, it is better if possible to use no water at all in the greenhouse the day they are to be treated.