CACTI: FOR GREENHOUSE, WINDOW GARDEN AND OUTDOORS
The collective name commonly used to describe the various members of the family Cactaceae is Cacti. These plants are primarily native to the Americas, especially Lower California, Texas, and Mexico south to Chile, Peru, and Argentina, where they grow in the desert and mountainous regions; however, various species, particularly the Opuntia (Prickly Pear), have become naturalized in other countries, including the Mediterranean region, Africa, and Australia, where they were originally planted as hedges but have spread so rapidly that they have become a threat to farmers. In tropical and subtropical countries, Opuntias are planted to form hedges and Opuntia Ficus-Indica produces large edible fruit.
Remarkable Variation in Size and Shape
The members of the Cactus family exhibit great diversity of form; some are small and resemble stones in shape and coloring; others form tall columns 20 ft. in height. The branches and stems of some kinds are flattened, whereas many develop into almost round masses of tissue. A few form true leaves, but in the majority the foliage is reduced to microscopic scales. Some are armed with sharp, pointed spines and all have a very thick outer skin. The absence of leaves and the thick skin enable these plants to flourish in dry, barren climates where most other vegetation can not exist; this because transpiration (giving off water) in Cacti is reduced to a minimum. During the rainy periods Cacti are capable of storing up large quantities of water which is utilized during periods of drought.
In addition to being curiously attractive inform, many Cacti also bear showy flowers of many beautiful shades, and some are night-flowering, as, for example, the large, fragrant, white Selenicereus (Cereus) grandiflorus.
A Vast Family
The Cactus family embraces more than 120 genera, which collectively contain over 2,000 species. The great increase in the number of genera recognized has been brought about by a complete revision of the family by the botanists, who have also grouped the genera into tribes and subtribes, while at the same time dividing many of the old genera into numerous smaller ones.
Thus, of the many Cacti previously named Cereus, only 24 species now remain, the others being split up into no fewer than 38 other genera, the largest of which are Cephalocereus, Pachycereus, Peptocereus, Lemaireocereus, Nyctocereus, Acanthocereus and Borzicactus. Likewise many of the Cacti previously included in the genera Echinocereus, Echinocactus, Echinopsis, Melocactus, Pilocereus, Mammillaria, Epiphyllum, etc., have now been separated into smaller, or transferred to other, genera.
All the important genera Cacti are described separately in this work, but the following notes on their general cultivation will serve as a guide for most of the kinds commonly grown on this continent.
In warm, dry sections of North America, a great variety of Cacti may be successfully cultivated in the open garden. In warm, moist climates fewer kinds succeed but still a selection may be grown, and even in the northern United States a few succeed outdoors in sharply drained (very porous) soils. In such cold climates a location at the base of a south-facing wall is a good place to plant the hardier kinds, one of the easiest of which is the eastern North American native, Opuntia compressa.
Cacti require a minimum greenhouse temperature of 40 degrees and 10 or 15 degrees more is advantageous. With few exceptions, they must be exposed to all available sunlight throughout the year. The exceptions are the epiphytic kinds such as Epiphyllum, Rhipsalis, and Zygocactus. The best potting compost consists of four parts sandy loam, and one part of equal quantities of sand and crushed brick. Repotting is done in April, the plants being moved into larger pots when their roots become cramped. As a general rule, Cacti should be repotted every second year, as after that the soil tends to become sour; but that does not they will of necessity require larger pots.
Good drainage must be provided, about one quarter of the pot space being filled with crocks, covered with coarse leaves, and the soil must be made firm with a potting stick. After repotting, no water is given until the soil becomes almost dry. When the plants are established, the compost is kept moist from April to October. From November until March less water is required, sufficient only to keep the stems from shriveling. When they are grown in window gardens, where winter temperatures are markedly higher than those recommended above for Cacti grown in greenhouses, more frequent watering is needed during the winter months.
How to Take Cuttings of Cacti
Pieces of shoot, or stem, taken from any part of the plants, will form roots. When Cacti produce offsets these form a ready means of increase, for if carefully removed when of reasonable size and potted, they will quickly form roots.
When cuttings are taken they should be laid in the sun for a day or two to allow a corky skin to form over the cuts, which prevents rotting. They are then inserted in pots of ‘equal parts moist peat and sand or in sand alone. The pots are placed on the benches or a shelf in the greenhouse or in a light window. A propagating case is not necessary, although slight bottom heat will induce quicker root formation.
Sowing Seeds of Cacti
Cacti are easily raised from seeds sown in pots of sandy compost in spring or summer, and this method, although slow, ensures the production of really strong, healthy plants. The seeds are just covered with soil, watered and covered with a pane of glass until germination takes place. They germinate best in a temperature of 60 to 70 degrees F. The seedlings should be kept lightly shaded from strong sunlight, and carefully watered until large enough to prick off at an inch apart in pans of porous compost. Later, they are transferred singly to small, 1-in.-wide pots.
This is performed for various reasons. Certain kinds such as Aporocactus (Cereus) flagelliformis and Zygocactus (Epiphyllum) truncatum, being of pendulous growth, are more ornamental when grafted on a tall, erect stem. Pereskia aculeata is a suitable stock for both kinds. Pereskia is grown from cuttings and when large enough, grafting is performed in the following way: a thin slice is removed from each side of the base of the scion; the stem of Pereskia is cut off at the top and a wedge-shaped piece of tissue removed, into which the scion is slipped. The scion is held in place with a pin or large prickle from one of the Cacti. The grafted plants are then placed in a glass-covered box in a warm greenhouse until a union is formed. Cacti which are liable to decay at the lower part of the stem are often grafted on a stock of hardier ty pe and kinds dissimilar in shape are grafted one on the other as curiosities.