Zantedeschia (Calla Lilly)
THE small genus Zantedeschia comprises stemless plants with large, usually arrow-shaped leaves and showy flowers often called calla lilies (though they are not true lilies). Zantedeschias have fleshy rhizomes that run just below the surface of the potting mixture, and from which fleshy feeding roots grow down into the mixture. The inflorescence is a typical arum flower with a central erect spadix surrounded by a showy spathe. It is carried on a long, stout stalk that rises among sometimes above the long leafstalks. In the wild these plants grow in swampy marshland, which tends to dry up during the summer months—a period of dormancy for the plants, when they too dry off and lose their foliage. This pattern must be followed with zantedeschias used as house plants; they can provide only a temporary display indoors during the early part of the year. Dormant rhizomes, however, once given suitable conditions, can be brought into new growth and can flower for many years.
The largest and best known of the so-called calla lilies, has deep green, arrow-shaped leaves up to 18 inches long and 10 inches wide, borne on leafstalks that may reach a length of 3 feet. Flower stalks can appear at any time from late winter to early spring; the inflorescence is a golden yellow spadix surrounded by a milky white spathe 5-10 inches long, which curves slightly outward near the edges. Particularly good as a house plant is 'Childsiana,' which is more compact than the species type and also produces more flowers.
Z. albomaculata (spotted-calla) has dark green leaves marked with silvery white spots; the leaves are narrowly triangular—up to 18 inches long, but only 2-3 inches wide at the base, and are carried on stalks up to 3 feet long. The flowers are more trumpet-shaped than those of Z. aethiopica, with the 4-to 5-inch-long spathe forming a tube; its color varies from white to creamy yellow (or occasionally pink), with a purple stain at the inside base of the tube. The spadix is white. Z. elliottiana (golden calla) has heavily white-spotted dark green leaves, which are broadly arrow-shaped, up to ii inches long and 9 inches wide, with 2-foot-long stalks. The 6-inch-long showy spathe is bright yellow inside and greenish yellow outside, forming an open trumpet around the yellow spadix.
Z. rehmannii (pink calla) has narrow, medium green leaves often spotted with silvery white, that are tapered at each end; they grow up to 12 inches long and 2 inches wide, and have 12-inch stalks. The open-trumpet-shaped spathes are up to 5 inches long; they are usually pink but sometimes are red or purplish. They surround a creamy white spadix.
Many mixed hybrids have been derived from each of the four species that are described above. The flower shapes vary from narrow to open trumpets, and colors include a variety of shades of pink, cream, yellow, and bright red.
Light Provide bright light with some direct sunlight during the months when these plants have foliage. In the dormant period (usually from late spnng to early fall) keep the dried-out plant in a sunny spot in the garden or on an outdoor terrace or balcony—an ideal position as long as there is no risk of frost or very wet weather.
Temperature When zantedeschias are starting into growth (usually from early fall onward), they should be kept cool—if possible, at a temperature of 5°°-55°F—for about three months; thereafter, about 6o° is best for Z. aethiopica, 65° for the other species and the hybrids, until flowering is under way. While they are flowering, keep the plants at normal room temperature; temperatures above 700 are likely to curtail flower life and to make the leaves wither prematurely. For rhizomes that are dormant, temperature is not a consideration.
Watering Water newly potted plants or old rhizomes starting into growth after the dormant period sparingly— just enough to moisten the potting mixture throughout at each watering and allowing the top two-thirds of the mixture to dry out before watering again. As growth develops, increase the quantity gradually until the zantedeschias are in full leaf. Thereafter, water plentifully as often as necessary to keep the potting mixture thoroughly moist; these are among the few plants that need constant moisture at their roots during the active growth period. When in full leaf, in fact, potted zantedeschias can stand in saucers of water. When the plant stops flowering, reduce the amount of water gradually, and stop watering altogether when the leaves become yellow and withered. Leave dried-out zantedeschias in their pots for the entire rest period, whether indoors or out. An occasional brief moistening from rain will not harm the dormant plants, but they must on no account be subjected to prolonged rainfall.
Feeding Once plants are in full leaf, apply standard liquid fertilizer every two weeks, and increase this to a weekly dose when flowers begin to appear, continuing until the end of the flowering season.
Potting and repotting Use a soil-based potting mixture. A single flowering-size plant can be accommodated in a 6-inch pot but larger clumps need either larger pots or small tubs. In the fall, as plants start into growth, move them into pots one size larger, if necessary. When maximum convenient pot size has been reached, divide up plants for propagation (see below). Dry, newly purchased rhizomes can also be planted at this time, either singly in 6-inch pots or three together in an 8- or 9-inch pot. Place the rhizomes horizontally in pots about 2 inches below the surface of the potting mixture.
Propagation Divide rhizomes, or detach offsets that develop around the main rhizome for propagation. Either process is best done at the time of repotting in the fall. Pot single sections of a divided rhizome in 6-inch pots of slightly moistened potting mixture, and treat them as mature plants. Plant small offsets in 3- or 4-inch pots until they are big enough to move into bigger containers, but otherwise give them exactly the same conditions as the larger rhizomes.
It is also possible to increase zanted-eschias from seed. This is the easiest way to get a stock of the mixed hybrids, since they are less readily available as rhizomes than the older forms. Raising these plants from seed, however, is a complicated, lengthy process best carried out in the carefully regulated conditions of a cool greenhouse. It is impracticable for most amateur growers.
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