Plants with waxy leaves have adapted to excessive sun exposure by reflecting, rather than absorbing radiant heat. Leaf temperatures and evaporation rates are thereby reduced. The waxy surface also limits the amount of water allowed to escape through the leaf pores or stomata. Some plants open leaf pores only at night when the evaporation rate is much lower. Most wax plants grown in the foliage plant industry are cultivars of the Hoya carnosa, a member of the milkweed family, Asclepiadaceae.
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The preferred common name of the species is wax plant, but other names such as wax vine and porcelain flower are sometimes used. A few nurserymen produce species other than the predominant Hoya carnosa. You may also come across Hoya australis, Hoya bella and Hoya multiflora. All of the hoya feature fleshy leaves and flowers covered with a semi-glossy layer of waxy substances known as the cuticle.
Wax plant production is time and labor intensive. The plants require 125 foot-candles or more of light for approximately 10 hours per day. The wax plant is propagated from cuttings harvested from stock vines. It takes three to four weeks for the cuttings to root and four to six weeks more for a single shoot to form on one of the buds on each cutting. Cool temperatures will force the plant into dormancy. A range of 68 to 90 degrees Fahrenheit is optimal for growth.
Soil Conditions and Fertilizer Use
Potting media should feature a high percentage of organic material to provide water-holding capacity. Fibrous peat works well for this. Coarser particles such as pine bark,calcined clay and perlite provide aeration and good drainage. Liquid fertilizer with a 2:1:2 or 3:1:2 ratio is preferred over slow release products, because irrigation frequency lessens as the roots of the plants reach the bottom of the pot, necessitating a drying of the potting medium before subsequent watering.
Production schedules vary widely and are dependent upon cultivar, temperature and degree of water management. Flat-leaf, all green wax plants grow twice as fast as plants with variegated, reflexed leaves. A finished 3-inch pot of wax plant with a 6- to 8-inch long vine takes five to 11 months to grow from an unrooted, single-node cutting. One or two cuttings are typically placed in each 3-inch pot. Four-inch pots accommodate three to four cuttings each.