Although Hoya carnosa (Asclepiadaceae) can be grown outdoors in warm climates, it is commonly grown indoors in hanging containers so that the vines of waxy, dark green leaves can cascade freely. Hoya, native to Australia and Eastern Asia, produces clusters of gorgeous star-shaped blooms every summer, and the blooms get bigger and brighter as the Hoya matures. Start Hoya plants by taking stem cuttings any time of year.
Fill a 6- to 8-inch plastic pot with a mixture of half damp peat moss or perlite and half sand. The easiest way to dampen the potting mixture is to put it in a bucket or large bowl, and add water slowly, stirring until the potting mixture is damp, but not dripping. Set the pot aside while you prepare the cuttings. A 6- to 8-inch container will hold several Hoya stem cuttings.
Cut a 4- to 5-inch tip from the end of a healthy Hoya stem, using a sharp knife or a razor blade. Make the cut just below a leaf, and be sure the plant has at least three or four healthy leaves. Strip the leaves from the cut end of the stem, leaving half to two-thirds of the stem bare.
Dip the cut end of the Hoya stem cutting in rooting hormone. Make a hole in the potting mixture with a pencil or a small stick, and plant the Hoya cutting in the hole with the leaves above the soil.
Put a large zip-lock bag over the pot, and secure it with a rubber band. If necessary, put a few stakes or a piece of bent wire in the pot to keep the plastic bag from touching the leaves.
Place the pot in a warm room, ideally about 75 degrees Fahrenheit. The pot should be in a sunny spot, but not in direct sunlight, as the heat will build up in the bag and scorch the Hoya stem cuttings.
Maintain a humid environment inside the plastic bag. Although the bag will keep the the potting mixture damp for several days, the Hoya cuttings should be checked daily. If the top of the potting mixture is dry to the touch, remove the plastic and mist the potting mixture with a spray bottle.
Dig up a Hoya stem cutting carefully using your fingers or a spoon after two to three weeks. The cuttings should be rooted by this time. When the roots are 1 to 2 inches long, transplant the cuttings into a clean pot filled with commercial potting mixture.
Place the new Hoya plants where they will be exposed to direct sunlight for at least four hours each day. Water the Hoya when the top of the soil feels dry to the touch.