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A House Plant to Remember

August 10, 1986|BILL DOWNER | Bill Downer has been researching indoor plants for 25 years.

Think of a yam, and what comes to mind is the edible yellowish-brown tuber you find at the grocer's. But that isn't a true yam; it's a variety of the sweet potato, which is related to the morning glory. A true yam is much larger and belongs to an different family of plants, appropriately called the yam family, Dioscoreaceae .

Most yams grow in the tropics, where several are important food sources. Oddly enough, one true yam is a candidate for the indoor garden-- Dioscorea elephantipes , or elephant's-foot. It's also called Hottentot-bread, because it's been cooked by the Hottentots of Africa during famines. A curiosity in the plant world, it's not really a good subject for a beginning gardener. It requires a bright, sunny window, over and around which its vine, supported by a cord or wire, may drape its heart-shaped leaves.

Perhaps the most interesting feature of elephant's-foot is the huge tuber, which can grow to three feet in diameter and looks as though it were carved out of wood. When it's planted, most of the surface remains above the ground, looking like some aged terrapin at rest.

From that tuber the plant's stalk sprouts, winding its way up and about and producing delicate leaves. The contrast between the rough-hewn tuber and the vine, with its delicate, airy appear ance, is dramatic. Flowers, if any, are small, greenish-yellow and not at all showy.

Usually available as a dormant tuber, it ranges three inches to two feet across. Select a pot about four inches bigger in diameter than the tuber. A shallow, bowl-type pot that is deep enough for ample root development is a good choice.

Fill the pot two-thirds full with a potting mix designed for cactus, and add a layer of clean sand. Place the tuber on top of the sand, and work it around until it's solidly in place. Then water liberally, place the pot near a sunny window and don't water again until the mix has dried. This provides just enough moisture to induce root growth and the subsequent sprouting of the vine. Once growth begins, fertilize lightly once a month with any complete fertilizer. Too much water will cause the tuber to rot and destroy the plant, yet waiting until the potting mix is bone dry will cause the leaves to turn brown.

Under less-than-ideal conditions--including the darker, colder months of the year, the vine may become dormant. The leaves and stems will turn brown, and the plant may seem to have died. If this happens, water only when the potting material is completely dry and continue this restricted watering until renewed growth appears; then resume your regular watering schedule. If, however, the leaves remain green and healthy-looking, merely cut back on your watering and feeding schedule to compensate for the decreased light and temperature.

The pest that seems most attracted to Dioscorea is aphids. These greenish insects will appear huddled on the new leaves and shoots of the plant. If allowed to remain, they will damage the growing tip of the vine. You can try washing them off, but chances are that won't help. Your next move is to spray the plant with a diluted solution of Malathion or insecticidal soap. You may need several applications. If you plan to use Malathion, take the plant to a protected area outdoors.

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