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September Plant of the Month - Purple Hyacinth Bean


Photo of purple hyacinth bean

For an inexpensive but showy climbing vine nothing brightens up the fall garden like the purple seed pods of the purple hyacinth bean (Lablab purpurea formerly Dolichos lablab).

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For an inexpensive but showy climbing vine nothing brightens up the fall garden like the purple seed pods of the purple hyacinth bean (Lablab purpurea formerly Dolichos lablab). The University of Tennessee Gardens has used this annual vine for years for vertical interest, and it never fails to draw questions and admiration.

Purple hyacinth bean is usually sold in seed packs (very economic) and is widely available at garden centers, home improvement centers and mail order catalogs. It is sometimes available as a plant sold in a 3-inch or 4-inch pot. The seeds are very easy to sow directly in the ground or to start in a pot indoors then transplant outside in the spring after the danger of frost has past. Smaller plants seem to transplant better than larger sizes.

This heirloom vine has been grown at Monticello for years and was popular as a standard trellis grower in American gardens for many years. Then, as gardening trends changed, purple hyacinth bean fell out of widespread use. Lately, it has been gaining in popularity again.

Similar in growth habit to scarlet runner beans, the vine produces gorgeous light purple flowers on purple stems in summer. The flowers stay well above the foliage as this showy vine climbs up a supporting structure such as an arbor or trellis. The vine can be a vigorous grower, so the support should be sturdy and at least ten to twelve feet tall as the vine can reach lengths of 15 feet.

As the flowers die, seed begin to be produced in a flat pod, much like a snow pea, that is a brilliant, rich purple color. The seed continue to plump up and the pods to elongate as the season progresses, creating a beautiful display until a frost. The deep purple seed and dark green foliage contrast nicely with fall yellows and oranges. Seed can be harvested and stored for next year’s plants.

Purple hyacinth beans are a food and forage crop in some parts of the world, but CAUTION. They must be properly cooked. Raw beans are poisonous. Typically the plant is enjoyed in the west for its ornamental appeal.

Hyacinth bean can be planted in any well-drained soil in full sun. Only moderate fertilization is required and a fertilizer that is high in phosphorous will promote blooming. Purple hyacinth bean often will reseed if the pods open to drop seed, but they are not an aggressively invasive plant.

Purple hyacinth can be a wonderful selection for the arbor, fence, or trellis for its beautiful flowers, showy seed pods and as an attractant to butterflies and bees. Plan now to use this wonderful vine next year.

 

James Newburn is a research associate in the Department of Plant Sciences at the University of Tennessee. He is also horticulture director for the UT Gardens, which are located in Knoxville on Neyland Drive. The Gardens are a project of the UT AgResearch program. They are open to the public from dawn till dusk. More information is available at http://utgardens.tennessee.edu/.

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Contact:
James Newburn, (865) 329-7256