White moonflower (Ipomoea alba) and purple moonflower (Ipomoea turbinate) are sprawling, many-blossomed vines that bloom at night and are noted for their fragrant blooms. Although lovely, however, these large, twining plants can easily become invasive in most parts of the United States.
White moonflower is a tender perennial vine winter hardy to U.S. Department of Agriculture plant hardiness zones 10 through 12. Native to tropical America, it is not as prolific or hardy as its cousin the purple moonflower, more commonly known as purple morning glory, which is likely native to India and is almost never grown as an ornamental. In many areas of the United States, both white and purple moonflowers have been reported as invasive species that have escaped and naturalized. Both are night-blooming flowers with strong, pleasant fragrances.
Size in the Wild
Both moonflowers grow rapidly once established. White moonflower in its native habitat may grow as tall as 70 feet, twining into jungle trees and natural climbing structures. Purple moonflower has similar vining tendencies, but as a weed it is often eradicated before it can reach full size. Blossoms of the white moonflower are about 4 inches across, while purple moonflower blossoms are usually significantly smaller, about 2 inches wide.
Size in Cultivation
Only white moonflower is typically cultivated. In the home garden, it usually doesn’t achieve a height and spread of more than 10 to 15 feet. It oftentimes won’t even get this large, unless given considerable support -- as with a trellis or fence -- and allowed to sprawl on the ground. Especially considering how tender it is, it dies in most American gardens before it can grow any larger. However, within its hardiness range, it may grow larger. In most parts of the United States, purple moonflower is no longer sold as an ornamental.
Moonflowers, both cultivated and wild, prefer well-disturbed soil, full sun and medium moisture. In the garden setting, white moonflower grows well in well-drained areas. In the wild, moonflowers -- especially purple -- tend to invade prepared planting sites such as crop fields. When growing moonflower, try to contain it by growing close to the house and keeping an eye on it. Once it escapes its planting area, it is difficult to control.