Yuccas are evergreen, perennial shrubs or trees with tough, sword-shaped leaves and large clusters of white, rounded to bell-shaped flowers. Several species are native to the Southeast and they are described here.
Spanish Bayonet (Yucca aloifolia)
Mature Height/Spread: Spanish bayonet grows slowly to a height of 10 feet. The plant forms irregular, rising stems, one to three per plant. Stems are densely clothed in sharp, pointed, dark green leaves, which are to 2½ feet long and 2 inches wide. White flowers (sometimes tinged purple) appear in summer in dense, erect clusters, which are up to 4 inches across and up to 2 feet tall.
Landscape Use: Spanish bayonet should never be planted near walkways or terraces because of its sharply pointed, dagger-like leaves. The plants are best planted alone or in groups of three, in the background rather than at the front of beds.
Cultivation: In the wild, yuccas grow in full sun on dry soil. They tolerate a wide range of soil conditions as long as the soil is not too wet. Set out potted plants from spring through fall. Little maintenance is required. Remove the flower stalks after blooming. Pollination of most species is done by the pronuba moth. The yucca is entirely dependent on this moth and vice-versa. The seeds are black, flat and look like little wafers. They usually occur in great numbers.
Problems: This is a very hardy, durable plant. Plants are susceptible to leaf-spotting fungi during wet periods. Too much moisture may result in black areas on the leaf margins. Black aphids on flower stalks may ruin the flowers.
Cultivars & Varieties: ‘Variegata’ has dark green leaves marked with yellowish white.
Adam’s Needle (Yucca filamentosa)
Mature Height/Spread: These very hardy plants form a low cluster of stiff, pointed leaves, 2½ feet long and 1 inch wide. The leaves have long, loose fibers at the edges. The stems of the leaves do not rise above ground level. During the growing season, a long stalk will grow up to 6 feet and produce a large number of white, bell-shaped, lightly fragrant flowers.
Landscape Use: See Spanish bayonet.
Cultivation: Provide a sunny location with a well-drained soil.
Problems: See Spanish bayonet.
Cultivars & Varieties: ‘Bright Edge’ has leaves edged in yellow. ‘Colour Guard’ has a broad creamy yellow central stripe, and leaves take on a rose-pink tint in winter. ‘Concava Variegata ‘ has cream-edged leaves tinted pink in cold weather. ‘Garland Gold’ has leaves with a gold center stripe. ‘Ivory Tower’ has out-facing rather than drooping flowers.
Weakleaf Yucca (Yucca flaccida)
Weakleaf yucca resembles Adam’s needle, but has less rigid leaves, straight fibers on the leaf edges and somewhat shorter flower clusters. The leaves are 1 to 1¾ foot long and 1 to 1½ inch wide and bend downwards above the middle.
Cultivars & Varieties: ‘Golden Sword’ has a green margin and yellow center. It is possible that ‘Bright Edge,’ and ‘Colour Guard’, listed above, are members of this species rather than Y. filamentosa.
Spanish Dagger (Yucca gloriosa)
Mature Height/Spread: Spanish dagger is much like Spanish bayonet. This evergreen shrub is generally multi-trunked and grows to a height of 8 to 10 feet. It produces a single, thick, fleshy stem that is crowned with stiff, straight, 1½ to 2 feet long and 2 to 3 inches wide. The leaf points are soft and will not penetrate skin. In late summer, creamy white, 4-inch diameter flowers appear.
Bear Grass (Yucca smalliana)
Mature Height/Spread: Bear grass resembles Adam’s needle, but has narrower, flatter leaves and smaller, individual flowers. Wild plants of bear grass are found in sandy soil around South Carolina and are spectacular when in bloom. The tall spikes of bell-shaped, creamy-white flowers last for two or three weeks and perfume gardens with evening fragrance. The evergreen clumps of soft leaves do not present a hazard like Spanish bayonet.
Curve-Leaf Yucca (Yucca recurvifolia)
Mature Height/Spread: The single, unbranched trunk of curve-leaf yucca grows 6 to 10 feet tall. With age the trunk may branch lightly. The shrub can be cut back to stay single-trunked. It spreads by offsets into large groups. The blue-gray-green leaves are 2 to 3 feet long and 2 inches wide, and they bent down sharply. The leaf tips are spined, but they bend to touch. They are not dangerous. In late spring or early summer large, white flowers appear in loose, open clusters, 3 to 5 feet tall.