Some perennials are too easy to grow. Curve leaf yucca, Yucca recurvifolia (or Yucca gloriosa ‘Tristis’), is remarkably resilient. It migrates slowly but surely. If it becomes obtrusive, it is difficult to contain and remove. Removal of foliar rosettes above does nothing to slow the roots below. The roots merely produce new foliage. Of course that can be a distinct advantage for harsh conditions.
The striking foliar form resembles that of other species of Yucca, except that it reliably arches softly downward. Foliage is not as soft as it seems though. Each leaf terminates with a sharp spine. Sharp edges can cause wicked paper cuts. Foliar color is bluish gray. Although, variegated cultivars are increasingly popular. Old plants can develop trunks that slowly grow more than six feet tall.
Tall and elegant spikes of relatively small creamy white flowers stand grandly above the evergreen foliage in late spring or summer. Bloom is best with warm and sunny exposure, and lasts a long time. Viable seed is rare. Propagation by division of some of the many pups is simple though. Popular variegated cultivars exhibit more docile growth with fewer pups, but bloom less abundantly.
From a simple picture, Spanish bayonet, Yucca aloifolia, is indistinguishable from the common giant yucca. The narrow leaves are about two feet long, and flare upward and outward from terminal buds. Plump conical trusses of waxy white flowers with purplish highlights stand vertically just above the foliage. The main difference is that the leaves are more rigid than they appear to be, with nastily sharp terminal spines.
The second most obvious difference becomes apparent as the trunks mature. These trunks get only about four inches wide, which is not quite stout enough to support their own weight. Some might get taller than ten feet, but eventually fall over. Terminal buds of fallen trunks curve upward, and try to grow vertically again. If not pruned away, old foliage browns and lays back against the trunks, like the beards of fan palms.
Yuccas are almost as useful as aloes are for gardening in chaparral or desert climates. I say ‘almost’ because most are not quite as friendly. The leaves are outfitted with nastily sharp tips. It is how they protect themselves from grazing animals in the wild, but it is not such an advantage in home gardens. Some actually have the potential to be dangerous where someone could bump into them. The leaves of Joshua tree can puncture leather. Some types of yucca get so big that they make it difficult to avoid their nasty leaves, even if planted in the background.
That being said, for those of us who do not need to worry about endangering children, dogs or anyone else out in our gardens, yuccas are very distinctive and handsome plants. Their striking foliage radiates outward from dense foliar rosettes. Large spikes of creamy white flowers that bloom in summer or autumn stand above the foliage quite boldly. Some yuccas produce remarkably tall floral spikes. Our Lord’s Candle, Yucca whipplei (Hesperoyucca whipplei), is a terrestrial yucca that sits low to the ground, but produces a huge flower stalk that stands ten feet tall! Modern garden varieties of Adam’s needle, Yucca filamentosa, are variegated.
Of the yuccas that develop sculptural trunks, only a few are available in nurseries. The giant yucca, Yucca elephantipes, is almost too common in mild climates, and unfortunately develops a massively distended trunk that is too big for some of the situations it gets into. Most other trunk forming yuccas that grow slower are uncommon because they are susceptible to rot in landscapes where they get watered through summer.
Except for a few tropical yuccas that are very rare, yuccas are very drought tolerant. Even in desert climates, some yuccas survive on annual rainfall. Others are happier if watered a few times through summer. Giant yucca happens to be a tropical yucca, but surprisingly does not need much water.
Giant yucca is very easy to propagate from cuttings of the big canes. Even big pieces can be cut and stuck as cuttings. However, most of the tree yuccas are difficult to propagate.
Terrestrial yuccas that do not develop trunks are generally easy to propagate by division of pups, although some are difficult to handle. Some terrestrial yuccas actually develop small trunks that creep along the ground, or maybe stand a few feet tall. They can be propagated as cuttings like giant yucca.