Few plants evoke the feel of the Southwest more than Agave and with good reason, Mexico is the center of diversity for this genus and contains about half of the 200–250 species with the rest scattered through the United States, Central America, and the Caribbean. Agaves typically grow on rocky hillsides in exposed, sunny spots but some species will occur in forested areas especially oak woodlands and even occasionally in mixed forests where they will grow on thin rocky or sandy soils. In all cases, the soil drains quickly.
The rosette structure of agaves is particularly suited for arid conditions. The leaves collect water and channel it down toward the base where it can be used most effectively. Contrary to popular belief, agaves do not need dry conditions and in fact thrive in higher rainfall areas provided that they are planted in spots with excellent drainage such as in containers or raised beds, not in Carolina red clay.
Agaves are sometimes confused with aloes and yuccas but are easily distinguishable from both. Yuccas have strappy, leathery leaves which are relatively thin in cross section. Both agaves and aloes have thicker, succulent leaves. Agave leaves have fibers running their length which are used commercially in some species for sisal. Agaves also have a sharp terminal spine and teeth along the leaf margins which are clearly separate tissue from the rest of the leaf. Aloes by contrast have a gooey, gelatinous interior and their marginal teeth are not composed of separate leaf tissue.
Agaves are typically long-lived plants when grown in appropriate conditions. Plants from high elevations are hardy to zone 7 at least while others are strictly subtropical plants suitable for container culture. Most agave are monocarpic meaning they flower once and then die (mono = one, carpic = fruiting). The flower stalks on agave can be separated into two types, one group has a tall spike of flowers often on a slender stalk while the other has a branched inflorescence called a panicle which is often very rigid. After flowering, which in some cases can last two to three months, the main plant dies but usually offsets or pups form around the base of the plant and will take the place of the parent. Usually thousands of seed are also set in capsules after flowering. Despite the common name of century plant agaves in cultivation do not take 100 years to flower.
The JCRA currently has about 60 different types of agave growing on the rooftop and in the Scree Garden and Xeric Garden as well as some other areas of the Arboretum. A plant catching everyone's eye this spring is the Agave scabra in the bed between the Bobby G. Wilder Visitor Center and the Ruby C. McSwain Education Center. The large, waxy coated blue leaves have anchored this bed both in summer and winter for five years now. In that time, it has more than doubled its height and width from 17" to over 36". It originally came to us from the famed Peckerwood Garden in Hempstead, Texas, as seed in 2001.
Agave scabra is a medium-sized agave valued for its architectural form and bluish-green to gray-green leaves which are viciously armed on the margins and tips. It is known as the "rough" agave due to the rough (or scabrous) texture of the undersides of the leaves. The thick flower stalk, invariably described as asparagus-like, has shot to about 15', is branching and will soon be flowering with bright yellow flowers. The species ranges from Texas south through Mexico to the Pacific Ocean and from 500' elevation to 6,500' so provenance of parent plants is most likely important to determine hardiness.
Agave scabra is one of the most ornamental species of agave due to its lovely coloring and large size. It needs full sun and a warm position to thrive and its arching branches are showy in a dry garden or mingled with softer perennials and grasses. Typically it offsets relatively readily although ours has been somewhat stingy in this regard. Come out to visit our flowering specimen over the next couple of months to watch it mature.