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Agave and Yucca: Tough Plants for Tough Times¹

Many people rightly think of agave and yucca as tough plants associated with extreme climates like deserts and dunes. What they may not realize is that agave (Agave spp.) and yucca (Yucca spp.) also adapt well to home and commercial landscapes, where they thrive in the sometimes harsh conditions associated with urban environments.

Interest in agave and yucca has grown recently, thanks in part to increasing water restrictions in many Florida urban areas. Agave and yucca are found in native environments that typically are dry, hot, sunny, and windy with low rainfall and poor soil. In cultivation, this adaptability translates into low maintenance since typically they need little or no irrigation, fertilizer, pruning, or spraying. Furthermore, many agave and yucca withstand drought, heat, strong winds, and cold weather, and have few pests and diseases. They are tolerant of poor soils and therefore rarely develop nutrient deficiencies. The wide variety of sizes, shapes, and growth characteristics permits many landscape uses, including groundcover, bedding plants, container plants, shrubs, and, especially, dramatic specimen plants. Table 1 lists a number of species and cultivars available, along with their descriptions.

Above and beyond their toughness, agave and yucca capture the imagination because of their dramatic architectural forms and unusual shapes. In addition, these plants boast intriguing defensive "weaponry"—stiff, hard, or leathery leaves, often armed with barbs, teeth, or spines. Because of this armor, many of these plants can present a hazard, especially to small children.

Agave

Agave tends to have more armor than yucca. Each agave plant consists of a rosette of long, stiff, spear-shaped, fleshy leaves often armed with teeth and tipped with a long terminal spine. Agave spp. are familiar to most people thanks to the commonly grown century plant, Agave americana, but there are more than 200 additional species of agave with potential landscape use.

Agave varies in size from a few inches to more than 12 ft. tall and wide. Leaf color ranges from deep green to grass green to blue green to gray, and leaves may be striped or mottled with white, cream, yellow, or chartreuse. Though it sometimes takes years for flowering to occur, agave develops branched spikes of yellow, rose, or white tubular flowers on incredibly tall stems 6–40 ft. above the plant. After flowering, the parent plant typically dies, although usually a number of small plants form around the base of the parent plant. The small plants are technically called "offsets" but are commonly called "pups." These may be separated from the parent plant for propagation. Two species of agave are native to Florida: false sisal (Agave decipiens) and wild century plant (Agave neglecta).

Yucca

Yucca is similar to agave but often forms trunks and typically has more numerous, thinner, leathery leaves with a smaller terminal spine. Yucca leaves range in color from deep green to pale blue, and leaves may be striped in shades of white, cream, yellow, or chartreuse. When in flower, yucca produces large, upright panicles (flower clusters) of white, bell-shaped flowers. Unlike the tall flower stems of agave, yucca flower panicles are held within or just above the foliage. There are more than 20 species of yucca, of which three (or four) can be considered native to Florida: Spanish bayonet (Yucca aloifolia), Adam's needle (Yucca filamentosa), and moundlily yucca (Yucca gloriosa). Florida taxonomists believe curve-leaf yucca, Yucca recurvifolia, is the same as moundlily yucca (Y. gloriosa), whereas Agavaceae taxonomists consider Y. recurvifolia a separate species.

Plant Requirements and Placement

Almost all agave and yucca selections require full sun (at least six hours of direct sunlight) for best appearance and growth. Much of Florida has sandy, well-drained soils on which agave and yucca can thrive despite the rain and humidity. However, even with sandy soils, some desert agaves are difficult to grow in Florida.

Areas with perched water tables or heavy soils can still grow agave and yucca, provided these plants are grown above grade or on a slight mound that provides better drainage. Another alternative is to amend the soil to improve drainage. A final option is to grow these plants in containers with well-drained potting soil and irrigate as needed.

Winter soil drainage is especially critical in northern Florida. Roots often begin to rot during cool, damp winter weather if growing in conditions with poor drainage.

Table 1 lists agave and yucca in the collection at the North Florida Research and Education Center in Quincy. The table also indicates cold damage (if the plant was located outdoors) based on observations after successive low temperatures during the winters of 2009–2010 and 2008–2009. Low temperatures include 21.50°F on January 22, 2009, and 28.44°F, 22.13°F, and 15.26°F on December 21, 2009, and January 5 and 11, 2010, respectively.

Water and Fertilizer

Agave and yucca require occasional watering after planting to aid with establishment. Thereafter, most agave and yucca plants will thrive on rainfall alone.

Similarly, most established agave and yucca do not need fertilizer and will subsist in many urban soils, especially if organic mulch is used. Low rates of fertilizer may be applied to young or small plants to aid establishment or improve growth rates.

Pests, Diseases, and Cultural Problems

The most serious pest is agave snout weevil (Scyphophorus acupunctatus). The adult female weevil, about 1/2 in. long and brownish, uses its "snout" to puncture the base of a plant and lay eggs. In this process, microorganisms are introduced that decompose plant tissue, usually causing the plant to wilt, collapse, and die. White, grublike larvae develop from the eggs and feed on the decaying tissue. The grubs (which are, incidentally, the "worm" traditionally placed in some bottles of tequila) eventually pupate and emerge as adults, with the entire life cycle lasting 60–90 days. This weevil can attack all species of agave, though large-growing species with broad leaves (like century plant, Agave americana) appear more susceptible than small species with hard or fibrous leaves. Weak plants or agave plants that are about to flower are especially vulnerable. Yucca spp. are occasionally attacked. Control of agave snout weevil is difficult, and infestations can be prevented by maintaining healthy plants and destroying infested plants.

Plant bugs (Caulotops and other species) are small insects that occasionally build up in large numbers and damage agave plants by feeding on leaves, resulting in light yellow scars or spots. Yucca plant bug (Halticotoma valida) causes similar damage to Yucca spp. Plants weakened by too little light or too much water may become infested by various mealybugs or scale species. Eriophyid mites occasionally feed within vegetative buds of container-grown plants, resulting in leaf scarring or abnormal growth. Most disease problems are various root rots usually associated with wet soils and often exacerbated by cool temperatures and weakened plants.

Agave and yucca are native to cool, temperate areas, high-altitude areas, and tropical climates. However, their broad and often fleshy leaves and stems make them susceptible to freeze damage, particularly when grown outside their native range in cold or humid climates or irrigated areas. Freeze damage occurs when these species are exposed to temperatures below their range of adaptability for several hours. A few days after the freeze, spots, cracks, or areas appearing water soaked will develop on damaged leaves; severely damaged leaves will appear mushy. These areas will eventually dry and turn brown, making the leaves unsightly. Unfortunately, removal of damaged leaves often alters the canopy or symmetry of the plant, resulting in an unsightly specimen. Although severe freeze damage may kill the plant, freeze damage often stimulates offsets on lower portions of the plant.

Container Gardening

Agaves and yuccas are excellent plants for containers. Their coarse, bold textures and odd shapes add interest, making them excellent specimen plants and focal points. Agave and yucca are particularly well suited for containers because their low water requirements and drought tolerance permit longer intervals between watering than most other plants. Finally, growing agave and yucca in containers allows for use of well-drained potting soils and flexibility in relocating container plants to sheltered areas during extreme rain events or cold weather. Containers may provide the only way to successfully grow arid, desert-adapted species in Florida's humid climate.

Propagation

Many species of agave and yucca spontaneously form new plants from offsets or "pups." Technically, these are new shoots that develop from underground rhizomes. Offsets can be removed from the original plant at any time, although well-rooted and larger offsets result in faster establishment and growth. Some Yucca spp. additionally form suckers at the bases of stems. These may be similarly divided, dug, and planted. Development of offsets often is stimulated by plant damage or stress.

Bulbils, which are small plants attached at the base of the flowers, may be used to propagate some species of agave. Bulbils usually develop as the flowers die. They can be removed and potted at any time, but they establish faster if allowed to remain on the flower stalk until at least four leaves have formed.

Yucca may be rooted from rhizome or stem cuttings. Three-inch sections of rhizomes can be collected in late winter and placed horizontally on well-drained potting soil in a warm, humid environment; shoots and roots form several weeks later. Semihardwood cuttings from the current season's growth also may be collected and rooted similar to other woody plants, although greater success usually occurs with Yucca spp. native to humid environments.

Agave also may be propagated by cuttings, but, in this case, leaf cuttings are used. Mature leaves are cut and the cut portion of the leaf is allowed to callous. They are then placed cut-side down in a well-drained rooting substrate. Under commercial nursery conditions, small plants form along the cut base of the leaf after several months.

Seed of agave and yucca may be harvested from mature capsules and sown fresh or stored for up to five years. Germination usually occurs within three weeks of sowing. Seedling growth rate varies with species.

Historical and Modern Uses

Almost all species of agave and yucca have been used by the native peoples of the Americas for food, fiber, fencing, or soap. The most well-known usage of agave is for the alcoholic beverage, tequila. This use of agave has an interesting heritage and involves unusual plant parts and processes. Prior to flowering, an agave plant accumulates high concentrations of sugars in the sap. Middle Americans (natives of Central America and Mexico) learned to identify this stage of growth in several Agave spp. and subsequently drain the sweet sap, called aguamiel. Although sometimes used as a beverage itself, aguamiel is more often processed into syruplike agave nectar, currently becoming popular as a natural sweetener. Aguamiel also is fermented to a mildly alcoholic drink called pulque. Middle Americans often cultivated the species best used for producing pulque.

Spanish colonists modified and added distillation to this process to ultimately develop tequila. In this scenario, the preflowering agave is harvested, the leaves are removed, and the resulting stem and leaf bases are cooked, chopped, fermented, and finally distilled into an alcoholic drink generically called mescal. Tequila is made by the same process, but legally "tequila" only refers to distilled mescal made from the species, Agave tequilana, in the Mexican state of Jalisco.

Despite its well-known beverage uses, historically, the primary use of agave and yucca has been for fiber. Leaf fibers were extracted and used to make cloth, rope, and baskets. Flowers, buds, some fruit pods, and flower stems were eaten raw or cooked. The stem and leaf bases of some Agave spp. were roasted and eaten, or dried to make sweet cakes. Roots of several species contain a mucilaginous substance used fresh or dried as soap. Trunks of yucca and various agaves have been used for fencing and cattle food.

In addition to the huge tequila industry in Jalisco, agave and yucca currently are cultivated as fiber crops and as ornamentals.

Agave Toxicities

Although agave has extensive food uses, it can contain toxic compounds. The juice or sap may contain needlelike oxalate crystals that can irritate the skin, mouth, tongue, and throat. Swelling of the throat, breathing difficulties, and burning can result. Furthermore, the juice, sap, and thorns can cause a skin rash or irritation. Finally, ingestion of some species of agave can cause stomach upset, vomiting, or diarrhea.

References

Florida Automated Weather Network (FAWN). 2010. http://fawn.ifas.ufl.edu/ (accessed January 17, 2010).

Fox, A. M., D. R. Gordon, J. A. Dusky, L. Tyson, and R. K. Stocker (2008) IFAS Assessment of Non-Native Plants in Florida's Natural Areas – Status Assessment. Cited from the Internet January 11, 2010. http://plants.ifas.ufl.edu/assessment/pdfs/finalassessjun05.pdf

Irish, M., and G. Irish. 2000. Agaves, yuccas and related plants: A gardener's guide. Portland, OR: Timber Press.

Kelly, J., and M. Olsen. 2006. Problems and pests of agave, aloe, cactus and yucca. AZ1399. Tucson: University of Arizona Cooperative Extension.

Thetford, M., J. L. Gibson, A. Santilli, B. O. Ballard, and J. K. Groninger. 2007. Succulents for southern gardens. Proceedings of the Southern Nursery Association Research Conference 52: 244-247.

Wunderlin, R. P. and B. F. Hansen. 2008. Atlas of Florida Vascular Plants. [S. M. Landry and K. N. Campbell (application development), Florida Center for Community Design and Research.] Institute for Systematic Botany, University of South Florida, Tampa. (http://www.plantatlas.usf.edu/; cited from the Internet January 11, 2010).