Landscapes designed and populated with Southwest native plants are in sharp contrast to the more foliage intense English, eastern, southern, Pacific northwest and northern areas. Typically, the evergreens in those landscapes feature shrubs with many needles or leaves. Overlooked evergreen plants of the southwest landscape are often a succulent, a plant with living tissue that is able to temporarily store water allowing it to be independent of another water source through periods of drought or low rainfall. Plants of a succulent nature are found in nearly every genus; the whole of the plant need not be succulent for the plant to be considered a succulent. For instance, the roots, stems or leaves may be the succulent feature. Examples of root succulence are tuberous roots, corms, rhizomes and bulbs.

Many succulent plants open their stomata for gas exchange at night and store carbon dioxide. By day, while the stomata are closed, photosynthesis is conducted using the stored carbon dioxide (http://www.desertmuseum.org/programs/succulents_adaptation.html). This system is called Crassulacean acid metabolism or CAM photosynthesis, first named after the Crassulaceae family of succulents. CAM photosynthesis allows for these succulent plants to conserve water by closing their stomata during hot daylight hours, an adaption to dry and hot environments. Some succulents are even able to close there stomata rather permanently, called CAM-idling, however this does not allow for any growth of the succulent, merely maintaining the status quo, which in arid regions, is an important trait. Herbaceous plants operate on the reverse system, with their stomata open during the day.

Although low in percentage to herbaceous or woody plants, succulents populate many regions of the world, particularly semi-arid to arid climates, including the American Southwest, Mexico, Central and areas in South America, Australia, Western and Central Asia. South Africa and Madagascar are notable for the diverse numbers of succulents, a few are cold hardy in the Texas Panhandle. Our Southwestern succulent evergreens include a selection of agaves, cacti, most yuccas and other non-native succulent plants (sedums) that thrive in the Texas Panhandle. Virtually untapped as a means of winter green and winter interest, our native evergreen (or ever-blue, ever-gray) succulents can easily be incorporated into native, low water-use, Western cottage and rock garden designs and styles. Agaves, yuccas and cacti were greatly prized and imported from the New World to the Old in the early days of North American exploration by the Europeans, having readily naturalized throughout the greater Mediterranean region.

Agave

Agaves are desirable in the Texas Panhandle landscape for their architectural stature and interesting leaves. Leaves of the agaves grow from a central basal rosette and are long-lived, often 12-15 years, holding in water and energy. The leaves are the storage units, you might say.

Agaves are native to the United States, Mexico, Central America, Venezuela, Columbia, Brazil and some islands in the West Indies. It is thought there are from 200 – 250 species within the genus Agave. Linnaeus first described the genus Agave, a Greek word meaning “noble”, in 1753. Since 1866, there has been much shifting of genera into and out of the Agavaceae family. Today, Agavaceae consists of 19 genera, including Agave, Cordyline, Dasylirion, Dracaena, Furcraea, Hesperaloe, Manfreda, Nolina, Polianthes and Yucca.

Agaves are found growing from sea level to over 7000 ft. in elevation in deserts, along the coasts in wooded /shaded areas, dry, rocky hill and mountain sides and of course, the arid plains. Even though the natural locations for agaves are much further south of Amarillo, and therefore assumed to be adapted to warmer climates than ours, those agaves that grow in higher elevations (4500 – 7000 ft) could be cold hardy for the Texas Panhandle. Agaves native to temperatures on the desert floors would not survive our colder winters without adequate protection -- these are suited to container gardening.

Agaves are readily paired with native shrubs and wildflowers. A bed combination for long season of interest would be a cold-hardy agave; a Chisos Rosewood, Vauquelinia corymbosa, var angustifolia (a SW native evergreen tree); Englemann's Daisy; Flame anisacanthus, Anisacanthus quadifidius var. wrightii; Liatris punctata, Gayfeather and Penstemon pseudospectabilis, snapdragon or desert penstemon; paper flower, Psilostrophe tagetina; prairie verbena, Verbena bipinnatifida; Desert Zinnia, Zinnia acerosa; and one of the globe mallow varieties of Sphaeralcea ambigua. Add a nice sized rock or boulder for accent.

Form and Stature

Since the leaves of agaves are so long lived, one of the most remarkable characteristics is the bud-imprint. Buds may take up to 2-3 years to unfurl. In species with teeth, these enveloped buds impress themselves on the surrounding leaves. I have watched my larger agaves grow and unfurl, an activity savored over many months year to year. Agaves with thinner leaves alternately stiffen and become flaccid as their water content rises and falls. To me, they are a plant of great beauty, majesty and interest with endless variations from species to species. The texture and nobility of agaves begs for it's leaves to be caressed, carefully.

Nearly all leaves of the agave are glabrous, that is, without hairs. Many agaves have teeth along the margin, well defined from the leaf, and nearly all have a terminal spine. One main differences between agaves and aloes is that with aloes, what appears to be teeth are just elongations of the leaf.

Century Plant is the common name for agaves. Agaves won't flower for many years, usually far short of 100 years, but perhaps in 10 - 20 or more. Being monocarpic, they flower and die. So much energy is channeled into this reproductive stage, the plant dies and hopefully lives on through its seed and offsets. If the leaves themselves weren't enough reason to grow agaves, then certainly this once in their lifetime occurrence would entice you to use them. The asparagus-shaped flower stalk is several inches thick and rises up from 6 (in the smaller species) to forty feet.

Agaves are divided into two main groups, or subgenera: Littae and Agave. Agaves in the Littae subgenus include species with spicate inflorescences (unbranched arrangement of flowers attached directly to the stalk). Species in the subgenus Agave have paniculate inflorescences (branched arrangement of flowers), similar to a candelabra. Flowers are fragrant and begin to open from the bottom on up and flowering may continue for up to 2 months. Many agaves also reproduce by offsets or pups, but not all.

Agave Culture

Agaves like sunny locations and will grow well with partial shade, especially afternoon shade. In a native setting, you'll often find agaves under the shade of a tree or another plant. Soil with good to excellent drainage and low organic matter is needed, or as it is sometimes referred to, mineralized soil. Heavy clay soil needs to be very well amended with inorganic amendments for increased drainage. Inorganic amendments are greensand, lava sand and granite sand. One technique used to increase drainage is to mound the plant, that is, build up a mound of gritty soil to insure good drainage. I've see rather humpy beds of agaves in rainy locations.

Certain agaves actually require a high alkaline/caliche soil for optimum appearance. Everyone seems to want to grow plants not native to their area. A friend of mine, though from a warmer, southeastern Texas location with sandy loam soil, wanted to grow agaves. He built an agave/cactus bed, hauling in several cubic yards of caliche, at a cost of $90/cu/yd. as the base soil. An Agave victoria-reginea 'King Ferdinand' was planted in his normal soil. Agave victoria-reginea is thought to be one of the prettiest, certainly the most handsome of agaves, with a tightly formed rosette of thick, triangular leaves marked with white ('King Ferdinand' has larger leaves, not quite as tight a rosette). That particular agave lost its coloration. He was so disgusted with it, he pulled it out of the ground and gave it to me, saying for me to plant it in caliche (I hesitated to suggest he just plant it in his caliche bed). About a year after following his advice, the coloration started to return. After two years, it looked normal again. 'King Ferdinand' is now the size of 20-24 inches wide by about 18 inches high.

The soil mix does make a difference. You can't go wrong with gritty, sandy, calcareous soils. Although most agaves are grown in areas with alkaline soil, they respond better in growth and appearance with rain water or dechlorinated tap water acidified with white vinegar or citric acid to approximate rainwater, a pH of 5.6 (1 tablespoon vinegar to 5 gallons tap water).

Expect differences in the leaves and even shape of the plants depending on your climate, as well as your soil. Cooler climates than their native habitat, cultivation practices, moisture and pot culture, if in containers, alter the appearance from the native grown in situ. The agaves may not even flower. An absence of pollinators specific to the agave may prevent flowers from producing viable seeds, if they do flower. This variation in location and culture has lead to a bit of confusion in naming varieties and even species, over the decades. Unless you're a serious collector, it's best not to be disturbed by agaves shifting from one subcategory, genus or species to another by the international Committee on Botanical Nomenclature.

Agaves can be watered frequently during the summer or not. The Texas Panhandle usually receives ample summer moisture for normal agave growth without supplementation, but it won't hurt agaves to be watered weekly, provided the soil drains well. Many agaves are suitable for container growing that needs to be wintered over in a protected place to prevent frost and freezing. The soil mix should be coarse, gritty, low in organic content and drain well. Container agaves could be watered weekly during the growing season.

Agaves do grow in elevations and on slopes that are subject to occasional light snowfall. Snow is usually light, and melts quickly, running down slopes. The most important factor to remember in wintering over agaves outside is to keep them dry. That is, NO winter watering. Heavy snows may cause root rot. In climates colder than their natural habitat, it may be necessary to build up the soil in mounds with the agaves planted on the top to aid in drainage. Good to excellent drainage is key to overcoming winter moisture in climates within agave tolerances.

Cold Hardiness

I'm sure I'm not aware of all the agaves that are cold hardy for the Texas Panhandle. Cold hardiness depends on a number of factors, not just the minimum recorded low temperature. Younger, immature agaves are generally more cold hardy than older, more mature plants. Agaves given proper care and placed in advantageous locations and soil will survive, while others of the same species may not under different care and location. If the listed temperature range given is within 10° of your average winter low temperature, I think, if you'd like to try to winter over outside an agave species, follow the recommendations and see. Individual testing is, after all, really the only way we'll know for sure. And results could vary from year to year depending on weather.

In researching the cold hardiness of agaves, the lowest range of temperatures given often varies. This is due, in part at least, to soil texture, organic content and winter moisture. You will achieve good results with soils that have very good drainage and low organic content. One final reminder – no winter irrigation.

Low temperatures given are from the following sources:

• A. Mary and Gary Irish, Agaves, Yuccas and Related Plants, Timber Press, 2000.
• B. Mountain States Nursery catalog
• C. High Country Gardens catalog
• D. Personal Experience (through April, 2013)
• E. Judy Mielke, Native Plants for Southwestern Landscapes, Univ. of Texas Press, 1993.

Agave Species to Try

This is a starting point of agaves to plant in ground, for wintering over outside, and are within the range of the average low temperature for most of the Texas Panhandle.

Agave cerulata, 10° (A), Have not tried it.

A. havardiana, -10°, (A), (C), (D) Yes, has wintered over for 7 years.

A. lechuguilla, 0°, (A), (D) Yes, wintered over 5 years so far.

A. lophantha, 10°, (A), (B). Have not tried it.

A. montana, 10°, (B). I have not tried it.

A. murpheyi, 10°, (A), Have not tried it.

A. neomexicana, -20°, (A), (C), (D), Yes, wintered over 7 years.

A. palmeri, 10°, (A) Have not tried it.

A. parryi, -20°, (A), (D). Yes, wintered over 7 years.

A. parryi var huachucensis, 15°(A), (D). Questionable, made it through a few winters, but did die. Most likely needs better drainage.

A. parryi var truncata, 15°, (A), (D). Tried 3 of them and they all froze.

A. parviflora, 10°, (A). Have not tried it.

A. salmiana, 5°, (A). Have not tried it.

A. scabra, 10°, (A), (B), (D). Wintered over 1 year good. Second year froze back to the roots but re-grew. Keep snow off of it to prevent dieback. It died the third year. Most likely needed soil to drain better.

A. schottii, 10°, (A), (E). I have not tried it.

A. toumeyana var. 'Bella', 10° (A), (C). Flowered and died after flowering first year I bought it. Needs a longer trial.

A. utahensis, all varieties, 0 – 10°, (A) Have not tried them yet.

A. victoria-reginae, 10° (A), (B), (E). Planted a small, 4 inch specimen in a protected location facing south 3 winters now. Outer leaves froze this third year, but plant still lives. Have not tried to winter outside a larger specimen of A. victoria-reginae. They winter over in Albuquerque.

If you are unsure whether your agave species will tolerate our winters, pot it up instead of in the ground. Agaves make stunning container plants, mostly by themselves, or in a grouping with other succulents. I also have several agave species not listed here and other succulents that I keep in containers and winter over indoors. Any agave can be container planted, some of them get quite large (Agave americana species) and need to be repotted every few years. In fact, some will grow so large, you may have difficulty moving the pot and finding a place to winter them over.

Angie Hanna, April 23, 2013