Tom Karwin, On Gardening | The many forms of agave

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Whether you are a beginner gardener or seasoned pro, these flower varieties will bring your yard to life. Find seeds, fertilizer, and a variety that fits your needs and climate.

With its sunny petals and symbolism of rebirth, the daffodil is the embodiment of spring. The elegant iris symbolizes faith, hope and power and makes a striking gift.

It has been over a year since reviewing my agave collection, so today’s column checks out the development of selected specimens and compares the form variations of these popular plants.

Agaves are succulent plants native to Mexico and Central America. The genus now includes about 252 species, after taxonomists included some related genera previously regarded as separate. The popularity of these has encouraged growers to introduce many cultivars, including both selected varieties and hybrids.

Cream Spike Agave (Agave applanata 'Cream Spike') This plant has variegated leaves and rich chocolate-colored spikes. It grows to just 12 inches wide and generates many offsets, as shown in this photo. It has an unclear origin and is sometimes referred to as Agave patonii 'Alba Marginata'. (Tom Karwin) — Cream Spike Agave (Agave applanata ‘Cream Spike’) This plant has variegated leaves and rich chocolate-colored spikes. It grows to just 12 inches wide and generates many offsets, as shown in this photo. It has an unclear origin and is sometimes referred to as Agave patonii ‘Alba Marginata’. (Tom Karwin)

All Agaves have leaves that form into rosettes. Their leaf clusters range in size from one foot high and wide to up to six feet high and wide, with flower stalks rising well above the leaves.

Most Agave species have sharp terminal spines, sharp marginal teeth, or both. These present a fierce appearance and require careful handling, but some gardeners find them appealing and uniquely attractive.

Agaves might be regarded as similar to the Aloes of South Africa, which are also rosette-forming. A significant difference is that Aloes lack the spininess of the Agaves.

The photos in today’s column show plants from my garden, selected for varied forms.

Agaves propagate in two ways: generating rhizomatous suckers (called “offsets” or “pups”) or seeds.

Propagation by offsets

Once they become mature, most Agaves produce pups. The quantity of these offsets varies with the plant’s species, age, and environment, and whether it’s growing in the ground or in a container. Most Agave species produce many offsets and eventually form into clumps.

Some Agave species, when growing in habitat, produce few offsets or none. These are called “solitary” Agaves. When cultivated, however, even these could produce some offsets.

Some gardeners appreciate Agave offsets and welcome the growth of clumps. Otherwise, they occasionally separate and replant the offsets to form a community of the given species. Another option is to give or sell the offsets to other gardeners.

Variegated Fox Tail Agave (Agave attenuata 'Variegata') A variegated form of the spineless Agave attenuate, grows slower than the species, and will eventually reach three feet tall and four feet wide. The offsets are often in high demand. The wide pale green pliable leaves have marginal yellow stripes that vary from leaf to leaf. (Tom Karwin) — Variegated Fox Tail Agave (Agave attenuata ‘Variegata’) A variegated form of the spineless Agave attenuate, grows slower than the species, and will eventually reach three feet tall and four feet wide. The offsets are often in high demand. The wide pale green pliable leaves have marginal yellow stripes that vary from leaf to leaf. (Tom Karwin)

Other gardeners prefer solitary Agaves and limit their collections to non-pupping species.

Collectors have posted lists of solitary Agaves. For example, Starr Nursery listed 66 solitary or nearly solitary Agave species: starr-nursery.com/solitary-nearly-agave-species/.

Agave seeds

When an Agave plant becomes sufficiently mature, its rosette generates a flowering stalk from the center of the plant. Some plants might require several decades before producing such a stalk, which will produce multiple tubular flowers (which require pollination) or vegetative bulbils (a form of asexual reproduction).

The flowering stalk can grow up to 40 feet high, depending on the species.

After producing either seeds or bulbils, the rosettes of most Agaves will die. Such plants are called monocarpic. A few species are polycarpic, meaning that they will flower and set seeds many times before dying.

Because of the rich variations of their rosette sizes, leaf shapes, and leaf colors, Agaves can be intriguing plants for collectors. A purist collector might focus on the natural species, while an adventurist might enjoy adding new hybrids to the garden. In either case, the spines, which can be handled safely with appropriate care, add to their unique aesthetic quality.

Agave horrida This plant has a symmetrical solitary rosette that reaches two feet tall by three feet wide. It has mid-to-dark green leaves with recurved brown teeth along the margins. With age, the teeth bleach out to gray, contrasting against the darker green leaves. The specific epithet is from the Latin word meaning "bristly." (Tom Karwin) — Agave horrida This plant has a symmetrical solitary rosette that reaches two feet tall by three feet wide. It has mid-to-dark green leaves with recurved brown teeth along the margins. With age, the teeth bleach out to gray, contrasting against the darker green leaves. The specific epithet is from the Latin word meaning “bristly.” (Tom Karwin)

Advance your knowledge

To view a wide range of Agave plants, visit Calflora, a nonprofit database providing information on wild California plants calflora.org/search.html, and search for “agave” to see all plants in the genus, or search for Agave with a specific name to see a plant of interest.

Calflora has invited your votes for plant photos that are candidates in its Ninth Annual Photo Contest. The entries have been provided by plant lovers who have selected their most competitive pictures.

Click on https://tinyurl.com/rf9ffkhb to view the candidates. Scroll down for a link to a brief video tutorial on how to cast your votes.

Tom Karwin is a past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a past president and Lifetime Member of the Monterey Bay Area Cactus & Succulent Society, and a Lifetime UC Master Gardener (Certified 1999–2009). He is now a board member of the Santa Cruz Hostel Society, and active with the Pacific Horticultural Society. To view photos from his garden, https://www.facebook.com/ongardeningcom-566511763375123/ . For garden coaching info and an archive of On Gardening columns, visit ongardening.com. Email your comments or questions to gardening@karwin.com.