While California’s persistent drought does not have a gardener’s attention these days, we should assume that it will return. Both drought and unusual rains could be indicators of climate change.
The gardener’s long-term adjustment to climate change generally involves favoring plants that grow well under higher average temperatures than one has experienced in the past.
That’s a minimal response to a complex matter, but gardening in a moderate climate such as the Monterey Bay area suggests trending toward succulent plants. These are plants that have evolved to manage irregular access to moisture and to thrive under warmer temperatures.
That brings us to today’s topic: an overview of the agave, a popular succulent plant genus, with a summary of common characteristics of the species within the genus. These species display a wide range of variations, some of which are shown in today’s photos.
The Variegated Caribbean Agave (A. angustifolia var. marginata) is a typical media-sized Agave with stiff, sword-shaped leaves. It grows to 20 inches tall and 30 inches wide. (Tom Karwin)
The genus agave has been defined as a paraphyletic group, meaning that it combines different plants with a common ancestor. These include the original agave genus, plus Manfreda, Polianthes and Prochnyanthes, which had been considered separate genera. The expanded genus includes some 250 species, all of which are native to Mexico and other hot and arid regions of the Americas and the Caribbean.
All agaves are rosette-forming succulent plants. In botany, a rosette is a circular arrangement of leaves or structures resembling leaves. In flowering plants, rosettes usually sit near the soil. The architectural quality of the agave rosettes makes them desirable additions to the garden landscape, either as prominent highlights or as contrasts with other plant forms.
Agaves are almost always acaulescent, meaning that they have no stem or appear to have none. Exception: one popular species, the Foxtail Agave (A. attenuata) develops a stem up to five feet tall.
All agaves develop a flower spike. The individual species determines the height of the spike (which can reach up to 40 feet) and the maturation period before the spike develops (at least about 10 years, and can be up to 60 years). Some spikes are branched; others are unbranched (spicate).
Most agaves are monocarpic, meaning that they produce flowers, seeds and fruits once in their lifetime and then die. A few exceptional species are polycarpic: they do not die after flowering and fruiting. Though they flower only once, they have more energy to reproduce. A polycarpic specimen in my garden is the uncommon Maguey of the Mist/Maguey de la Niebla (A. polyacantha).
The Cream Spike Agave (A. applanata “Cream Spike”) has a compact rosette about only 1 foot high and wide. This variegated cultivar is shown in contrast to a Blue Lechuguilla (A. funkiana “Fatal Attraction”), which also has variegated leaves. (Tom Karwin)
Most agaves propagate before flowering by developing rhizomatous suckers at the base of the rosette. Exceptions that do not produce such offsets (or very few) are called “solitary.”
Most agaves have sap that contains oxalic acid crystals that can become embedded in the skin, causing “agave dermatitis,” with a severity that varies depending on the individual’s susceptibility. Good advice when cutting agave leaves: wear wrap-around eye protection, long sleeves, pants, and gloves, and cover your hair; do not wipe your face with sleeves or other fabric that may have bits of the plant or sap on it; use a hand saw instead of a power saw, which can spray sap.
Variations of agave foliage
Each of the 250-plus species in the genus agave (including the sub-genera) has unique features, making the genus appealing to succulent plant collectors. This section lists major kinds of variation, which can occur alone, in two or more combinations.
• Size: Agave rosettes range greatly in size. The smallest is the Smallflower Century Plant, also called the Santa Cruz Striped Agave (A. parviflora), a rare species from southeastern Arizona and northern Mexico . It grows 4-6 inches tall by 6-8 inches across. One of the largest is the Maguey Verde Grande (A. atrovierens), with leaves nearly 15 feet long and 16 inches wide. The more familiar American Century Plant (A. americana) grows a rosette 6 feet tall and 10 feet wide.
Most agave have solid-colored leaves in shades ranging from green through bluish to silver-gray. Some species have mutated variegation and some hybrids have been developed with attractive striping, typically yellow or creamy colored.
The Foxtail Agave (A. attenuata “Variegata”) is one of the few spineless Agaves, making it popular for spine-averse gardeners. This cultivar also has variegated leaves. (Tom Karwin)
Most agaves have sharp terminal spines (at the ends of leaves), and some also have marginal spines (along the sides of leaves) as protection from predators. Many succulent gardeners see Agave spines as fascinating features; others regard them as simply hazardous. Some caution is needed during routine handling of agaves. For example, wrapping an agave in an old towel while planting or transplanting is a simple safety practice. Spineless exceptions, popular with spine-averse gardeners, include the Foxtail Agave (mentioned above), members of the sub-genus Manfreda, and most Agave/Manfreda hybrids, called Mangaves.
• Leaf form: Agave rosettes vary between compact and open forms. Some of the open forms have stiff, sword-like leaves, and others have gracefully curving leaves. For example, the Octopus Agave (vilmoriniana) has leaves that curl inwards at their tips. Producing a very unusual yet attractive look.
• Leave width: The leaves of various agave species vary from wide to narrow. The most familiar varieties have tapering leaves two or three inches at their widest, while some varieties have narrow, quill-like leaves. An example of the latter is the Hedgehog Agave (A. stricta), which is described as having “narrow, evergreen, yellow-green, green or glaucous blue, square to roundish in cross-section, toothless on the margin, about 14 inches long; thick at base, then narrowing to end in a very sharp spine.” The “rubra” variety has reddish leaves, with a striking appearance.
Advance your gardening knowledge
A recent new book on agave varieties is “Agaves: Species, Cultivars & Hybrids,” by Jeremy Spath and Jeff Moore. This book, and other good books by Jeff Moore, has been available to order online at solanasucculents.com.
The Cactus and Succulent Society of America will present the webinar “Your Dreams Have Come True at 10 a.m. Saturday. The presenter will be Petra Crist, the owner of the Rare Succulents Nursery in Fallbrook. For information and to register for this free event, visit cactusandsucculentsociety.org.
The Garden Conservancy will present a virtual talk by next-generation landscape designer Lily Kwong at 11 a.m. Jan. 26. Kwong has roots in the urban planning and art worlds with a mission to reconnect people to nature. She specializes in creating transformative environments that combine horticulture, design, education and visual arts to create cultural experiences that harmonize people with their environment. She earned her degree in urban studies from Columbia University and is an important voice in the growing sustainable movement. She serves as landscape editor for Cultured Magazine and is also a member of the NEW INC program, the New Museum’s incubator. Her botanical art installations have been featured on The High Line, Grand Central’s iconic Vanderbilt Hall, The Whitney Museum shops and more.
This event is the second webinar in the conservatory’s winter 2023 virtual programs, which are fee-based. The cost is $5 for conservancy members, $15 for general admission. For registration and additional information, visit gardenconservancy.org.
Enjoy your garden!
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 daily photos from his garden, https://www.facebook.com/ongardeningcom-
566511763375123/. For garden coaching info and an archive of previous On Gardening columns, visit http://ongardening.com.
The Mexcalmetl (A. Horrida) exemplifies the “wicked” spines that might discourage some gardeners while providing unique appeal for others. It grows 1 to 2 feet tall by 2 to 3 feet wide. “Horrida” means bristly, prickly, or rough. (Tom Karwin)