By Steven Hightower, Sonoma County Master Gardener
Spines, spikes, swordpoints—call them what you will—but the form of these leaf decorations and their striking geometric patterns are what make agaves some of the most interesting of succulents. Agaves have their own family, Agavaceae and are native to North, Central and South America and the West Indies. They range from small to enormous and take many different shapes and forms. Each agave plant consists of at least one rosette of stiff or fleshy leaves, almost always tipped with a spike and often armed with teeth. Leaves can be broad, spear-shaped, or long daggers.
Leaf color ranges from dark green to blue-green to blue-gray or gray, and leaves may be striped with cream, yellow, or lime-green. Margins or teeth are black or dark reddish. Many agaves develop branched spikes of yellow, white or sometimes pinkish tubular flowers, from several feet to as high as 30! Some bloom annually, although with some species it can take years for flowering to occur. After a stem flowers it dies, although often a number of small plants, called "pups", form around its base. These can be separated from the parent plant for propagation, or allowed to grow in situ and replace the dead stem.
The wide variety of sizes, shapes, and growth habits of agaves encourages a
number of garden uses. Large species, such as Agave americana, make dramatic statements as specimen plants, and other smaller varieties work well in combination with other plants in the garden or in containers. SCMG Anne Brewer, whose garden is featured this month, says “We have two Agave americanas - fabulous plants, but not for the faint of heart! They have beautiful form and make a strong architectural statement - bold visual punctuation. But be well aware that they sport razor sharp spikes at the ends of leaves and along margins, and they get huge--not for traffic areas. And it's very difficult to remove a large plant - be sure you plant it where you want it!”
Anne’s Agave americanas are planted at the bottom of her hillside garden, which slopes away from the house, providing a dramatic delineation between the garden and the orchard beyond. Their scale and strong form makes them effective even when viewed from afar.
Grouping multiple types of agaves in containers can also yield a dramatic effect, albeit a much smaller one. A container caution I’ve learned is that repotting can be tricky because of their lethal spikes and spines, as Anne has noted about the enormous A. americanas. In one instance I resorted to breaking the pot, as the agave had overgrown the container edges, and there was just no way to safely get it out.
Almost all agaves require full sun (at least six hours of direct sunlight) for best appearance and growth. They are tolerant of poor soils and don’t often develop nutrient deficiencies. However, soil with good drainage is essential. With our Sonoma Mountain clay, I grow most of mine in pots, with just a couple in the ground in well-draining mounds. Periodic water for container plants in summer is required, with frequency depending on variety and size and placement of the pot. Occasional summer water is necessary for established plants in the ground.
Most agaves that are available and suitable for us to plant locally are not bothered by many insect pests or diseases and are virtually trouble-free if sited properly.
If you want a crash-course in agaves, UC Botanical Garden in Berkeley has over 160 varieties in its collection. Ruth Bancroft Gardens in Walnut Creek is another good viewing spot. Agaves may be found at specialty succulent nurseries such as Lone Pine Gardens in Sebastopol, or at Emerisa Gardens in Santa Rosa, Cottage Gardens in Petaluma or Sonoma Mission Gardens in Sonoma.
Selected agaves, a number of which I have grown:
Agave americana (century plant) is one of the largest agaves--to 5-7 feet high, spreading to 8-12 feet. Leaves are blue to blue gray, with long sharp black terminal spines and wickedly toothed margins. Tolerates some shade and is drought tolerant, with occasional water in summer. It is relatively fast growing, and more so with extra summer water and is frost tolerant to 15-20 degrees. Very dramatic! This is a specimen plant, or for a very large container, in an area not near traffic. To quote SCMG Anne Brewer, it is "not for the faint of heart". A. americana ‘marginata’ is very sculptural, with dramatic, twisting green leaves with creamy yellow margins and grows to about 5-6 feet high and wide.
Agave attenuata (foxtail agave) lacks the genus’ normal physical danger, having no spines or teeth. Warning for most of us in Sonoma County: it is not reliably frost hardy, suffering damage below about 28 degrees. Medium green pliable sword-shaped leaves grow in a dense rosette. As it ages, it forms a smooth, curving trunk upon which the plant sits, unlike most agaves, whose rosettes stay low to the ground. This agave should have part/full shade except in coastal zones. It needs somewhat more water than most. I've had them badly damaged by freezes in the mid-high 20's, but come back again after a year or so. Its relatively delicate nature makes a nice contrast to its tougher spiny cousins. To 3-4 feet high if planted in the ground, smaller in containers.
Agave filifera syn. filamentosa (thread-leaf agave) grows to 2 by 2 feet in a sort of ball-shaped rosette with narrow leaves that sprout fine white threads on their edges, making it an interesting contrast plant. It takes full sun to light shade and is reasonably drought tolerant - occasional summer water. This species is hardy to about 20 degrees and is available in compact form in A. filifera ‘Compacta’.
Agave ovatifolia (whale's tongue agave) is a non-clustering agave that grows to around 3-5 feet tall and wide. Green to gray-green leaves (mine in container is green with a very slight yellow cast) that carry small teeth along the margin and end in a dark 3/4-inch spike. Takes full sun and is drought tolerant but will grow larger with some water. Frost hardy to zero degrees, and tolerates our wet winters better than any other agave species. It looks similar to Agave parryi, but with less distinct marginal teeth.
Agave parryi (Parry’s century plant) is one of my favorite agaves. Its blue-gray leaves have sharp black terminal spines and shark-tooth like margins. Most interestingly, those fleshy leaves carry the imprint of the leaf above and below, giving each leaf a distinct pattern. It grows to 1 1/2 feet high by 2-3 wide in the ground, and wants all the sun and heat it can get. It is frost tolerant to about zero degrees.
Agave shawii (Shaw's agave, or coastal agave) is another agave that is not reliably frost tolerant, with damage often occurring below 25 degrees. It grows in a clumping habit, with medium-sized dense rosettes to 2-3 feet tall and wide. Leaves are medium green, sometimes with reddish-black margins that carry sharp teeth and a lethal spine. Takes full sun, or part shade in the hottest locations. I grow it as a container plant, but its clumping habit would make it great for massing in the garden.
Agave utahensis (dwarf Utah century plant) forms dense clusters of small rosettes with gray-green, very thorny leaves with exaggerated sawtooth edges. The most northerly growing agave, it is distributed in the mountains of California, Arizona, Nevada and north up to Utah. One of the most cold hardy agaves, it is hardy to -10 degrees and prefers full sun. A semi-dwarf form, height and width to 1 1/2 feet
Agave victoria-reginae (Queen Victoria’s agave) is another very striking, geometric plant great for adding contrast to your garden. It forms a small, dense ball-shaped rosette with narrow dark-green leaves that are almost triangular shaped, with bright white spineless margins and ridge-markings along the leaves. This agave normally grows to
only a foot or so, making it a great container plant. Full sun to light shade in hotter areas. Frost tolerant to around 10 degrees.