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Agave shawii (Coastal Agave) - A medium sized clump forming California native agave that has rosettes with an upright form rising up to 2 to 3 feet tall by 2 feet wide with older plant suckering from the base to form large solid stands. The succulent dark gray green 1- to 2-foot-long leaves have large and attractive upwardly-curving and bent reddish spines along the margin and a short dark terminal spine. When a rosette reaches maturity, often after 20 years and during spring or summer months, a large stout inflorescence rises 6 to 14 feet from the center of the rosette with the top third producing sturdy reddish horizontal branches, each subtended by a long leafy purplish bract, that near their tips have umbels of red buds followed by yellow flowers. When this flowering occurs, the rosette that produced this inflorescence often takes on orange shade, then turning a light brown and finally gray.
Plant in full sun to light shade (requires shade in inland hot climates) in a well-drained soil. Little irrigation is required, and regular summer irrigation is harmful to this plant. From our experience we know it is cold hardy to at least 25° F - others note that damage to this plant can occur at around 23°F and that damage becomes extensive below 18° F. This is a great plant for massing at the top of a slope or at eye level where upright growth habit can be noted and when in flower will attracts many nectar feeding birds and bees. It is also useful for adding green color into otherwise grayer succulent gardens.
Agave shawii has become extremely rare in southern California, with the last documented natural populations within the US being a single cluster (one genetic individual) along the Mexico border at Border Field State Park and a cluster of plants along coastal bluffs on Naval Base Point Loma in San Diego. Some of the plants on the naval base at Point Loma plants are thought to be of natural origin while others were likely transplanted, and plants found elsewhere at other locations on Point Loma are thought to have been transplanted from these plants. Plants at the Torrey Pines State Reserve are also thought to be transplanted from elsewhere (Vanderplank, Sula. (2014). "A Conservation Plant for Agave shawii". Rancho Santa Ana Botanic Garden Occasional Publications Number 14.) Elsewhere in San Diego County urban development and wildfires have pretty much wiped out this plant's native coastal sage and chaparral habitats. It is fortunately more common in northern Baja California, where it grows from sea level to 1,650 feet in elevation from the border south to around El Rosario. Agave shawii subspecies goldmaniana is found further to the south from El Rosario south to Vizcaíno Bay and a bit inland along the slopes facing the Pacific Ocean. We also grow a variegated plant of this variety we call Agave shawii 'Marginata''. Another closely related species, Agave sebastiana, grows further to the south on the Pacific Baja islands and nearby mainland. It was previously considered a variety of Agave shawii.
The German born American botanist George Engelmann, who botanized and described much of the flora of northern Mexico, named this plant for his friend Henry Shaw (1880-1889), the founder of the Missouri Botanical Garden. Besides Coastal Agave this plant is also commonly known as Shaw's Agave. Our plants are from a planting in the desert garden at the Santa Barbara Botanic Garden that they received in 1939, but unfortunately there is no listing of provenance in their accession records for this planting.
This information about Agave shawii displayed is based on research conducted in our horticultural library and from reliable online resources. We also will relate observations made about it as it grows in our nursery gardens and other gardens we have visited, as well how the crops have performed in containers in our nursery field. We will also incorporate comments that we receive from others and we welcome hearing from anyone with additional information, particularly if they can share any cultural information that would aid others in growing it.
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