Tom Karwin, On Gardening | Great ‘candle’ in bloom

Popular Flower Types

Perennials bloom for many seasons and often come back year after year. Rudbeckia is a fall favorite that also adds color to the garden with its bright flowers. Heuchera is a shady garden favorite that attracts hummingbirds with its beautiful flower plumes.

The featured plant for this week’s column is “Our Lord’s Candle,” the name based on imagining its dramatic inflorescence as the flame of a great candle.

The plant has several other less visionary names: Spanish Bayonet, Chaparral Yucca, and FootHill Yucca. It’s also called Quixote Yucca, which might refer to its quixotic or puzzling relationship to the yucca. We’ll explore that relationship in a few paragraphs below.

This plant’s generic name, Hesperoyucca, translates to “false yucca.” The specific name, whipplei, refers to Amiel Whipple, a surveyor who worked in Southern California in 1853.

By April 12, 2023, the plant had reached its mature size, with its sharp-pointed leaves extending onto the public sidewalk. This photo shows the early stage of the flower stalk, which is about 6 inches in diameter. (Tom Karwin)

Hesperoyucca whipplei is native to coastal California and Baja California. Its natural range extends north to Monterey County. It grows fine in Santa Cruz County.

When first discovered, Our Lord’s Candle was considered to be a member of the genus Yucca. Archeologists determined that Native Americans used Yuccas as early as 5,000 years ago.

Still, this plant has subtle but significant differences from the yucca. Plant hunters recognized these differences in 1871, and many called it the false yucca. Recently developed DNA analysis has confirmed that this plant is genetically distinct from the Yucca. Taxonomists now identify the Hesperoyucca as its own separate genus, a relative of the Yucca, the Agave, and several other genera in the plant subfamily Agavoideae.

Hesperoyucca whipplei develops a dense, rosette-forming plant with fairly rigid, gray-green leaves that might be finally saw-toothed, with sharp tips. Online descriptions indicate various sizes of the rosette. The plant in my garden grew to about five feet high and wide.

The plant takes five to 10 years to reach its mature size. It then produces a rapidly growing flower spike up to an impressive 20 feet high, providing an impressive display in the garden.

The accompanying photos show different stages of growth of Our Lord’s Candle in my garden.

The plant’s pollination is a classic example of symbiosis. At night, the California Yucca Moth (Tageticula maculata) collects pollen grains from the blossoms, assembles them in a ball, brings the ball to the ovary of another plant, and deposits one egg into the ovary. The pollinated ovary then produces multiple seeds, providing a food supply for the larva. Amazing.

This photo, dated May 30, 2023, shows the structure of the plant's much-branched inflorescence, called a panicle. The branches are racemes, with flowers with short floral stalks (pedicels) along the branch's axis. The flowers open in succession toward the apex; some flowers are still in bud. (Tom Karwin) — This photo, dated May 30, 2023, shows the structure of the plant’s much-branched inflorescence, called a panicle. The branches are racemes, with flowers with short floral stalks (pedicels) along the branch’s axis. The flowers open in succession toward the apex; some flowers are still in bud. (Tom Karwin)

If this moth visits in my garden, it will need to find another Hesperoyucca whipplei to complete the process. Another specimen of this plant, a few blocks from my garden, is now in bloom, so pollination could occur. We should not underestimate the skill and determination of the California Yucca Moth.

Once pollinated, the plant will produce plenty of seeds in pods that will dry, fall to the ground, and split to yield the seeds to find their way into the soil. The plant has hundreds of blossoms, so it surely will produce plenty of seeds to survive the moth larva and fall to the ground to begin a new generation of Our Lord’s Candles.

Once the blossoms fall, the seed pods could be left on the stalk to support the development of the moth larva.

The plant is monocarpic: it dies after flowering. The sturdy stalk could remain standing for years and, for appearance, could be removed with the drooping leaves and root ball.

The plant will not produce offsets, as many other plants in the subfamily Agavoideae will do, but will rely on the development of seeds for propagation.

In time, we could see new plants sprouting in my garden. I would welcome the development of a new Our Lord’s Candle, but one would be enough. And I would support its growth a cautionary distance from the public walkway!

The individual blossoms are bell-shaped and creamy white, with green streaks. Photo dated May 28, 2023. On some specimens of this plant, the blossoms might be tinged with purple. (Tom Karwin)

Advance your knowledge

The print version of our recent column on Uncommon Fruit Trees dropped the common names of the plants in the photos. To see the common names for plant identification, browse to the online version —tinyurl.com/mr2v7wd2 —which includes the complete captions for the photos.

Mark your garden calendar

The Monterey Bay Rose Society has announced a two-stop Open Garden Tour for Sunday (this weekend!). The first stop, beginning at 11:30 a.m., will be at the MBRS Display Rose Garden, located at the Santa Cruz County Fairgrounds, 2661 E. Lake Ave., Watsonville (enter via the Livestock Entrance). Potluck lunch while viewing the plants.

The second stop will be from 1-3 p.m. at the home garden of MBRS member Janey’ Leonardich, 940 Green Valley Road, Watsonville. Desserts and beverages will be available.

MBRS members will be available at both gardens for comments and questions.

Tour participation is free for MBRS members and $15 fee for non-members. For more information, call 831-320-5503 or email jtruskot@comcast.net.

The Ruth Bancroft Garden & Nursery will present the webinar, “Landscape Sketching 101,” at 10-11 a.m., June 17. “Landscape sketching is an indispensable tool for designers to communicate the look and feel of the proposed design to the client. Learn the steps on how to successfully create a simple but effective sketch and perspective drawing regardless of your artistic abilities.” This class is included in the Dry Garden Design Certificate Program. Registration is $15 for Bancroft Garden members and $30 for non-members. The webinar will be recorded and registrants will have seven days to watch the presentation.

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.