Posted by Aaron Barton on Apr 6th 2023
Yucca (Adam's Needle)
The perfect perennial for gardeners longing for warmer climates and sunnier days, Yucca filamentosa (YUK-uh fil-a-men-TOH-sa), or Adam’s Needle, is an exceptional perennial far from the usual suspects found in midwestern perennial gardens. Belonging to the asparagus family, Asparagaceae, Adam’s Needle is a low maintenance evergreen shrub that thrives in difficult sites where most other perennials would struggle to survive, tolerant of poor soils, drought, and exposure to deicing salts, and resistant to deer and rabbit feeding.
Native to beaches, dunes, and fields of the southeastern United States, with the true native species reaching exceptional heights upwards of ten feet tall when flowering, common Yucca cultivars grow to a far more manageable size of two to three feet tall and wide, with bloom stalks extending beyond the foliage. Forming an attractive rosette of rigid, sword-shaped, blue-green or variegated green and yellow leaves upwards of 24” long, capped with sharp spines, Adam’s Needle provides excellent tidy foliage interest, producing basal offsets to form an impactful colony over time. Adding to their textural appeal, the leaf margins, as their specific epithet filamentosa implies, have fine white, thread-like tissues that curl up along the leaf margins for wonderful added interest. Contributing to their resiliency and exceptional drought tolerance, Adam’s Needle also establishes deep, fleshy taproots that will not transplant well and should not be disturbed after planting.
Blooming from mid-summer through late summer, Yucca sends out impressive spires several feet above the basal foliage, forming rigid terminal panicles upwards of five feet tall with numerous ivory white nodding, bell-shaped blooms. Stunning when massed together, their distinct blooms are only able to be pollinated by the yucca moth (Tegeticula sp.), coevolving together as the moth’s reproductive host plant, and depending on one another for survival in unmanaged settings.
A fascinating coevolutionary relationship, Yucca have even evolved to manage these moth populations as well, assessing their bloom weight and ovule damage from moth oviposition (egg insertion), to selectively abscise (drop) blooms that are exceptionally heavy from an overabundance of moth eggs. However, one species of Yucca moth, Tegeticula intermedia, has evolved to avoid depositing their eggs directly into the ovule to circumvent this mechanism employed by Yucca filamentosa. The moth instead opts for superficial oviposition, a reproductive practice where eggs are deposited shallowly, just below the tissue surface instead of fully into the ovule of the flower. The female moth even goes as far as to deposit their eggs one at a time instead of all at once to deceive the Yucca plant and avoid it sensing the abundance of eggs and aborting the bloom. Mature Yucca moths mate on the blooming flowers, typically at night, whereafter they deposit their eggs. While most species will also pollinate the flowers, T. intermedia and other species also exhibit “cheating” behavior and are considered a parasite to the plant, using Yucca as a reproductive host without so much as pollinating their blooms, adding to their interesting evolutionary saga.
Hardy, and carefree, Yucca filamentosa thrives in full sun sites in a wide range of soil conditions so long as sites are well-drained. Adam’s Needle is stunning when mass planted and ideal for adding height and structure to waterwise landscapes, boulevard plantings, sunny borders, and dry sunny slopes.