Spiking Interest
by C. Colston Burrell

Plants with bold, spiky foliage can make a ho-hum garden exciting. Here are some noteworthy choices you can integrate into your landscape.

When designing and planting our gardens, most of us tend to focus on flowers first. But to be successful, a design must rely on structure—the “architectural” elements of form and texture, shape and height. Strong form, along with the plant’s texture, give a garden season-long interest.

In profile, the majority of garden plants have an even, rounded form. Like a sky filled with billowing clouds, these mounding forms are satisfying to the eye, but too much of a good thing quickly makes a vignette mundane.

Sharp edges make sharp contrasts, creating essential tension in planting design. Tension in design comes from a balanced relationship and interplay between strongly opposing elements, which causes both elements to achieve greater prominence. Ascending swords, spears, and lances make lasting impressions. Vertical lines draw the eye skyward, which breaks the horizontal lines of the planting and animates the entire garden picture. Hand in hand with form, the texture of foliage creates visual excitement that makes a successful design….

Desert Suite

The unfolding rosette of Agave parryi (USDA Hardiness Zones 7–10, AHS Heat Zones 12–5) foliage makes a lasting impression on the eye. Its rosettes are squat and rotund, ultimately attaining one to two feet. When the flower finally arrives, it rises to six feet or more, and sports more than 100 upright yellow flowers in tight tiers. Although each rosette flowers only once, offsets, or pups, may form from the crown before the rosette dies. Among the hardiest of the agaves, A. parryi thrives in sandy soil. A sloping site is ideal, where excess water will drain away from the crown. Full sun to light shade is best. Several subspecies have been named, each with a different form and size. Additional gardenworthy agaves to consider include A. americana, A. gracilipes, A. havardiana, A. montana, A. neomexicana, and A. scabra. Take care, particularly if you have children, where you site agaves that have stiff, sharp spines at their leaf tips, because they can pierce the skin.

The twisted powder blue blades of blue sotol or desert spoon (Dasylirion wheeleri, Zones 7–10, 11–7) are lined with teeth reminiscent of the snout of a sawtooth shark. Roughly spherical in outline, mature crowns reach four feet in height, and give rise to towering, 10-foot spires of densely packed cream-colored flowers. This dioecious genus flowers annually, unlike many other desert lilies.

A southwestern desert native, sotol, grows best in well-drained sites with average sandy or loamy soil. Good drainage is essential, and avoid organic mulches, which can retain water around the crown of the plant. Prized for xeriscape gardens, this exquisite plant has a grace lacking in the more menacing agaves and yuccas. The long blades that surround the spherical crown dance in unison in the wind, and the flowers are favored by insects. Dasylirion texanum (Zones 9–11, 11–9) has unarmed green leaves and narrow bloom spires, while the spineless filamentlike foliage of D. longissimum (Zones 8–11, 11–8) forms a unique, fine-textured crown.

Yuccas are quintessential spiky forms, familiar in old gardens, cemeteries, and along roadsides. Adam’s needle or Spanish bayonet (Yucca filamentosa, Zones 4–11, 12–5)is widely distributed in the East, and has a variety of brightly variegated forms. They grow from woody crowns with fleshy roots. The nodding, creamy-white flowers have three petals and three petal-like sepals that form a bell. Erect, multi-branched bloom stalks rise five to 15 feet above the stiff, two- to two-and-a-half-foot needlelike leaves…

Plants That Like Wet Feet

Though the desert springs to mind when thinking of spiky forms, many moisture-loving plants also feature spiky foliage. The narrow ridged blades of sweet flag (Acorus calamus, Zones 3–8, 9–4) are easily overlooked in the sunny wetlands where it grows wild across the northern hemisphere. In the garden, however, sweet flag, most notably white-striped ‘Variegatus’, is a knockout. Sweet flag is distinctive for the strong citrus odor of its crushed leaves and rhizomes. It’s at its best in water gardens or ponds, where the flat fans of leaves ascend three to four feet. Plant sweet flag in fertile loamy soil or in containers in full sun or part shade. Contrast the verticallity with flat, floating leaves of water lilies (Nymphaea spp.) or bold pickerel weed (Pontederia cordata). For diminutive spikes in sun or shade, Acorus gramineus (Zones 5–8, 9–5) forms a carpet of arching fans in green or in brilliant yellow stripes in the selection called ‘Ogon’. Plants thrive in water or equally well in rich, moist garden soil.…

In most of the United States, gardeners make do with a few potted New Zealand flax (Phormium tenax, Zones 9–11, 12–2) scattered outdoors in summer in sunny spots where a bit of panache is required. But West Coast gardeners enjoy them as year-round additions to beds, borders, and containers. A range of warm foliage colors makes New Zealand flax cultivars the most sought-after spikes for curb appeal and seasonal drama. Tangarine, apricot, cerise, rose, and chartreuse are a few of the colors presented by the striped foliage. Often, multiple colors appear in a single variety. This species is native to peatlands and along stream courses adjacent to grasslands in temperate New Zealand. Plants demand even moisture and in cultivation seem to also need excellent drainage in full sun to light shade. Despite their native haunts, in containers waterlogged soil and wet crowns are sure death.…

Designing on the Edge

Vertical forms fit into gardens in a variety of ways. To place specimens as focal points, visually divide the depth of the garden space into thirds. For an intimate feel, place a specimen one third of the way from the viewing point. For a more expansive feel, accentuate the perspective by placing the plant two thirds of the way into the space.

Use yuccas and their kin to mark the corners of beds. Contrast is the key to effective display…

Photo credits: Phormium by Saxon Holt

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