University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article
Dr. Leonard Perry, Extension Professor
University of Vermont
In New England, distinctive trees and shrubs are given the Cary Award.  Named for a Massachusetts nurseryman, and administered by the Tower Hill Botanic Garden, this award is given to several winners each year as judged by a panel of professionals.  These are either new plant introductions, or others that aren't new but deserve wider use in landscapes. The two winners for this year include a rose and a yucca—shrubs, but which are often grouped under perennials even though their tops generally don’t die back to the ground in winter.

Adam’s needle or yucca (Yucca filamentosa) has a quite interesting and different habit, consisting of long sword-shaped leaves with sharp tips (use eye protection when working around them, and keep children away).  Flowers in June and July are on stalks to 7 feet high above the basal leaves, which are only up to 2 feet high.  The large and creamy white bell-shaped flowers are held in large open clusters of several dozen flowers, making quite the show. The sweet scent of flowers attracts a pollinator in native areas— the very small yucca moth.

Although evergreen in winter, in colder climates such as much of Vermont, the leaves may get quite a bit of browning from winter injury.  This damaged growth dies back the next season in these climates as new growth emerges.  It will grow to USDA zone 6 in the north (0 to -10 degrees F minimum in winter), and in protected sites in the colder zone 5.

Adam’s needle has been used medicinally and the leaves, with their white curly threads or filaments along the edges, have given rise to the species name.  Native peoples used the strong leaf filaments to weave into fabrics. 

This species of yucca, with its dark green leaves, is native to southeastern states while other species are seen in Mexico and the Southwest.   It has gained popularity with the introduction of several cultivars (cultivated varieties) with variegated leaves.  ‘Color Guard’ has bright yellow centers in leaves, ‘Gold Heart’ has creamy yellow centers, while ‘Bright Edge’ has wide yellow edges to the shorter leaves.  ‘Golden Sword’ also has bright leaf edges, only with larger leaves.  ‘Variegata’ has white leaf edges.

With such striking habit, it lends itself to a specimen in borders.  It is a perfect choice for Mediterranean, Spanish, or contemporary style gardens.  It is a good choice for urban gardens as well, tolerating poor soils, soil compaction, pollution, and winter salt spray from roads.  Give well-drained soil and full sun, although it will tolerate a few hours (3 or 4) per day of shade. Once established, the long tap root makes it quite drought tolerant.  This means too, that you should place it where it will stay as it resents moving.  It is difficult to get all the roots, and those left will resprout to form new plants.  In fact, root cuttings are a main method to propagate this plant.

The other Cary winner for 2012 is the now well-known Knock Out roses.  These have become the top selling roses nationwide as they are relatively hardy, disease resistant, and long blooming.  Knock Out is actually a group of 7 different named selections with flower variations of pink or yellow.  The original introduction, from the year 2000 and the Wisconsin botanist William Radler, has reddish pink and single flowers.  They are reliably hardy to USDA zone 5 (-10 to -20 degrees F minimum in winter).

Although when left unchecked they’ll reach 3 to 4 feet tall and wide, they can be kept shorter with spring pruning.  Pruning to about 12 to 18 inches above the ground in spring may result in more vigor and blooms in warmer areas.  At the minimum, remove dead growth in Spring, crowded stems to allow more air circulation, and about every 3 years remove one third of the older branches.  There is no need to prune off spent flowers (termed “deadheading”) as plants are “self-cleaning”.

As with all roses, give well-drained soil and full sun. Fertilize with a rose fertilizer after each bloom cycle during the season.  Once established, these roses are quite drought tolerant. 

Use Knock Out roses in masses, in borders, or in a row to form a hedge.  They combine well with pinks (Dianthus), daylilies, perennial salvia, ornamental blue fescue grass, and lamb’s ear (Stachys) among other perennials.  For annuals, consider combining them with petunias, sun-loving coleus cultivars, licorice plant (Helichrysum), the silver plectranthus, and spider flower (Cleome) among others. 

Other great trees and shrubs for New England can be found on the Cary Award website (

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