September's Flower of the Month

Joseph's Coat 

 (Alternanthera dentata ‘Purple Knight’)

A few weeks ago Amiable Spouse and I took six-year-old granddaughter Emily to the mall. We wanted to ride the carousel and run a few errands while we were out.

We were progressing through our itinerary quite well until Emily found the three-way mirrors just outside the women’s dressing room. We watched and laughed as she twisted and turned, struck poses, danced, and admired herself in the mirrors. We had to entice her away by promising to go directly to the ice cream parlor. 

I know just how she felt. Recently I was privileged to visit the trial gardens at the University of Florida in Gainesville. Lined up like soldiers were rows and rows of foliage and blooming landscape plants. I was like Emily in front of the three-way mirrors. I couldn’t get enough of what I was seeing. I took hundreds of pictures and made mental notes of some of the plants that I wanted to try in my garden at home. 

I felt that I had found an old friend when I saw Alternanthera ‘Purple Knight’. I grew it in my garden last year, and after being killed to the ground by winter’s cold, it re-emerged this year for an even better show. ‘Purple Knight’ is a tropical perennial, so its return this year was probably due to the fact that our winter was very mild. I took cuttings before the first frost to be sure that I didn’t lose it during the winter.

The bright purple foliage of this plant is particularly useful in the garden. Like the basic black dress in every lady’s wardrobe, it combines with everything. Next to yellows and oranges, all of the colors pop. A handsome contrast of colors is evident when purple is displayed next to white or silver—or red –or chartreuse, for that matter. I can think of no color that does not work well with ‘Purple Knight’.

In the Garden

I can envision it rising behind a sea of ‘Margarita’ sweet potato. The dark purple and chartreuse colors would contrast beautifully. It would pair beautifully with any silver-leaved plant, such as dusty miller. I am itching to combine it with one of the sun coleuses that have chartreuse leaves and the same purple contained in the Alternanthera. I have it in a container garden where I paired it with Lamium ‘Beacon Silver’, and in another place in the landscape where it adds a splash of color to some sun-tolerant white caladiums. So many beautiful combinations are possible, but, alas, time and garden space are both limited.

In a friend’s garden, it backs a planting of ‘Gold Mound’ lantana. The contrasting bright yellow of the lantana contrasts beautifully with the dark purple of the Alternanthera, and the two-foot tall rounded shapes of Alternanthera complement the flat, spreading form of the lantana that spills about its feet. In another garden, it is planted in front of a group of tall lemongrass. The spiky form and bright green of the lemongrass contrast beautifully with the mounding ‘Purple Knight’. 

Kinds

‘Purple Knight’ is a cultivar of the species Alternanthera dentata. From the same genus comes the species Alternanthera fiocoidea which offers many additional choices to today’s gardeners. Among the most popular are ‘Aurea’, which has multicolored leaves; ‘Partytime’ with brilliant cerise blotches on the leaves; ‘Snow Queen’ which has green leaves with striking white edges which may turn pink in cool weather; ‘Chartreuse’  which is a low-growing cultivar with bright yellow-green leaves; and ‘Tricolor’, which sports larger leaves with purple and pink variegation.  

Many other species of Alternanthera exist. Some are invasive weeds such as A. philoxeriodes, or alligator weed that is usually found growing in water, and A. pungens, or Khaki weed found growing in Hawaii and other places. A popular aquarium plant is A. reineckii. However, only two of the species are of interest to gardeners; Alternanthera ficoidea, known by the common name of Joseph’s coat, and A. dentata, from which ‘Purple Knight’ was selected. 

Look for ‘Purple Knight’ at your favorite garden center. Plant it in full sun to partial shade in a bed improved by the addition of organic matter, if needed. Light applications of slow-release fertilizer will keep it growing vigorously. If it grows taller than you want it to, simply prune just above a set of leaves. It will branch and continue to grow, and never miss a beat when the dog days of summer drive you inside.

Click here for a list of plants in the archives.