Landscape Performance of New Herbaceous Ornamentals

Linda Benedict  |  8/25/2008 8:36:40 PM

Coleus. (Photo by Allen Owings)

Perillas. (Photo by Allen Owings)

Marigolds. (Photo by Allen Owings)

Vincas. (Photo by Allen Owings)

Profusion zinnias. (Photo by Allen Owings)

Ornamental sweet potatoes.(Photo by Allen Owings)

Petunias. (Photo by Allen Owings)

Allen Owings, C. Allen Broyles, Yan Chen, Regina Bracy and Ann Gray

The LSU AgCenter conducts greenhouse and landscape research on many new bedding plants each year to determine production practices to assist growers and observe performance in the landscape to provide garden centers, landscape professionals and home gardeners information on how these plants will perform under Louisiana’s growing conditions. These trials are conducted at the Ornamental and Turfgrass Research and Extension Facility at the Burden Center in Baton Rouge and at the Hammond Research Station in Hammond.

Efforts over the last couple years have evaluated sun coleus, new lantana series, cannas, perennial verbena, vinca, numerous petunias, phlox, daylilies, violas, pansies, African and French marigolds, ornamental sweet potatoes, zinnias, dianthus, garden mums, angelonias and much more. A brief summary of selected results and observations are included in this article.
Ornamental Sweet Potatoes
Ornamental sweet potatoes continue to be popular choices for adding foliage color to the landscape. The newest in this exciting group of plants are the Sweet Caroline varieties. These include the Sweet Caroline and the Sweet Caroline Sweetheart groups. Foliage colors in the Sweet Carolines are green and yellow, red, light green, bronze and purple. Foliage colors in the Sweethearts (heart-shaped leaves) are light green, red and purple. New in the Sweet Caroline ornamental sweet potatoes not found in other sweet potatoes are the red and bronze foliaged varieties and late summer through fall flowering on the Sweet Caroline purple. Another new variety belonging to this group is Bewitched – it has maple-shaped, blackish-purple foliage.

The LSU AgCenter has been evaluating coleus from Proven Winners the past couple years. The best landscape performers include Life Lime, Big Red Judy, Coco Loco, Dappled Apple, Fishnet Stockings, Glennis, Pistachio Nightmare, Merlot, and Twist and Twirl. Most new coleus now are for sun plantings although some of the new coleus, such as Chocolate Mint and the Kong series from PanAmerican Seed, are best for shade plantings. Coleus hybrids from Proven Winners that performed well in south Louisiana landscapes during 2007 were Royal Glissade, Zen Moment and Quarterback.

Petunias being used by landscape professionals and being sold in significant numbers at garden centers are the Waves. This groups of petunias includes the following series – Wave, Easy Wave, Tidal Wave and Shock Wave. All of the varieties in these series have been trialed in LSU AgCenter landscape studies over the last couple years. Colors available in the Wave petunias are purple, pink, rose, lavender, misty lilac and blue. The best performers of these are pink, rose, lavender and misty lilac. Easy Wave colors include blue, coral reef, mystic pink, rosy dawn, red, shell pink, and white. Tidal Waves are available in hot pink, cherry, purple and silver with silver being the best landscape performer followed by hot pink and cherry. Shock Wave is the newest and smallest growing of the Wave petunias. Flower colors are pink shades, ivory, rose, pink vein and purple.

Profusion Zinnias
The Profusion series of zinnias have been around for 10 years, and new color additions are being continually added to the series. Orange, white and cherry were the first three colors of the Profusion zinnias. Profusion Orange has been the best performer of these three. Next came fire and apricot. These have done exceptionally well in AgCenter landscape trials. Profusion Knee High Cherry and Profusion Knee High White are taller growing varieties. New varieties of Profusion zinnias currently being evaluated at the Hammond Research Station are deep apricot, coral pink, double cherry, double fire, double gold and double white.

The newest vincas (also called periwinkle Catharanthus roseus) on the market the last few years have been the Titan, Nirvana and Cora series. The Titan series is seed propagated and produces some of the largest flowers in available vinca varieties. There are eight colors and a mix available in the Titan vinca from PanAmerican Seed. The Nirvana vinca has new DNA engineering that makes it genetically resistant to Phytophthora (root rot, stem rot, aerial bight). It is vegetatively propagated. Nirvana vinca are from Fischer USA and are available in 18 varieties (nine upright, nine cascading) featuring a wide range of colors. The newest vinca series is the seed-propagated Cora series from Goldsmith Seeds. The Cora vincas have the same Phytophthora resistance as the Nirvana series. Titan and Nirvana vincas have been good performers in LSU AgCenter landscape evaluation trials. Evaluation of all varieties in the Cora series is under way at the Hammond Research Station.
For success with vinca in the landscape:

  • Plant in acid soil (pH of 5.0-5.5).
  • Planting location needs to be in full sun.
  • Avoid over-mulching and planting too deep.
  • Plant late April through May after the soil temperature has warmed up.
  • Dramatically limit irrigation.
  • Rotate vinca with other plants in landscape beds.
A popular substitute for coleus are the new perillas. Magilla perilla debuted first followed by Vanilla perilla. The Magilla variety has reddish purple foliage while the Vanilla variety has green and white variegated foliage. While most sun coleus start to flower in late spring to early summer, both of these perillas are very slow to flower in the landscape – first flower is in October. This late flowering eliminates the need to dead-head. Perillas are great foliage plants for a full sun landscape.

Moonstruck is the newest variety in the African group of marigolds. They have performed equally to other established varieties, such as the Incas and Antiguas. The Safari and Durango series of French marigolds have been favorable performers in landscape trials in 2006 and 2007.

Allen Owings, Professor, Hammond Research Station; C. Allen Broyles, Research Associate, Burden Center, Baton Rouge, La.; Yan Chen, Assistant Professor, Hammond Research Station; Regina Bracy, Professor, Hammond Research Station, Hammond, La.; and Ann Gray, Instructor, Southeastern Louisiana University, Hammond, La.

(This article was published in the summer 2008 issue of Louisiana Agriculture.)

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