Allen Owings, Gordon Holcomb and Anthony Witcher

(Louisiana Agriculture, Winter 2003) The number of annual bedding plant species and varieties available for residential and commercial landscape has increased dramatically in the last five to 10 years. Since 1994, the LSU AgCenter has conducted trials to determine the landscape performance of many warm-season annual bedding plants under Louisiana’s growing conditions. Results provide valuable information for home gardeners, landscape professionals, greenhouse crop producers and retail garden center managers.

Research and demonstration projects are conducted at the LSU AgCenter’s Burden Center in Baton Rouge. Trials are conducted throughout the season using replicated plantings established in raised landscape beds located in full sun. A portion of the trial garden area receives some afternoon filtered shade. Beds are equipped with a micro-irrigation system. Plants are watered as needed, based on species requirements and current environmental conditions. Fertilization, weed control and similar cultural activities are conducted based on recommended practices.

Petunias proliferate

Petunias continue to be popular with many new releases each year. Most of the new petunias are seed-propagated spreading petunias. These include the “Wave” series along with six other petunia series. These petunias reach heights of about 12 inches and, as the name implies, spread about 2-3 feet. Colors available in the “Wave” series, which is the most popular and typically the best performer of the spreading petunias, include purple, pink, misty lilac and rose. In 2002, “Lavender Wave” was added and “Blue Wave” will be introduced in 2003. In LSU AgCenter trials, higher quality ratings for landscape performance have been seen with the rose and misty lilac colors.
 
During the 2000 trial, “Wave” series petunias were found susceptible to sclerotinia blight during January and February. Infected plants were not killed and had outgrown and recovered from the disease by May.

Over the last couple of years, “Tidal Wave” petunias have been introduced. These are classified as hedgiflora petunias. They reach a height of 3 feet with a spread of 3 feet. Colors available in the “Tidal Wave” group are cherry, pink, silver and purple.

Try melampodium

Melampodiums are not a well-known warm-season annual bedding plant but well worth growing based on LSU AgCenter observations. These plants produce yellow or golden daisy-like flowers and do well from late spring into fall. They should be planted in full sun with minimum irrigation for best performance. “Derby” and “Million Gold” are two varieties recommended. A new variety not yet tested at the LSU AgCenter is “Lemon Delight.”

Alternaria leaf spot/blight may be a problem on these plants throughout the summer and fall, but can be controlled with repeated applications of fungicides.

Butterflies love pentas

Pentas are among the best plants for butterfly gardens. For years, the only penta series available was the “New Look” pentas. In LSU AgCenter trials the last two years, “Butterfly” pentas have been the better performers. They do well from late spring through the fall and are vigorous growers and prolific flower producers. No significant disease problems have been observed on the “Butterfly” pentas. They are available in a number of colors including lavender, blush and cherry.

Profusion of zinnias

The new “Profusion” zinnias, also known as landscape zinnias, are available in three colors – white, orange and cherry. All colors have been named All-America Selection winners. “Profusion White” and “Profusion Orange” have also been named Louisiana Select plants because of their superior landscape performance. Powdery mildew and leaf spot diseases that damage many of the traditional cut flower zinnias and bedding plant zinnias do not significantly bother the “Profusion” zinnias.

Another group of zinnias worthy of mention is the narrowleaf zinnias – the most popular of these is “Crystal White.” They are similar in growth habit to the “Profusion” group but have smaller flowers and finer textured foliage.

Spreading begonias

“Dragon Wing Red” and “Dragon Wing Pink” are new begonias. These have different growth habits than landscape begonias. They are more spreading with larger foliage and hold up fairly well in a full-sun landscape planting. These begonias are worthy of increased use in the landscape and would also work well in container plantings.

Vincas come in more colors

Vincas, also referred to as Madagascar or rose periwinkle, are available in more colors and group habits than ever before. Many new flower colors and series are available. The new “Mediterranean” series grows horizontally and reaches only about 8-9 inches tall in a 2-foot spread. It does, unfortunately, seem prone to foliar diseases such as aerial blight during the summer when plants are over-watered or there is significant rainfall.

Other new series of vincas include “Heat Wave,” “First Kiss,” “Victory” and “Sunstorm.” “Victory” along with the older series “Pacifica” and “Cooler” does best in LSU AgCenter trials. For success with vinca, we recommend waiting until May to plant, minimizing irrigation and making sure the soil pH is acidic.

Alternaria leaf spot, which causes defoliation, has become a problem in recent years during September and October on vincas.

In addition to warm-season, annual bedding plant evaluations, trials are conducted on cool-season, annual bedding plants, garden mums, poinsettias, herbaceous perennials, roses and other ornamental plants. These efforts will be enhanced in the next few years with the expansion of nursery and landscape research facilities at the Burden Center.

Allen Owings, Professor, Department of Horticulture; Gordon Holcomb, Professor, Department of Plant Pathology & Crop Physiology; and Anthony Witcher, Research Associate, Burden Center, LSU AgCenter, Baton Rouge, La.

(This article was published in the winter 2003 issue of Louisiana Agriculture.)