LSU Agricultural Center….
Ornamental Horticulture E-mail News (April 21st and 28th)

Flower Carpet Roses (from Allen Owings)

Flower Carpet roses from Anthony Tesselaar Plants continues to get some media attention in the south and across the country. The original Flower Carpet roses came out in the 1990s and now there are numerous varieties representing new flower colors (red, white, pink, appleblossom, coral, yellow, scarlet). New for 2008 is Pink Supreme and new for 2009 is Amber. These plants are sold on a very limited basis at a couple garden centers in Louisiana. Flower Carpet roses are usually promoted as “America’s #1 ground cover rose”. Flower carpet roses have performed better in trials in the west, mid west and eastern portions of the United States then they have in the southeast. We are currently deciding at the LSU AgCenter whether to conduct a study looking at performance of the newer varieties to determine if improvements in these plants have been made since their initial introduction.

Mulching Reminders (from Allen Owings)

Spring is a great time to add new mulch to our landscape plantings. All ornamental plants benefit from mulch additions, when done correctly. Good mulching should have several beneficial effects upon plants, soil, and the surrounding area. These benefits include:

• conserving soil moisture
• prevent crusting of the soil surface
• maintain uniformity in soil temperature
• reduce weed seed germination and subsequent growth
• prevents upward splashing of soil fungus
• lessens possibilities of cold damage
• slows erosion
• prevents soil compaction
• adds to the beauty of the landscape

The LSU AgCenter recommends mulching annual bedding plants and herbaceous perennials to a depth of 1”, shrubs to a depth of 2” and trees to a depth of 3-4”. It is important to remember to “go out” with mulch instead of “going up” with mulch. Spread out mulch horizontally instead of piling it up vertically. Recommended mulches include pine straw and pine bark. Many other materials are available also.
 
Excessive mulching around trees continues to be a problem in Louisiana. There are many negative results from over-mulching around trees. One of the tendencies in landscapes now is to make piles of mulch (sometimes resembling the shape of a volcano or fire ant mound) around the base of trees, especially small-flowering trees, such as crape myrtles, in residential landscapes. This creates major problems and is, unfortunately, a practice that is becoming more and more common.

Problems that result from over-mulching and piling mulch around the base of trees include:

-Oxygen starvation of the shallow roots.

-Phloem tissue death (caused by reduced oxygen exchange).

-Increased fungal and bacterial infections (from increased moisture around trunk).

-Heat buildup from mulch decomposition kills stem and trunk tissue.

-Mulches can modify soil pH.

-Microbes in the mulch compete with tree roots for nutrition.

-Accumulated mulch is habitat for rodents that feed on plant tissue.

The Hammond Research Station will be working on mulching studies over the next couple years. Research objectives to be evaluated will be mulching depths, color retention, weed suppression based on mulch type, and other issues.

Landscape Management Short Course (from Allen Owings and Jeff Kuehny)

The LSU AgCenter is cooperating with the Baton Rouge Landscape Association to sponsor a landscape management short course on Tuesday July 15 – Thursday July 17. The majority of the program will be held in Baton Rouge at the Horticulture Hill Farm Teaching Facility on the LSU Campus and at Burden Center. The last morning will be a tour of landscape horticulture research at the Hammond Research Station in Hammond. More details and a final program coming soon.

Vinca (Periwinkle) Information (from Allen Owings and Dan Gill)

One of the most popular summer bedding plants in Louisiana is vinca, also called periwinkle. This annual plants is known for having a very long blooming season. It is also very heat and drought tolerant.
The vinca or periwinkle we use as a bedding plant is Catharanthus roseus. Two other plants used in landscapes, Vinca major and Vinca minor, are related to it and are also commonly known as vinca or periwinkle. Even though they go by the same common names, Vinca major and Vinca minor are different plants all together. They are evergreen, hardy vines that are used as ground covers in shady areas and should not be confused with the bedding plant.
Great improvements have been made in vinca flower color over the past 15 years. In addition, many new series and varieties of these popular plants have debuted.  Vinca flower colors now include pink, deep rose, red, blush, scarlet, white, white with a red eye, lavender blue, peach, apricot, orchid, burgundy and many other shades.
Periwinkles generally grow from 10 to 18 inches tall with a spread of about a foot, although trailing types spread to about two feet.
We do have a problem with vinca in landscape plantings some years. The culprit is a fungus called Phytophthora, and it has always been present in our soils. It is often responsible for root rots and crown rots, and it attacks many types of plants. To avoid disease problems on your vinca, consider the following LSU AgCenter recommendations:
-Select a full-sun location. Vinca need at least six to eight hours of direct sun daily for optimum performance.
–Properly prepare the landscape bed to allow for drainage and aeration. Raise the bed at least 6 inches if drainage is questionable.
–Avoid planting vinca too early – late April through early May is the ideal first planting date for the spring.
–Plant so that the top of the root ball is level with or slightly higher than the soil of the bed. Proper spacing also is important, because a crowded planting limits air circulation and can create conditions more favorable to disease development. Space transplants at least 8 inches apart.
–Mulch to decrease splashing of rainfall and irrigation water from soil to the lower stems and foliage of the plants. Bedding plants should be mulched to a depth of about 1 inch. Pine straw is the preferred mulch material.
–Manage irrigation properly. Vinca need very little irrigation once established. Avoid overhead irrigation.
–Don’t plant periwinkles in the same bed year after year. Rotate them with other summer bedding plants that like sunny locations such as blue daze, dwarf lantana, dwarf pentas, scaevola, verbena, melampodium or sun-tolerant coleus, to name a few.
Some of the varieties of vinca available at retail garden centers include Pacifica, Cooler, and Mediterranean. The Victory series has been introduced in the last ten years and has performed well in Louisiana and Texas trials. The newest vinca are the Titan, Nirvana and Cora series. These all have been very good performers in LSU AgCenter trials at the Hammond Research Station in Hammond and at Burden Center in Baton Rouge. The Titans have the largest flowers of all the vinca groups, while Nirvana and Cora vincas have genetic resistance to diseases.