January 2011 Culture, Variety Info

Whetman Pinks Dianthus By Robert Bett and Paul Pilon

Trialed and tested, these healthy dianthus perform well in greenhouses, nurseries and in the landscape.

Dianthus has become one of the most commonly grown perennials in North America. Whetman Pinks, a specialist breeder in the UK, has introduced eight dianthus series offering a broad range of characteristics and grower appeal. Over the years, their introductions have received numerous awards.

To ensure the success of their genetics in the North American market, Whetman selections are put through at least two years of rigorous testing prior to introduction. All selections are initiated at high health laboratories and the onshore cutting source provides virus indexed cuttings, allowing the licensees to distribute top quality and healthy starter materials.

Each series of Whetman Pinks dianthus offers unique characteristics that set themselves apart. Some dianthus were bred to flower early, others were selected by the distinctiveness of the blooms, and other selections were made based on the characteristics of the foliage and plant size.

Whetman Pinks dianthus offers great performance for greenhouses, nurseries and in the landscape. Each cultivar is tested to USDA Hardiness Zone 5. In the landscape, dianthus prefers to be grown in full sun, although locations receiving partial sun are acceptable. Once established, they are fairly tolerant of drought.

Culture

Commercial growers typically produce dianthus in quart 4- to 6-inch containers. They can be grown in peat- or bark-based growing mixes provided there is adequate drainage. Avoid planting dianthus too deeply or crop variability and/or losses from crown rots are likely to occur. To improve or hasten rooting after transplanting, it is beneficial to water the liners just before they are to be planted.

Dianthus requires average to slightly below average amounts of irrigation as they do not tolerate consistently wet or overly dry growing conditions. Maintain the media throughout the production cycle with a pH between 6.0 and 6.5. Nutrients can be delivered using water-soluble fertilizers (75 to 100 ppm constant or 150 to 200 ppm as needed) or incorporating the low rate of an appropriate controlled-release fertilizer.

Many cultivars retain a compact growing habit throughout production and do not require plant growth regulators to control plant size. Some cultivars are more vigorous and other varieties may require some growth control as they approach flowering. Stem elongation can often be reduced by growing them at minimum crop spacing, reducing the humidity levels within enclosed structures, or spacing the containers apart beginning approximately one month before the anticipated market date. One to two foliar applications using the tank mixture of 2,000-ppm daminozide plus 3-ppm uniconazole are effective at controlling stem elongation.

Insects and Disease Control

Aphids, caterpillars, spider mites and thrips may be observed on occasion feeding on dianthus, but rarely become problematic. They are susceptible to Botrytis, crown and root rots (Fusarium, Pythium and Rhizoctonia), leaf spots (Alternaria, Cladosporium, Heterosporium and Phyllosticta) and rust. To prevent the occurrence of these diseases, it is best to manage the environment by providing the proper plant spacing and adequate air movement, controlling the humidity, monitoring the salt levels of the growing mix and providing proper irrigation practices. In most cases, routine scouting is effective at detecting early signs of insect or disease problems; therefore no preventive control strategies are usually necessary.

Scheduling

Flowering of dianthus can easily be achieved from mid spring through mid summer. Choosing the right series of dianthus for the time you need them in bloom is the first step to successfully producing flowering plants. For example, the new Early Birds series is an optimal choice for producing small containers for early sales.

Most cultivars require cold (vernalization) for prolific and uniform flowering; however, some series such as the Early Birds and the Scent First series will flower nicely without cold. When producing large container sizes, it is necessary to provide a bulking phase (eight to 10 weeks) in the late summer/fall prior to being over-wintered. Small containers can be potted in the fall and overwintered or started with vernalized liners in the spring.

After the plants have been vernalized, they will flower under any photoperiod and can be grown with natural day lengths. The time necessary for flowering is largely a function of temperature. Most cultivars will bloom in eight to 10 weeks at 65¡ to 68¡ F following vernalization or 10 to 12 weeks if they are not vernalized. Producing them at cooler temperatures increases the time to flower but improves the overall quality characteristics of the plant, such as the color intensity of the foliage and flowers.