Salvia 'Caradonna' is a unique cultivar of the reliable genus and species Salvia nemorosa. The violet-blue flowers are similar to other cultivars of this species except they are held on purple stems that provide an added element of texture. Caradonna reaches 18-30 inches tall, bearing flowers on sturdy stems during the summer months. It was discovered in Uchte, Germany, by Beate Zillmer of Zillmer Pflanzen and is suitable for production in USDA Zones 4-9. In the landscape, it is often used in borders and cut flower gardens where there is full sun to partial shade. The flowers will attract bees, butterflies and birds.
Caradonna is propagated by vegetative tip cuttings in the spring and early summer or by seed any time of the year. Cuttings already in bloom will take longer to root and have a lower survival rate than purely vegetative starting materials. During the summer heat, once the cuttings are in the plug flat, they will often sit for a long time without initiating roots, turn yellow and, many times, plant death will occur. For the most successful vegetative propagation, harvest the cuttings before flowering occurs or produce stock plants under conditions that do not promote flowering. Stock plants should be produced under short-day conditions or with 10-12 hours of light per day. To maintain short-day conditions, it is often necessary to pull black cloth over the crop daily, providing a dark period for a minimum of 12 hours.
It is easy to propagate Caradonna from seed. Germination will occur in about 7-10 days in temperatures of 68-72° F. Placing the plug flats in a germination chamber will most likely improve the germination rate and the time to germinate, but is not necessary to successfully produce this salvia from seed. At seeding, I recommend lightly covering the seed with vermiculite or the same media the plug trays are filled with. It will take 4-6 weeks for the plug to reach a transplantable size.
Salvias perform best in a well-drained media with a pH between 5.8 and 6.2. When providing irrigation, water thoroughly and let plants dry out between waterings. Over-watering often leads to root and crown rots. Salvias are light to moderate feeders, requiring only modest amounts of fertility. Generally, when planting salvias, I incorporate a controlled-release fertilizer into the growing media at a rate equivalent to 3⁄4 pounds of nitrogen per yard of growing medium. Another method to deliver fertility to this crop would be using a constant liquid fertilizer program, delivering 50 parts per million (ppm) nitrate to the crop at each watering.
There are relatively few diseases and insects affecting the production of salvias, and seldom does significant plant injury or losses occur. As mentioned earlier, crown and root rots may occur, especially when grown under wet conditions. I have also seen Botrytis outbreaks in the foliage. Á Usually, the Botrytis is observed in situations in which there is a dense plant canopy, little air movement and water on the leaves for long durations. Aphids, two-spotted spider mites, thrips and whiteflies are the most common insects that may be observed feeding on Caradonna.
Of these insects, the two-spotted spider mite is usually the most cumbersome and difficult to control. Unless regular scouting occurs, the presence of spider mites often goes undetected until significant amounts of plant injury occur. At first glance, the injury to the leaves might be confused with a nutritional deficiency, as from a distance the leaves appear to be turning yellow. Looking more closely, you will observe the damaged leaves are stippled with small, yellowish to silvery-gray speckles. Spider mites are usually found feeding on the undersides of the leaves.
Controlling spider mites is not easy. Because it is difficult to deliver the chemicals to the lower leaf surfaces where they are feeding, there are several life stages present at any time, and they quickly build resistance to pesticides. I have found success by rotating chemical classes at every application, tank-mixing ovicides such as Hexygon and Ovation with adulticides such as Avid and Floramite, and by ensuring good coverage of the sprays to the crop. As always, be sure to follow the chemical labels for rates, application frequency and the total number of applications allowed per crop.
Controlling plant height may be required while producing Caradonna in a container. Before using chemicals to reduce stem elongation, it is usually beneficial to provide adequate space between each plant, which will reduce the competition between plants for light and prevent the plants from growing taller. If chemical plant growth regulators are required, B-Nine has shown the most effectiveness. In the Midwest, I would recommend beginning with an application rate of 2,500 ppm and applying it 2-3 times at weekly intervals. In other locations, it might be necessary to apply the weekly applications beginning with a higher rate. Regardless of location, I have found that it is better to apply lower rates of growth regulators more frequently instead of a single application at a higher rate.
Flowering Caradonna out of season is relatively easy, provided a few guidelines are followed. I recommend cooling (vernalizing) plugs or small containers of salvia for 6-9 weeks at 40° F. The cooling period enhances uniformity and reduces the time it takes to reach flowering. After cooling is achieved, provide photoperiods (day length) of 16 hours by extending the day if necessary, or use a 4-hour night interruption during the middle of the night, providing a minimum of 10 foot-candles of light at plant level. Caradonna is a long-day beneficial plant and will flower best under long days, regardless of the vernalization time. The time plants take to flower depends on the growing temperature after the plants are placed under long-day conditions. Plants grown at 64° F will flower in about eight weeks, while plants grown at 68° F will flower in as little as six weeks.
Caradonna has just recently been introduced to growers in this country and currently may be difficult to locate in the United States. It is listed in the catalogs of Blooming Nursery Inc., Cornelius, Ore.; Sunny Border Ohio, Jefferson, Ohio; and Walters Gardens Inc., Zeeland, Mich. For further availability, contact Darwin Plants, Hillegom, The Netherlands.
This salvia, with its unique purple stem, shines in the landscape and is easy to produce.