Perennial Solutions: Viola cornuta Celestial Series By Paul Pilon

Viola brings cheerfulness and nostalgia to any landscape. The Celestial series of viola from Darwin Perennials offers many desirable attributes and was selected for its winter hardiness, heat tolerance, early flowering and compact habit. There are currently five cultivars in the Celestial series: Blue Moon (creamy white flowers lightly washed in sky blue and accented by bright yellow eyes), Midnight (deep, dark, rich violet petals blushed with burgundy with bright yellow eye), Northern Lights (vibrant purple blooms with sunshine yellow and orange blushed faces), Starry Night (mauve purple petals with a brush of primrose yellow in the center) and Twilight (rich combination of mauves and golds).

The Celestial series features first year flowering perennials that produce an abundance of trailing, fragrant blooms atop compact, evergreen foliage. The most prolific flowering occurs in the spring and autumn; however, the Celestial series are ever-blooming and will flower from spring through autumn. The attractive mounds reach 6 to 8 inches in height by 8 to 10 inches at maturity. They perform well across much of the country and are hardy throughout USDA Hardiness Zones 5 to 9. Although this series has been proven to be strong summer performers, placing them in sites with partial shade and adequate irrigation will help to keep them going strong.

In addition to brightening up the landscape, viola are great candidates for use in baskets, mixed containers and patio pots. Consider the strong performance, nostalgia and brightness the Celestial series has to offer.


The Celestial series are vegetatively propagated by using unrooted tip cuttings. Each cultivar is patented; therefore, unlicensed propagation of this series is prohibited.

Unrooted cuttings can be successfully rooted by sticking them directly into a pre-moistened, well-drained growing medium. The use of rooting compounds is not essential, but can slightly reduce the rooting times and increase the rooting percentages. If you elect to use rooting agents, dip the basal ends of the cuttings into a solution of indolebutyric acid (IBA) at rates between 500 to 750 ppm. If possible, the cuttings should be stuck the same day they are received.

Maintain moderate mist frequencies for the first two days of propagation, then provide a low misting regiment until the cuttings have rooted. Over-misting and saturated media will cause the cuttings to lose nutrition and delay rooting. Once roots are present, apply 75- to 100-ppm nitrogen at least once per week. The cuttings usually take approximately three weeks to root with soil temperatures ranging from 68 to 72¡ F. To promote a well-branched finished plant, it is beneficial to pinch the cuttings four weeks after sticking. The liners take approximately five to six weeks from sticking to become fully rooted and ready for transplanting.


The Celestial series is suitable for production in trade gallon or smaller sized containers. They perform best when grown in a moist, well drained medium. When transplanting, the growing medium in the pot should be even with the top of the plug. Planting viola too deeply could lead to stem and crown rot.

Viola requires average amounts of irrigation and does not tolerate overly wet growing conditions. When irrigation is necessary, I recommend watering thoroughly then allowing the soil to dry slightly between waterings. Slight water stress can be used to reduce elongation; however, overly dry conditions often leads to yellowing of the lower leaves.

The highest quality plants can be obtained when growing under moderate to high light intensities (5,000 to 8,000 foot-candles). Low light levels, particularly when combined with over fertilization and consistently moist conditions lead to excessive growth. In the spring, growing them outside in full sun is ideal.

Viola prefer to be grown with light to moderate fertility levels. Nutrients can be delivered using water soluble or controlled release fertilizers. Growers using water-soluble fertilizers apply 100-ppm nitrogen with every irrigation or use 200 ppm as needed. Controlled-release fertilizers are commonly incorporated into the growing medium prior to planting at a rate equivalent to 0.75 to 1.0 pounds of elemental nitrogen per yard of growing medium. Over-fertilizing them causes the plants to grow lush and delays flower development. The pH of the media should be maintained between 5.5 and 5.8 to avoid boron and iron deficiency symptoms as well as to reduce the occurrence of Thielaviopsis.

The Celestial series was selected for their excellent branching habit; however, pinching them once either in propagation or one to two weeks after transplanting will result in fuller plants. They have a compact growing habit and usually do not require height management strategies. Viola responds well to spray applications of 2,500-ppm daminozide (B-Nine and Dazide). Late applications of PGRs may delay flowering and reduce the size of the flowers; therefore, it is best to apply them early in the production cycle. Viola are particularly sensitive to applications of products containing paclobutrazol and uniconazole; use both caution and low rates if you elect to apply these products.

Insects and Diseases

Viola are only susceptible to a handful of insect pests and diseases during production. Aphids, fungus gnats, spider mites, thrips and whitefly are the most prevalent pests growers observe. The primary pathogens growers may experience on occasion are Pythium and Thielaviopsis. Avoiding saturated conditions, high ECs and keeping the pH below 6.0 will go a long way toward preventing these diseases. Other potential and less common pathogens to look for include Botrytis, Cercospora, Colletotrichum and downy mildew. None of these insect pests or diseases require preventative control strategies. Insects and diseases can be detected with routine crop monitoring; control strategies may not be necessary unless the scouting activities indicate actions should be taken.

Temperature and Scheduling

Viola cornuta Celestial series is most commonly grown and marketed in the early spring. They do not require vernalization for flowering. For spring sales, viola can be transplanted in the fall and overwintered or potted in the early spring. Being that viola are day-neutral plants, it is not necessary to provide photoperiodic lighting. The best quality plants are produced when the production temperatures are kept cool. It is recommended to provide 24-hour average temperatures of 55 to 60¡ F by delivering night temperatures of 50 to 55¡ F and 60 to 65¡ F days. At these temperatures, it takes approximately six to eight weeks after transplanting to finish 1-quart sized containers or eight to 10 weeks for 1-gallon sized pots. Don't forget about the opportunity to grow and market the Celestial series in the fall.


The Celestial series is brought to the marketplace by Darwin Plants ( Rooted liners are available from the Ball Horticultural Company ( and several of their perennial propagators.

Perennial Solutions: Viola cornuta Celestial Series

Paul Pilon

Paul Pilon is a horticultural consultant, owner of Perennial Solutions Consulting ( and author of Perennial Solutions: A Grower's Guide to Perennial Production. He can be reached at 616.366.8588 or