Editors’ note: Each January, ‘Perennial Solutions’ features the Perennial Plant Association’s (PPA) Plant of the Year, and this year is no different. This year, the PPA has selected one of Paul Pilon’s past feature plants as its 2008 Plant of the Year. Geranium ‘Rozanne’ was first featured in the May 2005 issue, and the author has updated the original with new information for the current year.
With its ease of production, desirable attributes and garden performance, geranium ‘Rozanne’ was recently named the 2008 Plant of the Year by the Perennial Plant Association (www.perennial  plant.org). ‘Rozanne’ is a clump-forming perennial, reaching 20 inches tall and 24 inches wide. Its large five-petaled, saucer-shaped, violet-blue flowers with white centers are larger than most other geranium cultivars, about 21⁄2 inches in diameter. This cultivar has great heat tolerance, allowing it to bloom for extended periods in much of the country. In many climates, it is a continuous bloomer, flowering from late spring to early fall. In the southern states, it blooms from late spring to early summer; reblooming may occur in the late summer when they are trimmed back after the initial flush.
‘Rozanne’ is a naturally occurring hybrid of Geranium himalayense and Geranium wallichianum ‘Buxton’s Variety’. It was discovered in 1990 in the garden of Donald and Rozanne Waterer of Somerset, England. The Greeks first named geranium ‘Geranion’ from the word ‘geranos,’ which translates to crane, referring to the long beak of the seed pod. Today, geraniums are commonly called Cranesbill.
‘Rozanne’ is an easy, carefree cultivar with finely cut, slightly marbled deep-green foliage, turning reddish brown in the autumn for added interest. Cranesbill can be grown in average to moist soils in locations with partial to full sun throughout USDA Hardiness Zones 4-8 and AHS Heat Zones 12-2. They tolerate summer heat best when partial shade and ample moisture are provided. With its vigorous yet compact habit and extended bloom time, ‘Rozanne’ is a versatile flower that’s well suited for use as a groundcover, border planting or patio container.
‘Rozanne’ is vegetatively propagated by means of tissue culture. It is a patented cultivar; self-propagation is prohibited at this time, as a license is required to commercially propagate this variety. Tissue culture laboratories send small plants to several licensed plug growers who produce them in various sizes for the industry.
Geranium ‘Rozanne’ is well suited for production in 1-gallon containers. Transplant one liner per container; the top of the starter plug should be even with the soil line of the finished container. They perform best when grown in a moist, well-drained growing mix. Many commercially available peat- or bark-based growing mixes work well, provided there is good water-holding ability and adequate drainage. Irrigate as needed when the plants are young and becoming established. Once the plants are large, they will dry out more quickly and require more frequent irrigations. Overall, it is best to grow them slightly moist and never allow them to wilt. When irrigation is needed, water them thoroughly, ensuring the entire growing medium is wet or nearly saturated.
Geraniums are light to moderate feeders and perform best when the pH is kept between 5.8 and 6.4. To avoid excessive stretching, growers should maintain lean nutritional programs. Growers using water-soluble fertilizers commonly apply 50- to 100-ppm nitrogen with every irrigation or use 150-200 ppm as needed. Controlled-release fertilizers are commonly incorporated into the growing medium prior to planting at a rate equivalent to 111⁄2 pounds of elemental nitrogen per yard of growing medium. Plants grown under high fertility regimens generally become very lush (leggy) and may take longer for them to flower.
For plant establishment, it is recommended to maintain average temperatures of at least 65° F. Once they are established, grow geraniums with 55-70° F day temperatures and night temperatures at 55-60° F. At these temperatures, 1-gallon containers can be finished from 72-cell plugs in six to eight weeks. Plants grown at warmer temperatures and low light levels will often become straggly with reduced quality characteristics. The best-quality plants are produced under moderate light levels with a minimum of 3,000-4,000 foot-candles.
Controlling plant height may be necessary when producing plants for early spring sales, when the natural light levels are low or when being produced at high plant densities. Growth regulators are most effective if they are applied just as the plants are beginning to elongate rapidly. I recommend growers apply foliar applications of uniconazole at 5 ppm or tank mixing daminozide at 2,000 ppm with uniconazole at 3 ppm as needed. These are northern rates and may need to be adjusted to your growing conditions. When PGRs are necessary, it usually requires two to three applications at seven-day intervals to provide adequate height control. If excessive growth has occurred, geraniums can be trimmed to 3 inches above the container and reflushed; this step also provides a fuller appearing pot once they have regrown.
The occurrence of insects is not uncommon, but it’s rarely problematic. Aphids, caterpillars, fungus gnats, shore flies, thrips and whiteflies are the most common geranium pests. The primary diseases of geraniums are fungal leaf spots and root rots. In most cases, foliar diseases can be prevented or reduced by providing adequate spacing and good air circulation at all times, maintaining a relative humidity below 70 percent, and watering early in the day to allow the foliage time to dry. Excessive irrigation, poorly drained growing medium and excessive periods of heavy rainfall could lead to crown or stem rots and, ultimately, plant loss. 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.
Geranium ‘Rozanne’ can easily be scheduled to produce blooming plants any time of the year. They do not have a cold requirement for flowering, and growers can confidently use either vernalized or unvernalized starter materials. However, cold treatments can safely be provided to either the starter materials or to plants in the final container sizes. ‘Rozanne’ can be produced at natural photoperiods, as they are day-neutral plants that will bloom under either short- or long-day conditions. For the best plant quality, produce this variety under photoperiods of 12 hours or longer, when light levels are optimum for plant and flower development. The time to bloom after transplanting is primarily a function of temperature. When grown at 68° F, ‘Rozanne’ will take about six weeks to reach flowering, while plants grown at 60° F will flower in nine weeks. To optimize plant development and produce high quality plants, I recommend growers force geraniums at 68° F.
Geranium ‘Rozanne’ is brought to the marketplace by Blooms of Bressingham. Plug liners are currently available from Yoder Brothers, Inc. (www.green-leaf-ent.com ) and a limited number of licensed plug growers across the country.