Perennial Solutions: Geranium ‘Rozanne’

May 17, 2005 - 09:52

The best-selling perennial geranium of all time, ‘Rozanne’ is easy to grow and has multiple uses.

Geranium ‘Rozanne’ is a recent introduction, offering many great im-provements over the other cultivars of this genus. ‘Rozanne’, a clump-forming perennial, reaches 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 — approximately 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 plants 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 the 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, also referring to the shape of the seed pods.

‘Rozanne’ is an easy, carefree cultivar with finely cut, slightly marbled, deep-green foliage that turns 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 5-8 and AHS Heat Zones 2-12. It tolerates summer heat best when partial shade and ample moisture are provided. With its vigorous, yet compact habit, and extended bloom time, ‘Rozanne’ is very versatile and well suited for use as a groundcover, border plantings and patio containers.

Propagation

Like many of the new perennial varieties, ‘Rozanne’ is vegetatively produced by means of tissue culture. Tissue culture has allowed this and many other new varieties to reach the market in a relatively short period of time. It is a patented variety; self-propagation is prohibited at this time, as a license is required to commercially propagate this cultivar. Tissue culture laboratories send small plants from tissue culture to several licensed plug producers. These plug producers then grow the plants into various sizes, which are available to commercial growers.

Production

Geranium ‘Rozanne’ performs best when grown in a moist, well-drained medium with a slightly acidic pH of 6.0-6.7. It is a light to moderate feeder and performs best when either a constant liquid fertilization program is used, feeding at rates of 50-100 ppm nitrate, or a controlled-release fertilizer is incorporated at a rate equivalent to 1-11?2 lbs. of nitrogen per yard of growing medium. Geraniums prefer to be kept moist but not consistently wet. Plants grown under drier conditions may struggle but will persist. For plant establishment, it is recommended to maintain average temperatures of at least 65° F. Once plants are established, grow with 55-70° F day temperatures and night temperatures between 55 and 60° F. At these temperatures, 1-gal. containers can be finished from 72-cell plugs in 6-8 weeks. Plants grown at warmer temperatures and low light levels will often become straggly, with reduced quality characteristics.

Even though they can tolerate being produced under high light conditions, it is best to produce geraniums under moderate light levels with a minimum of 3,000-4,000 footcandles. When being grown in greenhouses for early spring sales, ‘Rozanne’ needs relatively low light levels and present additional factors, making optimum conditions for excessive plant stretch to occur. Growers who anticipate this early stretch can evaluate the crop weekly to determine the timing of growth regulator applications. I recommend growers apply foliar applications of Sumagic (Valent USA) at 5 ppm or tank mixes of B-Nine (Crompton Crop Protection) at 2,000 ppm and Sumagic at 3 ppm as needed (please note these are considered Northern rates, adjust them to fit your location). When PGRs are necessary, it usually requires 2-3 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 re-flushed; this step also provides a fuller appearing pot once it has re-grown.

The occurrence of insects is not uncommon but rarely is problematic. Aphids, caterpillars, thrips and whiteflies are the most common insect pests of geraniums. The occurrence of these pests can be observed with weekly scouting, and the appropriate control strategies can be implemented if necessary. The primary diseases of geraniums are fungal leaf spots and root rots. In most cases, the foliar diseases can be prevented or reduced by providing adequate spacing and good air circulation at all times, maintaining a relative humidity Á below 70 percent and, if necessary, using a preventative fungicide spray program. Excessive irrigation, poorly drained growing medium and excessive periods of heavy rainfall could lead to crown or stem rots and ultimately plant loss.

Forcing

‘Rozanne’ is easy to force into bloom any time of the year. It does not have a cold requirement, but I find cold is beneficial to flowering, especially when growing for the early shipments when light levels are naturally low. If cold is provided, 6-10 weeks of exposure to temperatures below 44º F is generally sufficient. The optional cold treatment can occur to either the plug liner or in the final container. ‘Rozanne’ is a day-neutral plant; flowering occurs under any photoperiod, and plants can be forced into bloom under natural day lengths. For the best plant quality, it is recommended to produce this variety under photoperiods of 12 hours or longer, this is when the light levels become optimum for plant and flower development. The time to bloom after transplanting is a function of temperature. It is recommended to force geraniums with temperatures ranging from 60-70º F. ‘Rozanne’ grown at 68º F will take six weeks to reach flowering, while plants grown at 60º F will flower in nine weeks. To optimize plant development and produce high quality plants, I recommend growers force geraniums at 68º F.

Availability

‘Rozanne’ is brought to the marketplace by Blooms of Bressingham. Plug liners are currently available from Yoder Green Leaf and a limited number of licensed plug growers across the country.

About The Author

Paul Pilon is head grower at Sawyer Nursery, Hudsonville, Mich. He can be reached by E-mail at paul@perennial-solutions.com.

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