December 2001

Success With Campanulas By John Dole, Todd Cavins and Theresa Bosma

Tall, open spikes of bell-shaped flowers mark thedistinctive cut flower ‘Canterbury Bells’, or Campanula medium. TheChampion series sports 1- to 1 1/2-inch-long, upward-facing flowers in fourcolors: Blue (actually purple), Pink (nice, clear pink), Light Blue (slightlypaler purple than Blue) and Lavender (beautiful white with a purple cast).While some growers have had much success growing Champion in the field, itgenerally produces the tallest stems, at 24-30 inches, in the greenhouse.Striking and different, this species is rapidly becoming a popular cut flower.

Campanula medium has been grown for many years, but oldercultivars were biennials requiring a lengthy cultivation time and cold or shortdays followed by long days for flowering. The lengthy flowering requirementsmade the crop unacceptable for large-scale greenhouse cut flower production.However, the cultivar series Champion now offers a production time of 18-23weeks in the greenhouse with no cold requirement for flower development.

Propagation

Campanula is seed-propagated and works well when grown inplugs. During stage one, the seed should be germinated at 65-68° F, with aconstant 68° F for four days after sowing providing the best results.Seedlings should germinate in 5-10 days. During stage two, after seeds germinate,apply 100 ppm nitrogen from a complete fertilizer and grow at 68-72° F.During stage three, when plants are filling out the plug tray, a media EC of0.7-1.0 dS/m (2:1 dilution) or 1.0-1.5 dS/m (pourthru) should be maintainedusing a complete fertilizer. Sakata recommends using calcium nitrate at thisstage. The seedlings are ready to transplant from the plug flat in stage fouras they have 2-3 true leaves. Do not allow plugs to become root-bound andovergrown as they will stunt and not produce long stems after transplanting.Also, seedling Campanula plugs are especially susceptible to root and crownrots and should be handled accordingly. Á

Flowering Control

When Champion was first grown in the United States someproducers obtained long, strong stems while others had short plants thatflowered quickly. The problem appeared to be photoperiod; we initiatedexperiments to determine the photoperiod and light intensity requirements ofCampanula Champion. We germinated Champion Blue and Champion Pink seeds in 8- or16-hour initial photoperiods; transplanted the seedlings when 2-3, 5-6 or 8-9true leaves developed, and placed them under 8-, 12- or 16-hour finalphotoperiods.

The lowest flowering percentage for Champion Blue (less than1 percent) and Champion Pink (16 percent) resulted from plants grown in the8-hour photoperiod continuously (see Figure 1 below). One hundred percentflowering occurred when Campanula were grown in the 16-hour final photoperiod,indicating that Champion Blue and Champion Pink are long-day plants. Plantsgrown initially in the 8-hour and finished in the 16-hour photoperiod had thelongest commercially acceptable stems (see Figure 2, page 32). Plants needed todevelop 8-9 leaves before all plants flowered, indicating that Campanula Championhas a juvenile phase, a period of vegetative growth before plants can produceflowers. Stem diameter was generally thickest for plants grown in the 8-hour,compared to the 16-hour, initial photoperiod. However, the 8-hour initialphotoperiod delayed flowering compared to the 16-hour initial Áphotoperiod (see Figure 3 above). Plants receiving high-intensity discharge(HID) supplemental lighting during the 16-hour initial photoperiod flowered 11days quicker compared to plants not receiving HID supplemental lighting. Wealso calculated profitability for each treatment and the highest profits wereobtained from campanula grown in the 8-hour initial photoperiod and transferredat 8-9 true leaves into the 16-hour final photoperiod.

According to Harold Wilkins, the original species C. medium,Canterbury Bells, a popular garden biennial, has a complex but remarkableenvironmental sequence. Flowers are initiated only after vernalization undershort days (SD) followed by long days (LD). Only older seedlings perceive thecold and SD signals. Stem elongation occurs without flowering when plants aretreated with gibberellic acid (GA3) under SD. If these elongated plants arecold-treated, they flower under LD at the same time as the vernalized plantsgrown under SD and subsequently placed under LD.

Temperature.Germinate seed at 60-70° F. Grow at 55-65° F nights during production.Plants for field cut production can tolerate light frosts. According to BetsyHitt of Peregrine Farm, temperatures down to 20° F have not causedproblems. Plants may be able to take lower temperatures. Campanula areparticularly suited to unheated greenhouse production, which encourages long,thick stems and provides protection from weather. In areas of mild winters,plants can be field-planted in the fall and overwintered for early springflowering.

Light. Plants shouldbe forced under high natural light or HID if natural light levels are low.Supple-mental HID lighting is used in northern Europe. Long days can beprovided by incandescent mum lights illuminated from 10 p.m.-2 a.m.

Water. As with mostspecies of campanula, plants should not be overwatered and should be grown onthe dry side. On the other hand, campanula is one of the first species to wiltand may require frequent irrigation. Wilting should be prevented as it cancause crooked stems.

Nutrition. Campanulaare moderate feeders. We have grown plants in containers using 250 ppm nitrogenfrom 20-10-20, but lower rates should be used with bed production due to lessleaching. A medium EC of 0.7-1.0dS/m (1:2 dilution) or 1.0-1.5 dS/m (pourthru) should be maintained. Sakatarecommends using a calcium nitrate-based fertilizer. Sakata also reports thatboron deficiency will induce distortion and tip abortion and iron deficiencywill cause leaf tip burn.

Media. Anywell-drained medium with a pH of 6.0-7.0 can be used.

Spacing and Pinching.Plants should be spaced 4-6 inches apart for single stem production and 10-12inches apart for pinched production. The longest stems are produced withsingle-stem production, which is best for greenhouse production. Pinchedproduction works best for field or unheated greenhouse production; 6-10 stemscan be harvested per plant.

Support. Netting ishelpful as stems are weak at the base, especially during low-light periods.Netting is highly recommended for outdoor production because the cup-shapedflowers fill with water and fall over.

Schedule/Timing.Production time varies from 18-23 weeks, with prompt transplanting andapplication of long days and warm production temperatures producing theshortest crop times (Table 1). Plants can be grown in ground beds, 1-gallonpots or 2-inch-deep flats. The longest stems will be obtained with ground bedsand pots.

Insects. Plants aresusceptible to thrips, aphids, spider mites and fungus gnats. Thrips areespecially prevalent and can be particularly damaging to dark purple flowers.Fungus gnats are typically a problem during propagation.

Diseases. Campanulahas problems with Botrytis, which can spot or blight the large flowers. Flowerspotting can be especially prevalent on field-grown campanula. Root and stemrot (Fusarium species, Rhizoctonia solanii and Sclerotinia sclerotiorum) can bea major problem during production, especially from germination until plants arehalf-grown. Also possible are powdery mildew, aster yellows and a number ofleaf spot diseases; the latter two diseases would be rare in the greenhouse.

Postharvest. Stemsshould be harvested when 2-3 lower flowers have opened. They will respond bestto being placed in 100° F warm water immediately after harvest followed bya 24-hour, 5-percent sucrose pulse. Fresh cut, unstored flowers will have avase life of 10-14 days. Cut stems can be stored at 35.5° F for one week inwater or dry with little shortening of postharvest life; as with most species,however, storage in water provides the best results. Longer storage of up tothree weeks in water or up to two weeks dry will result in a shorter vase lifeof 6-9 days. Although not tested, lower storage temperatures are recommended asflowers continued to open even during cold storage. Dry storage will probablybe more effective at temperatures close to 32° F. In the arrangement orbouquet, continuous 1.0 percent or 2.0 percent sucrose solution works well. Thestems take up much water and as such perform best with no foam in the vase.Buds continue to open after harvest.

Flowers are sensitive to ethylene, which causes browning andshriveling of open petals; buds may also discolor and die. Ethylbloc (1-MCP)and silver thiosulfate (STS) are effective at preventing ethylene damage.

Summary

The key points for successful Campanula Champion productionare to grow them initially under 8-hour short days to enhance vegetative growthand transfer them at 8-9 true leaves into 16-hour long days for flowering.Too-short plants will result from plugs becoming root-bound and from long daysbeing applied prematurely. Plants are susceptible to root and crown rot,especially in the plug stage. Watch the watering, as underwatering-inducedwilting will cause crooked stems and overwatering will promote rots. Finally,enjoy the striking beauty of a well-grown campanula cut flower.

This research was supported in part by Sakata Seed. Wethank Vicki Stamback, Bear Creek Farm, for providing marketing information andLeah Aufill for production assistance.