Perennial Solutions: Campanula carpatica ‘Rapido Blue’ By Paul Pilon

This quick bloomer puts out a tremendous display of color on compact, vigorous plants.

Many growers use one or more types of campanula in their perennials programs. One of the bellflowers commonly produced is Campanula carpatica. Kieft Seed recently introduced an exciting new first- year flowering C. carpatica cultivar named ‘Rapido Blue’.

‘Rapido Blue’ has many desirable attributes, but one of the most notable as its name implies is its quick and early bloom time. ‘Rapido Blue’ blooms up to four weeks earlier than previous cultivars in the species. In addition to its quicker time to flower, ‘Rapido Blue’ has several other desirable attributes. This cultivar demonstrates excellent vigor, great uniformity, good heat tolerance, maintains a compact growth habit and puts on a very showy display of color.

Campanula ‘Rapido Blue’ forms low cushion shaped mounds of small dark green serrated triangular shaped leaves with wavy edges. In the late spring, it develops an abundance of large 11⁄2- to 2-inch upward facing, rich violet-blue flowers. When blooming, this compact perennial reaches only five to seven inches tall and only grows slightly wider than that across. Flowering continues well into the summer.

Campanula carpatica can be grown across most of the country and are hardy in USDA Hardiness Zones 3 to 9. It grows well in locations with rich, moist, but not wet soils. In the North, this is a great candidate for sunny locations, but prefers partial shade in warmer locations. Bellflowers are good for attracting hummingbirds into gardens, but aren’t appealing at all for critters such as dear and rabbits.

In the landscape, this low-growing plant can be an eye-catcher in the front of borders, along paths in rock gardens or used as a showstopper in mass plantings. Its tidy size, yet floriferous nature makes it a great component in mixed containers or ‘Rapido Blue’ can also be used as a showy indoor novelty pot plant. It’s easy to grow and provides great shelf appeal, spurring impulse purchases while it’s blooming.

Propagation

Campanula carpatica ‘Rapido Blue’ can easily be started from seed. It’s recommended to sow four seeds per cell in 288 or larger sized plug trays filled with a well-drained soilless media. Do not cover the seeds after sowing; light is required for germination.

The seed flats should be moistened and moved to a warm environment, where the temperatures can be maintained at 65 to 70o F for germination. Many growers utilize germination chambers during this stage to provide uniform moisture levels and temperatures. Maintain high relative humidity levels (95 percent), soil temperatures between 65 and 72° F, and moisture level 4 until the radicles emerge from the seeds. Germination typically occurs within seven to nine days after sowing.

Following germination, the temperatures can be reduced slightly to 65 to 68° F, the humidity kept at ambient levels and the moisture reduced to between level 3 and level 4. Fertilizers can be applied when the true leaves are beginning to develop, applying 100-ppm nitrogen every irrigation, using a balanced water-soluble source with micronutrients.

To prevent premature flowering, all stages of plug production should occur under short day lengths, preferably less than 13 hours. When grown at the temperatures mentioned above, ‘Rapido Blue’ will reach a transplantable size in approximately nine to ten weeks.

Production

Campanula ‘Rapido Blue’ is ideal for production in small containers; one quart to one gallon sized pots are ideal. Many commercially available growing mixes will work well, provided they provide enough drainage. Plant one plug into the center of small containers; large containers will require multiple liners (two to three plugs into 1-gallon pots) to create fuller appearing plants. Avoid planting the plugs too deeply, they should be planted so the soil line of the plug and the surface media of the container they are being planted into is even. Planting the crown too deeply often leads to crop variability and losses. Many growers opt to apply a broad spectrum fungicide drench after planting.

Bellflowers are light to moderate feeders and perform best when either constant liquid fertilization is applied feeding at rates of 100- to 125-ppm nitrogen or applying higher rates of 200 ppm as needed. Controlled-release fertilizers can also be incorporated into the growing mix using a rate equivalent to 1.0 pounds of elemental nitrogen per cubic yard of growing mix. Maintain a slight acidic pH of 5.8 to 6.2 throughout the production cycle.

Campanula requires average amounts of irrigation. Avoid keeping them consistently wet or overly dry growing conditions. When irrigation is needed, water thoroughly and allow the medium to dry between waterings.

With its compact growing habit, it’s not usually necessary to implement height management strategies when growing campanula ‘Rapido Blue.’ If the plants do require toning, many plant growth regulators are effective at reducing stem elongation on this type of campanula. They are particularly sensitive to applications of paclobutrazol (Bonzi, Paczol or Piccolo) and uniconazole (Concise or Sumagic); application of these products could lead to over-growth regulation if not used judiciously. Consider making one or two spray applications of 2,500-ppm daminozide (B-Nine or Dazide) if height management is necessary.

Insects and Diseases

There are several insect pests and diseases known to be observed on campanula from time to time; however, most of them do not cause significant damage. Growers may find aphids, spider mites, Western flower thrips and whiteflies feeding on them on occasion. The most common diseases which infect bellflowers are Botrytis and crown/root rots caused by the pathogens Pythium and Rhizoctonia. Of these pests and diseases, crown and root rots are the most prevalent and can largely be avoided by planting them at the right depth and maintaining good irrigation practices. Routine scouting can detect these problems early and can be helpful when determining if control measures are required.

Temperature and Scheduling

Campanula carpatica ‘Rapido Blue’ is a great item for mid spring through early summer sales. Flowering plants of this cultivar can be easily achieved when following a few key guidelines.

‘Rapido Blue’ is a first-year flowering perennial and does not require vernalization for flowering. They can be started from seed and will easily and uniformly bloom during the same growing season or produced as a traditional perennial and planted in the summer or fall the year prior to selling them in flower.

The photoperiod or day length has a great influence on flowering and final plant quality. They are obligate long day plants and will easily flower when the day lengths are 14 hours or longer.

In many instances, they will bloom before the containers have filled out (as mentioned above, they’ll even flower in the plug trays). For this reason, it’s very important to maintain day lengths of 13 hours or less during all stages of plug production as well as for the first several weeks of production after they have been transplanted into the final container size. This can be accomplished by most growers by planting them in late March or early April since natural day lengths reach 14 hours in most locations in late April.

If earlier flowering is required, ‘Rapido Blue’ can be planted earlier when the days are naturally short. After they have bulked up for a few weeks long days can be provided using photoperiodic lighting. The most common method of providing long days is to use night interruption lighting (10 p.m. to 2 a.m.) delivering 10 foot-candles of light throughout this period. Once flower buds are visible, growers can remove the lighting and produce them under natural day lengths for the remainder of the crop.

The time to bloom after the onset of long day lengths is a function of temperature. Campanula ‘Rapido Blue’ grown at 68° F as little as eight weeks to flower, while plants grown at 60° F will flower in approximately 12 weeks.

The best quality is achieved when plants are grown in full sun or in greenhouses with high light intensities. Temperatures can also influence the plant’s appearance. The highest quality plants with the largest and most intensely colored blooms are obtained when they are grown at around 60 to 65° F. Cool night temperatures below 50° F will cause the leaves to appear puckered or curled. Production temperatures over 68° F will reduce the overall plant size as well as reduce the size of the flowers.

Availability

Campanula carpatica ‘Rapido Blue’ is brought to the market by Kieft Seed (www.kieftseed.com). To obtain seed, contact your Ball sales representative (www.ballhort.com). Plug flats are widely available and can be obtained through your Ball sales representative or various reputable perennial plug producers.



Paul Pilon

Paul Pilon is a horticultural consultant, owner of Perennial Solutions Consulting (www.perennialsolutions.com) and author of Perennial Solutions: A Grower’s Guide to Perennial Production. He can be reached at 616.366.8588 or paul@perennialsolutions.com.



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