Taming the Wild Calibrachoa

July 9, 2002 - 07:19

The crop that consumers love and growers love to hate. New research from the University of Florida might just change your perspective on floriculture’s newest “wild child.”

Eye-catching color and vigorous growth have brought nothing
but popularity for Calibrachoa, and it has become one of the industry’s
hottest vegetatively propagated specialty annuals. Calibrachoa’s petite,
single, petunia-like flowers, finely textured foliage and trailing growth habit
make it an ideal plant for hanging baskets either alone or in mixed plantings.

As with many vegetatively propagated items, producing
Calibrachoa hanging baskets does not come without challenges. Taming vigorous
growth to produce a more attractive basket, facilitate shipping and keep plants
untangled in a high-density growing situation are concerns. At the University
of Florida, we have evaluated the use of growth regulator drench applications
to slow the growth of Calibrachoa, which should make this high-value crop more
appealing to growers.


In the spring of 2000, ‘Mini-Famous Pink’ and
‘Mini-Famous Blue’ Calibrachoas were grown in 10-inch baskets with
five plugs per pot and were fertilized every watering with 150 ppm of 20-10-20
fertilizer. The planting date was February 23. Four weeks after planting, three
Bonzi rates were applied as a drench using 15 fluid ounces of solution per
container. At the time of treatment, plant size (average of plant width and
length of shoots below container rim) was measured at 14.5 inches for Pink and
14 inches for Blue, as indicated by the line in Figures 1 and 2, page 10.
Plants of this size will make good, salable plants, and a grower would want to
slow the growth rate at this point to keep the plants from becoming overgrown.

Mini-Famous Blue appears to be somewhat more vigorous than
Mini-Famous Pink and less sensitive to Bonzi, which indicates the variation in
vigor that occurs with different Calibrachoa varieties. In addition, this trial
demonstrated that both varieties showed favorable responses to the Bonzi drench
treatments. An application of 1 ppm Bonzi reduced the final plant size by 15
percent for Pink and 12 percent for Blue when plants were measured five weeks
after treatment. The high rate of 8 ppm reduced plant size by 28 percent for
Pink and 27 percent for Blue, as compared to the control plants. Note the line
in the figures that indicates the size of the baskets at treatment and that the
8-ppm Bonzi drench slowed, but did not stop, growth. After the 8-ppm drench,
the Pink Calibrachoa baskets grew 2.5 inches, and the Blue variety grew six
inches (see Figures 1 and 2, page 10).

Taking these varietal differences into account, we carried
out a similar Á trial in spring 2002 with ‘Mini-Famous Rose
Pink’, ‘Mini-Famous Light Blue’ and ‘Mini-Famous
Yellow’. For this trial, the 10-inch baskets were planted on February 19
and fertilized every watering with 300 ppm 15-5-15 fertilizer. The plants were
treated April 11 (seven weeks after plant date), and the accompanying pictures
were taken on May 18, 2002. With regard to the Rose Pink and Light Blue
varieties, results were very similar to the 2000 trial. As can be seen in the
pictures, Mini-Famous Yellow was the most vigorous of the three varieties in
the 2002 evaluation. For the Yellow, 16 ppm Bonzi was required to provide the
same degree of control as the 2 and 4 ppm used on Rose Pink and Light Blue.

Influencing Factors

Bonzi is a helpful tool when trying to control Calibrachoa
growth in production, as illustrated in this study. Differing cultural
situations require adjusted rates according to growing temperature, fertilizer
applications, time of year (light intensities and day length) and production
spacing. Growers in the North, who produce Calibrachoa early in the spring,
should be careful not to overapply Bonzi. The lower temperatures and lower
light levels make plants grow much slower, requiring lower Bonzi rates as
compared to the Southern-grown plants in our study.

Due to the large degree of variation in Calibrachoa
varieties, even within a series, growers should assess how vigorous each
variety is within a series to determine the optimum growth regulator rates.
Several breeding companies are actively working to improve their lines of
Calibrachoas, which will result in the rapid introduction of new varieties and
changes to existing varieties. So, growers need to keep up with these changes
to know the growth habits of the varieties being used.

Calibrachoas flower faster under long days. Baskets started
early and without lights will produce more vegetative growth, thus potentially
requiring more growth regulator than lit plants. Some liner producers initiate
flower buds by lighting the cuttings while they are rooting, which can greatly
reduce the time to flower in the finished container and may reduce the amount
of growth regulator needed.

Timing the drench applications depends on how the baskets
are produced. In these studies, we applied the drench late, after the baskets
were at salable size. This may be a good strategy for growers producing plants
for a market where larger baskets are needed. A grower that produces baskets on
the bench or one that hangs baskets close together may want to keep the baskets
more compact by applying Bonzi earlier, which prevents the plants from growing
together and makes shipping easier.

These studies demonstrate the benefit of using a late Bonzi
drench at rates of 1-16 ppm to control Calibrachoa baskets. Sumagic could also
be used for this late drench, but we have not evaluated optimum rates. Another
strategy some growers might prefer is to control early growth with growth
regulator sprays applied while the plants are still vegetative. Then finish the
baskets with a late drench to hold them at the desired size longer. Depending
on a grower’s individual situation and preferences, there are several
chemical options for the spray applications, including B-Nine; Bonzi; Sumagic;
a tank mix of B-Nine and Cycocel; and a tank mix of B-Nine and A-Rest. style="mso-spacerun: yes"> 

About The Author

Erika Berghauer is a graduate student, Jim Barrett is professor of floriculture and Rick Schoellhorn is associate professor of floriculture at the University of Florida, Gainesville, Fla. They can be reached by phone at (352) 392-1831 or E-mail at rksch@mail.ifas.ufl.edu.

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