Better Calibrachoas with Growth Control By Jim Barrett

PGR trials on the FloraStar Elite Winners and merit awardees demonstrate the effectiveness of early and late PGR applications.

Have you noticed how popular calibrachoas have become? It isan interesting crop. They can either look very nice or very straggly. Theflowers are small, and unless there are lots of them, the plant does not givemuch of a show. In terms of sensitivity to media pH, calibrachoas are one ofour most demanding crops.

This is a young crop from the stand point of breeding anddevelopment; it was introduced only 10-12 years ago. While numerous companiesare doing calibrachoa breeding, each company’s series is somewhat variable,including varieties with different growth habits and sensitivity tophotoperiod. Note: All calibrachoas are long-day plants. None are day neutral;however, there are big differences in how early in the spring they will flower.

High light and cool temperatures produce much nicer,morecompact plants with a largenumber of flowers, which is one of the reasons they always look so good inthose Pack Trial pictures. Calibrachoas, however, can be very aggressive underthe warmer temperatures of Southern production or early summer temperatures ofthe North and Northeast. The need for lower media pH means that fertilizationwith high ammoniacal nitrogen, such as with a 20-10-20 formulation, is oftenused, which also promotes elongation. In addition, varieties that requirelonger day lengths for flowering can produce long shoots before they aresaleable. We also cause ourselves more aggravation by putting calibrachoas insmaller containers.

The past couple of years, we have grown a large number ofvarieties as part of our photoperiod research and the FloraStar Elite trials(See page 22 for results from the Elite trials). The need to produce moreattractive plants led us to doing growth regulator work for our May field days.For this article, I have chosen the strategy of showing more pictures of theplants and letting them speak for themselves, as in “a picture is worth athousand words.”

There are two important concepts for applying growthregulators to calibrachoas. The first is to achieve early control overelongation, and several methods are available for accomplishing this. Thesecond concept is to use a late drench to produce a more attractive finishedplant and to prevent plants from getting out of control at the end ofproduction and in the garden center. Both concepts are useful for baskets andfor smaller containers.

Early Control

In picture 1, page 70, the plant on the left is a control(no growth regulator) and the one on the right was sprayed with B-Nine at 5,000ppm seven days after planting the rooted cutting. The cuttings were pinched atplanting, and the picture was taken five weeks after planting. The controlplant illustrates the open appearance that can develop when laterals areallowed to elongate too much prior to flowering. For varieties with a trailingor semi-trailing habit, in baskets, this results in all the flowers being outover the edge of the container and the basket not having color on top.

Spraying a growth regulator, such as B-Nine, soon afterplanting is one method for obtaining early control. Another method is to applya growth regulator spray directly to the media at or just after planting. Thisis called a media spray and can be done with any of the chemicals that areactive through the media, A-Rest, Bonzi, Piccolo and Sumagic

An example is Picture 2, above. The plant on the left is acontrol pictured five weeks after planting, with the cutting pinched atplanting. The plant on the right received a media spray; the container wasfilled with media, the media surface was sprayed with Sumagic at 20 ppm and theliner was planted. Because of REI requirements, it is usually easier to plantand spray after the pots have been placed in the greenhouse. We used a sprayvolume of 2 quarts per 100 sq.ft., but some growers will use a volume 2-3 timesthis with lower chemical concentration. This higher volume is often called asprench.

A third method for achieving early control is shown inPicture 3, page 71. The control plant is on the left. The other two plantsreceived a liner dip, where the liner was dipped (root zone only) in a Sumagicsolution and then planted. The concentrations were 1 ppm for the center plantand 2 ppm for the plant on the right. The root ball should be dipped longenough for it to soak up the chemical, which is about 10-30 seconds. This”liner dip” can also be done by drenching the chemical on the trayfrom the top. Liners can be treated 1-4 days prior to planting, which makesthis application method generally easy to accomplish. This technique is alsovery good for reducing the growth of calibrachoas in mixed containers when theyare combined with less vigorous crops, as it is unwise to apply a growthregulator to a combination that might contain slow-growing varieties.

Drench applications

Picture 4, page 70, demonstrates the effects of a latedrench on large baskets. The basket on the right, pictured 11 weeks after plantingreceived a Bonzi drench at 8 ppm seven weeks after planting. There are not moreflowers on the treated basket; it just looks that way because they are pulledcloser together by the reduced shoot length. If the shoots are not elongatingtoo much, the late drench should be applied just before the plants reachsalable size. This will slow growth and keep plants at a salable size longerwithout stopping flowering. The basket on the right is also better for theconsumer since it is not actively growing and does not require watering asfrequently.

Picture 5, left, shows the effect of drench concentration on41/2-inch pots. The liners were pinched at planting, the treatment was appliedat two weeks and the picture is at five weeks. The plants from left to rightare control and Sumagic drench at 1/4, 1/2 and 1.0 ppm. For small containers,the drench usually needs to be applied earlier in the crop than with baskets.Another illustration is of drench concentration is also pictured on the left inPicture 6, where the plant on the right received a Sumagic drench at 1 ppm.Picture 7, left, is an example of a Piccolo drench with the plant on the rightreceiving 4 ppm Piccolo.

These are examples of the benefits of obtaining earlycontrol over the elongation of calibrachoas and for using a drench to keep theplants compact later in the crop. These treatments and rates are examples inFlorida’s relatively warm spring. Growers in the Midwest should start theirtrials at about one-half of these rates, and in the Northwest and New Englandabout one-forth of these rates are good starting points.

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Jim Barrett

Jim Barrett is professor of floriculture at the University of Florida and GPN's consulting editor. He can be reached at [email protected]

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