N.C. Flower Growers' Bulletin - February and April, 2002 Volume 47, Numbers 1 & 2

Success with Vegetative Petunias andCalibrachoa

John M. Dole, Brian E. Whipker and Paul V. NelsonDepartment of Horticultural Science

Two ofthe most outstanding vegetatively-propagatedbedding plants are petunias and calibrachoa. Thesetwo closely-related species offer consumers rapidgrowth, a wide range of colors and durability. Thevigor of petunias and calibrachoa are great forconsumers, but present a challenge to growers - toomuch ofa good thing can make for tangled plants andshipping problems. In the following article we willdiscuss how to cost-effectively grow petunias andcalibrachoas with an emphasis on the areas we havebeen researching: propagation and growth (vine)control.

Cultivars

Most vegetatively-propagated petunias arc hybridsbetween the bedding petunia (Petuniaxhybrida) andPetunia axillaris. The original seed-propagatedbedding petunia is a hybrid between P. axillaris andP. intergrifolia.However. the

reintroduction of P.

axillaris geneticsbrought a greateremphasis on vigorous,trailing growth andpostproductiondurability. The first newcultivar released in the

early 1990's wasS u pert u n i a s ' M.Supertunias™ arevegetatively-propagated, because thisgroup produces few ifany seed. The seed-propagated 'Wave' serieswas also introduced and

has similar characteristics, but a more restricted color

range. A proliferation of new cultivars have expandedthe range of growth habits, colors, and degree ofdoubleness being offered.

The calibrachoa (Calibrachoa hybrids) is considereda new species in the floriculture trade, but actually hasbeen in cultivation since the early 19th Century. Arenewed focus on the Calibrachoa genus has resultedin the introduction of several new cultivar series.

Calibrachoa have a more limited color range thanpetunias, but finer textured foliage, more pronouncedtrailing habit, and abundant small, single flowers.

PropagationHID lighting improves rooting during low light timesof the year, especially for slow rooting cultivars suchas Cascadia Charme and will reduce time to

transplanting by 7 to 10days. Cultivars which normallyroot rapidly will be ready to transplant in 10 to 14days, slow rooting cultivars without HID lighting willbe ready to transplant in 17 to 24 days. Either metalhalide or high pressure sodium lighting can be used.

Growing plugs underHID lighting and shortdays will result inshorter plants. Usingambient lighting andlong days will increaseplug height and finalplant height for somecultivars. Long dayphotoperiods canincrease plug height andfinal plant height forsome cultivars and

decreased final plantdiameter for all

cultivars.

Cuttings should berooted at 7()"F minimum

temperature with bottom heat. Use propagation tentsand avoid overmisting which slows rooting andincreases the likelihood of Botrytis and bacterialdiseases. Some propagators recommend using rooting ^

N.C. Flower Growers' Builei in - February and April, 2002 Volume 47, Numbers I & 2

hormones with 2500 IBA, especially on slow to rootcultivars such as Cascadia Charme. Using 105 plugflats allows for betterair circulation and results in less

disease problems as compared to the higher density288 plug Hats.

Flowering ControlThe typical seed-propagated petunia are facultativelong day plants. Flowering will occur under LD orSD; however, plants will flower earlier with longer

photoperiods and higher light intensities. Mostvegetative petunias are also facultative long day plants:however, a few cultivars act as short day or dayneutral plants. Apparently high light intensity canovercome photoperiodism as some cultivars are longday plants under ambient light, but are day neutralunder HID lighting. Calibrachoas are thought to befacultative long day plants.

What does this mean for the grower? Long daylighting should be given to both plugs duringpropagation and finished plants during the short daytime of the year, from October to March to decreasetime to flowering. Long day lighting applied onlyduring propagation may decrease crop time forphotoperiod-responsive cultivars. such as PetituniaBright Dream, by up to two weeks. Generally,however, long day lighting during propagation willdecrease crop time by a week or less.

TemperatureGrow at 60 to 65°F night temperature until rooted

cuttings or plugs arc established in the final container.Continue growing petunias at 60 to 65"F nights and 60to75°Fdays for most rapid growth: lower temperaturesof 55 to 60°F can be used, but will slow growth.Calibrachoa can be grown at a wider temperaturerange from 50"F night to 85"F day.

LightGrow plants under a minimum of 5.000 to 6,000footcandles. HID lighting of 500 footcandles or moreimproves rooting during low light periods, especiallyfor slow to root cultivars. HID lighting can alsoincreased number of branches, but only for plantsgrown under long days.

IrrigationWhile petunias and calibrachoas are drought tolerant

in the landscape, keep plants moist during productionfor optimum growth and to avoid lower leaf loss.

Nutrition

Both petunia and calibrachoa are considered to berelatively heavy feeders with recommended ratesfrom suppliers of 250 to 350 ppm N for petunia and200 to 300 ppm N for calibrachoa. However, wefound that 150 ppm N was sufficient for good growth.Higher fertilizer rates either had no effect or delayedflowering. Not surprisingly, however, foliage colorwas darker green for plants irrigated with 300 ppm N(Figure 1). If lower fertilizer rates near 150 ppm Nare used, plants can be greened up by using higherrates for a couple of weeks just prior to shipping.Phosphorus rates should be 1/4 to 1/3 of nitrogen andpotassium rates should be 2/3 of nitrogen. So afertilizer like 13-2-13 or 15-5-15 Cal-Mag wouldwork well. Calibrachoa and petunias have a highrequirement for iron: be sure to incorporate additionaliron into the nutritional program. Iron chelates can beused as sprays or drenches.

Growing SubstratePetunia and calibrachoa are adaptable plants whichthrive in a variety of commercial growing substrate.pH should be monitored and maintained between 5.5to 6.0. Calibrachoa can tolerate pH's slightly lowerthan 5.5.

Growth Control

Both petunias and calibrachoa grow rapidly and canbecome leggy. Environmental manipulation is thefirst control strategy to consider. Grow plants under

Figure 1. Petunia Pocket grown at four differentnitrogen rales from 20-10-20 (front left to front right:0. 150, 300, and 450 ppm N). Note color differencein flowers and foliage due to fertilizer rate. ^.

N.C. Flower Growers' Builei in - February and April, 2002

high light, cool temperatures, and zero to negativeDIF to reduce stretch and promote rapid flowering.Pinching and pruning can also be used as needed tocontrol growth, see Pinching section for details.

Many vegetative petunia cultivars are particularlyvigorous and plant growth regulator (PGR)applications may be required. Based on research atNorth Carolina State University, the followingchemicals and rates are recommended for vigorousvegetative petunia cultivars. when applied 2 weeksafter transplanting the cuttings into 6-inch pots.Growers should use the following rates as beginningguidelines and make adjusts to customize rates fortheir operation.

A single A-Rest• spray at 80 ppm was effective. Theresidual effects of A-Rest" appear to wear off afterabout 50 days and this suggests that a secondapplication at a lower rate may be beneficial. Sumagic"foliar spray rates between 20 to 30 ppm were effective,with the higher rate providing more control. Bonzi®also worked well on vegetative petunia and foliarspray rates of40 to 60 ppm are recommended. A tankmix of B-Ninewat 2.500 ppm and Bonzi00 at 40 to 60ppm worked well. The tank mix using Bonzi® at 40 or60 ppm did not provide a synergestic effect becausethe degree ofcontrol was similar as when only Bonzi®was used. Greater synergestic effects occurred whenB-Nine® at 2,500 ppm was used with Bonzi® rates >80ppm. but that degree of control might be consideredexcessive by many growers. Based on these similarresults with Bonzi® alone at 40 or 60 ppm or incombination with B-Nine''. growers may find it easierto use Bonzi® alone (Figure 2).

These recommended rates are based on North Carolina

growing conditions. Growers in other locations willneed to modify the rates: with growers in morenorthern locations using slightly lower rates, whilemore southern growers should use slightly higherrates. All the foliar sprays were applied with a sprayvolume of 1 gallon over 200 square feet.

Figure 2. Plant growth regulator experiments withvegetative petunias (starting top row, left to right). C: Bonzi (0,40, 60, 80, 100,and 120ppm); Panel D:Panel A: A-Rest (0. 60, 80, 100. 120. and 140 ppm); (0, Bonzi at 60 ppm, Tank mix of Bonzi at 60 + B-Panel B: Sumagic(0.5, 10.20.30, and40ppm); Panel Nine at2,500 ppm). ^

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N.C. Flower Growers' Bulletin - February and April, 2002

SpacingWith these rapidly growing crops, there never isenough space. The petunias in particular, can easyintertwine, making shipping and marketing difficult.Watch the crop and apply growth retardants or cutback as needed to prevent tangled plants. Space plantsas far apart as possible.

PinchingPinching is not required; however, pinching can beused on strongly trailing petunia cultivars to encourageaxillary branching and bushier plants. Plants can bepruned and shaped at any time to reduce stretch andimproveaesthetics;however, floweringor refloweringwill be delayed by 2 or more weeks. Most of thepropagators suggest pinching the plants when they aretransplanted, and then repeatedly pinching at 3 to 4week intervals as needed.

Florel®at 500 ppm iseffective in increasing branchingon some cultivars, but may delayed flowering. Applywhen the roots reach the edge of the pot.

Schedule/TimingConsidering the rapid growth of petunias andcalibrachoas, crop time can be short. Four to 6-inchpots of petunias will finish in 5 to 7 weeks without apinch; add 2 or more weeks when pinching. Use onerooted cutting per 4 to 6-inch pot; shorter crop timecan be obtained with 2 cuttings per 6-inch pot.

Volume 47, Numbers 1 & 2

Plant 3 to 4 cuttings per hanging basket, which willfinish in 6 to 11 weeks. Late winter production willtake 1to 2 weeks longer than late spring due to highertemperatures and higher light levels. Calibrachoawill take 1 to 2 weeks longer than petunias.

Insects

Petunias and calibrachoa are more insect resistant

than many bedding plants, but whiteflies, thrips,aphids,caterpillars,and fungus gnatscan bea problem.

Diseases

Botrytis is a common problem on open flowers andcan quickly eliminate summer floral displays after arain or periods of high humidity. Be sure to provideadequate air movement and keep humidity below70% to reduce Botrytis. Powdery mildew and crownrot can also be problematic.

Physiological DisordersChlorosis can occur with iron deficiency (low pH),nitrogen deficiency, root rot, or low temperatures.

Postharvest

Petunia flowers are very sensitive to ethylene andexposure results in rapid wilting. Ethylbloc® islabeled for use on potted plants, but its efficacy onvegetatively-propagated petunias and calibrachoa isnot known.

Calendar of Events

Event Date Time Location and Contacts

Southeast Greenhouse

Conference and Trade

Show

June 19-22, 2002 All day Greenville, SC

(Contact SGCTC office at 800.453.3070)

Ohio Florists' Short

Course

July 13 to July 17,2002

All day Columbus, Ohio(Contact OFA office at 614.487.1117)

Bedding Plant Field Day July 26, 2002 All day Raleigh, NC(Contact Bonnie at 919.334.0093)

2002 International Plugand Cutting Conference

September 29 toOctober 2, 2002

All day Disney Coronado Springs ResortLake Buena Vista, FL

(Contact GrowerTalks at 888.888.0013)

Poinsettia Open House December 5, 2002,

December 8, 2002

9 am to 4 pm,1 pm to 4 pm

Raleigh, NC(Contact John Dole at 919.515.3537)

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