christopher j. currey volume 9 number 28 april2020 new ... · christopher j. currey...
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New Guinea Impatiens-
Do’s and Don’ts
New Guinea impatiens (Fig. 1) are one of the most popularbedding plants. Their attractive foliage and large, colorful,and plentiful flowers have made them an important annualcrop for grower. While they are not the hardest crop toproduce, they are not without their challenges. This articlehighlights the top “Do’s and Don’ts” for producing high-qualityNew Guinea impatiens.
TemperatureNew Guinea impatiens are a warm-growing crop and are
sensitive to cold temperatures. In contrast to early seasoncrops such as pansies, dianthus, and snapdragons, New Guineaimpatiens can struggle to grow in the greenhouse whentemperatures are too cool. Their optimal temperature, therate at which growth is fastest, is around 75 to 80 °F, whereastemperatures below 60 °F can slow down growth. Daytemperatures between 68 and 75° should be targeted. Whenrooted cuttings are first transplanted, it is best to maintainnight temperatures at or above 63 °F to get them established.Night temperature can be lowered slightly but should still bemaintained at or above 60 °F once root systems haveestablished and shoot growth resumes.
LightNew Guinea impatiens can flower under a range of day
lengths and are day-neutral plants. Although day lengthdoesn’t affect growth and flowering, the quantity of light- ordaily light integral (DLI)- does. A DLI of 4 mol·m–2·d–1 is
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Volume 9 Number 28 April2020
Christopher J. Currey
Figure 1. New Guinea impatiens are one of the most popular annual bedding plants, but they are not without their challenges.
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Figure 3. New Guinea impatiens are sensitive to the salt stress cause by excessive fertilization. The aborted shoot tips are signs of excessive substrate electrical conductivity. Compared to other vegetative propagated annuals, New Guinea impatiens require less fertilizer.
Figure 2. New Guinea impatiens will grow proportionally to the
water they are provided. Notice the tray or rooted cuttings on
the right hand side that has been held longer than the tray on
the left. In order to prevent wilting, cuttings were kept well-
watered- and look at the excessive growth it caused.
New Guinea Impatiens-Do’s and Don’ts
required for a minimally acceptable crop,while good- and high-quality crops aregrown under 6 to 8 mol·m–2·d–1 and 10 to15 mol·m–2·d–1, respectively. While DLIshigher 15 mol·m–2·d–1 should be avoidedfor many New Guinea impatiens cultivars,some of the newer varieties of NewGuinea impatiens developed for full suncan be grown under higher DLIs.Developed specifically for full-sunconditions in gardens, these these plantsare more adapted to the stronger lightintensity compared to traditional green-and bronze-leaf cultivars.
WaterIt is best to grow them on the slightly
drier side right after transplantingcuttings to let their root systemsestablish, and overwatering at this stagecan slow roots down from developing.Once established, the substrate can bekept moister. New Guinea impatiensgrowth responds positively to irrigation,and they are provided with as much wateras they can take up, growth is pushed tothe point of being excessive (Fig. 2).Therefore, restricting excessive irrigationis one effective method of non-chemicalgrowth control for this crop. However, becareful in moderating New Guineaimpatiens substrate moisture. If they arerepeatedly dried down too hard, plantswill suffer and they can even collapsefrom the repeated stress.
NutritionAvoiding over-fertilizing plants during
production is key for producing NewGuinea impatiens (Fig. 3). New Guineaimpatiens are light-feeding plants and arebest grown with a substrate electrical
Figure 4. While New Guinea impatiens generally do not require plant growth regulators (PGRs), the vigorous-growing cultivar on the left would have benefitted from some growth control, whether from better moisture management of chemical plantgrowth retardants.
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conductivity (EC) between 1.0 and 2.5mS/cm using the PourThru test. Providingtoo much fertilizer and allowing substrateEC to get too high can result in salt-stressed and -damaged plants. Oncecuttings are transplanted, fertilizerapplications are not required for the firstfew weeks as plants are establishing; thisis especially true if the substrate containsa starter charge. After plants are establishand start more active growth, fertilizercan start to be applied. Using 100 to 200ppm N at each irrigation, depending onirrigation leaching fraction, is sufficient.Incorporating clear water irrigations andleaching with clear water is useful toprevent high salts. In addition to managingEC, maintain substrate pH between 5.8and 6.2. New Guinea impatiens can besusceptible to micronutrient toxicity as pHdrops below 5.8.
Growth regulationIt is possible to produce New Guinea
impatiens with little to no plant growthregulator (PGR) application frompropagation through finishing. Cuttingsroot with without any rooting hormoneapplication. Modern New Guineaimpatiens cultivars are free-branching anddon’t require any pinching or othertreatments to enhance branching.Additionally, New Guinea impatiensgenerally do not require PGRs to supressgrowth, as this can be usually beaccomplished through cultural factorssuch as managing irrigation (Fig. 4). Ifgrowth retardants are needed,paclobutrazol sprays (1 to 15 ppm) arerecommended. For large containers withlong crop times, ethephon sprays (up to300 ppm) may be applied to abort flowersand buds and to
keep plants vegetative as they are bulkedup.
Pests and diseaseTomato spotted wilt virus (TSWV) and
impatiens necrotic spot virus (INSV) aretwo particularly devastating viruses forNew Guinea impatiens crops. Rigorouslyinspecting incoming cuttings and rootedliners for the necrotic lesions andconcentric rings. Additionally, stay on topof thrips control, as they are vectors forTSWV and INSV and can transmit theviruses to otherwise healthy plants. Alsokeep an eye on root rots that may developin New Guinea impatiens crops resultingfrom their water requirements.
Take-homeBy providing adequate heat and light,
adequate moisture, limiting excessfertilizer and drops in pH, and stayingahead of thrips and root rots, New Guineaimpatiens can finish strong (Fig. 5) forspring sales.
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Figure 5. These vibrant patio pots of New Guinea impatiens arejust finishing and ready to add some color to summer.
New Guinea Impatiens-Do’s and Don’ts
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CONTRIBUTORS
Dr. NoraCatlin
FloricultureSpecialistCornell Cooperative Extension
SuffolkCounty
Dr. ChrisCurreyAssistant Professor ofFloriculture
Iowa State University [email protected]
Dr. Ryan DicksonGreenhouse Horticulture and
Controlled-Environment AgricultureUniversity of Arkansas
Nick FlaxCommercial HorticultureEducator
Penn State [email protected]
Thomas FordCommercial HorticultureEducator
Penn State [email protected]
Dan Gilrein
Entomology SpecialistCornell Cooperative Extension
SuffolkCounty
Dr. Joyce LatimerFloriculture Extension & Research
Virginia Tech [email protected]
HeidiLindbergFloriculture Extension Educator
Michigan State University
Dr. RobertoLopezFloriculture Extension & Research
Michigan State [email protected]
Dr. NeilMattsonGreenhouse Research & Extension
Cornell [email protected]
Dr. W. GarrettOwenGreenhouse Extension & Research
University of [email protected]
Dr. Rosa E. Raudales
Greenhouse Extension Specialist
University of Connecticut
Dr. Beth ScheckelhoffExtension Educator – GreenhouseSystems
The Ohio State [email protected]
Dr. ArianaTorres-BravoHorticulture/ Ag. Economics
PurdueUniversity
Dr. Brian WhipkerFloriculture Extension & Research
NC StateUniversity
Dr. Jean Williams-WoodwardOrnamental Extension Plant Pathologist
University of Georgia
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