A survey was conducted to identify and characterize the effectiveness of overwintering methods used to protect container-grown herbaceous perennials in USDA hardiness zones 3 through 8. Survey questionnaires were sent by first-class mail on 20 Aug. 1996 to 634 firms involved in growing and/or selling container-grown herbaceous perennials identified from the Perennial Plant Association Membership Directory. Completed questionnaires were received from 293 individuals (46.2% response rate) in 38 states, the District of Columbia, and six Canadian provinces. Survey participants reported using several overwintering methods: structureless systems (71.0%), polyhouses (52.9%), polyhouses with inflated double polyethylene covers (30.7%), and low-profile polyhuts (12.3%). Over three-fourths of the respondents (78.8%) said their winter protection methods resulted in minimal to no plant loss (0-10%). Only 53 respondents (18.1%) reported losses >10%. The most frequently cited reason for plant loss across all hardiness zones was excessive moisture inside the overwintering environment (50.2%). Equal percentages (33.4%) indicated low temperatures and damage from animals as the next most likely factors responsible for plant loss. Respondents identified, in descending order, Iris, Delphinium, Lavandula, Papaver, and Lupinus as the five genera most difficult to overwinter.
Holly L. Scoggins
Little taxa-specific information is available regarding the nutrition needs of container-grown herbaceous perennials. The goal was to determine optimum fertilizer concentrations and corresponding substrate testing values for greenhouse production of 10 taxa. Astilbe chinensis (Maxim.) Franch. & Savat.`Purpurkerze', Campanula carpatica Jacq. `Deep Blue Clips', Coreopsis verticillata L.`Golden Gain', Gaura lindheimeri Engelm. & Gray, `Siskiyou Pink', Heucherasanguinea Engelm. `Mt St. Helens', Lamium maculatum L. `White Nancy', Penstemon ×hybridus Hort. `Sour Grapes', Perovskia atriplicifolia Benth. `Longin', Salvia nemerosa L. `Blue Hill', and Veronica × Hort. `Goodness Grows' were grown for 10 weeks with 15N–7P–14K at four rates (50, 150, 250, and 350 mg·L–1 N) of constant liquid feed. Substrate pH and soluble salts levels were measured weekly using the pour-through extraction method. In analysis of all taxa, most effects [quality, shoot dry weight, pH and electrical conductivity (EC)] varied by rate × taxa. Though higher levels of fertilizer produced the largest plants in some cases, satisfactory quality was also attained with a lower rate. Quality and pH were negatively correlated for a few genera but most showed no relationship. Results of this study indicate not all taxa tolerate increased fertilizer levels and that the herbaceous perennials studied could be grouped by nutritional needs. Furthermore, target ranges for EC can be developed based on dry mass and quality ratings.
Jeffery K. Iles and Nancy H. Agnew
The capacity of plant materials to resume normal growth after exposure to low temperature is the ultimate criterion of cold hardiness. We therefore determined the low-temperature tolerance of five commercially important herbaceous perennial species. Container-grown blanket flower (Gaillardia ×grandiflora Van Houtte. `Goblin'), false dragonhead [Physoste- gia virginiana (L.) Benth. `Summer Snow'], perennial salvia (Salvia ×superba Stapf. `Stratford Blue'), painted daisy (Tanacetum coccineum Willd. `Robinson's Mix'), and creeping veronica (Veronica repens Loisel.) were subjected to 0, -2, 4, -6, -8, -10, -12, -14, -16, and -18C in a programmable freezer. The percentage of survival of most species was adequate when exposed to -10C. Producers of container-grown perennials are advised to provide winter protection measures that prohibit root medium temperatures from falling below -10C.
David Hillock and James E. Klett
Four herbaceous perennials Aquilegia caerulea `McKana's Giant', Gaillardia aristata, Gypsophila paniculata `Fairy's Pink', and Callirhoe involucrata were subjected to increasing levels of drought stress and evaluated for ornamental quality and performance in the landscape. Drought stress was imposed by irrigation treatments of 100%, 75%, 50%, 25%, and 0% of reference evapotranspiration (ET0) in 1994. Irrigation treatments resulted in Aquilegia exhibiting a decline in plant growth and appearance below the 50% ET0 treatment. Callirhoe grown at the 100% ET0 irrigation treatment were larger than the plants in any other treatment. Gaillardia receiving some irrigation (25% to 100% ET0) were generally larger than those that received no supplemental irrigation (0% ET0). A decline in plant appearance and growth was observed with Gypsophila with lowering irrigation treatments.
Yan Chen, Regina Bracy and Roger Rosendale
While herbaceous perennials continuously gain popularity in southern landscape plantings, the nutrient requirements of many species in this group are still unknown. The business goal of lawn and garden care companies emphasizes aesthetic value of the urban landscape. Improper nutrient management, such as the overapplication of fertilizers, is inefficient and may result in increased pest problems and risks of contaminating ground and surface waters by nutrient runoff. Seven herbaceous perennials (lantana, rudbeckia, purple cone flower, daylily, mexican heather, cigar plant, and guara) were planted in simulated landscape beds. Fertilizers applied included one or two OsmocotePlus 16-8-12 tablets (7.5 g), OsmocotePlus 15-9-12 (5 months) at 0, 33, 66, and 131 g/m2 at planting, or applying OsmocotePlus 15-9-12 (5 months) 33 g/m2 or one OsmocotePlus tablet at the time of planting plus another 33 g/m2 topdressing after flowering. Plant growth of rudbeckis, purple cone flower, and lantana were highest at 131 g/m2 applied at planting, but resulted in similar overall plant quality as with 33 or 66 g/m2 treatments. Daylily growth was similar across fertilization treatments, and overall quality decreased at high fertilization rates with more severe daylily rust observed on these plants. Applying one OsmocotePlus 7.5-g tablet resulted in similar plant quality with applying OsmocotePlus 33 and 66 g/m2, but significantly reduced the amount of fertilizer used. Additional topdressing after flowering did not further increase plant quality in fall, but may affect the overwintering survival of perennial plants.
Holly L. Scoggins* and Joyce G. Latimer
Increasing fertilizer levels may reduce production time but can lead to excessive growth of herbaceous perennials, requiring the application of plant growth regulators (PGRs). This study investigated the effects of ascending fertilizer rates in conjunction with two rates of uniconazole and a control. Rooted liners of Artemisia arborescens L. `Powis Castle', Artemisia vulgaris L. `Oriental Limelight, Astilbe chinensis (Maxim.) Franch. `Pumila', Filipendula rubra (Hill) Robinson `Venusta' and Perovskia atriplicifolia Benth. were potted with controlled-release fertilizer (15N-3.9P-10K) incorporated at 2.4, 4.72, and 7.11 kg·m-3. A single foliar spray application of uniconazole was applied two weeks after transplanting at a volume of 210 mL·m-3 and two rates from 15 to 60 mg·L-1 plus a control (species-dependent). Plant height and width were measured at 2,4,6, and 8 weeks after treatment (WAT). No interactions between fertilizer rate and uniconazole were observed. Main effects varied by species. The application of uniconazole controlled height and width of Artemisia `Oriental Limelight' and Astilbe for the duration of the experiment. Height, width, and dry weight of Artemisia `Oriental Limelight' increased with ascending fertilizer rates while Astilbe was not affected. Growth of Filipendula and Artemisia `Powis Castle' was unresponsive to uniconazole, though dry weight was reduced for both at the lowest fertilizer rate. Uniconazole provided height control of Perovskia, but the effect did not persist beyond 6 WAT. Ascending fertilizer rates increased Perovskia dry weight but not height.
Jeffery K. Iles and Nancy H. Agnew
Nine herbaceous perennial species were evaluated for use as flowering pot plants for late winter and early spring sales. Plugs of Achillea `King Edward', Arabis sturii, Armeria `Alba', Bergenia `New Hybrid', Chrysogonum virginianum, Dianthus `War Bonnet', Phlox `Chattahoochee', Platycodon `Sentimental Blue', and Veronica `Sunny Border Blue' were established in 14-cm (0.8-liter) round plastic containers, grown for one season, and covered with a thermoblanket for winter. Five plants of each species were transferred to a 21 ± 3C glasshouse for forcing under natural daylength at six 10-day intervals beginning 1 Dec. 1993. By this date plants had experienced approximately four weeks of temperatures below 5C. Ambis, Chrysogonum, and Phlox, species that naturally flower in spring, were the most floriferous. Days to first flower for Arabis decreased from 30 to 26 while flower number increased 44% by the 20 Dec. forcing date. For Phlox, days to first flower decreased from 36 to 31 by 20 Dec., but flower numbers were similar regardless of forcing date. Chrysogonum averaged eight flowers throughout the study, but days to first flower increased from 25 (1 Dec.) to 31 in all following forcing dates.
Terri Starman and Leonardo Lombardini
A study was conducted to characterize the morphological and physiological responses of four herbaceous perennial species subjected to two subsequent drought cycles. Lantana camara L. `New Gold' (lantana), Lobelia cardinalis L. (cardinal flower), Salvia farinacea Benth. `Henry Duelberg' (mealy sage), and Scaevola aemula R. Br. `New Wonder' (fan flower) were subjected to two consecutive 10-day drought cycles. Growth response, leaf gas exchange, and chlorophyll fluorescence were measured during the experiment. The morphology of L. cardinalis and L. camara was not affected by drought, while S. farinacea had reductions in plant height and leaf area and S. aemula had reductions in dry weight. Overall, plant growth and development continued even when substrate water content was reduced to 0.13 mm3·mm-3, which indicated a level of substrate water below container capacity was sufficient for greenhouse production of these species. The drought treatments had little effect on the photochemical efficiency (Fv/Fm) of Photosystem II. An increase in minimal fluorescence (Fo) was observed in S. aemula on the last day of the second cycle. Drought treatment caused increased leaf-level water use efficiency (WUE) at the end of the first cycle in L. cardinalis and S. aemula, but not in L. camara and S. farinacea. Plants of L. camara, S. farinacea, and S. aemula that had received drought during both cycles became more water use efficient by the end of the second cycle, but L. cardinalis did not.
Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson
Thirty herbaceous perennial species were treated at 5°C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours plus a 4-hour night interruption. Continuous photo-periodic treatments consisted of 9-hour natural days extended with light from incandescent lamps. Species were categorized into nine response types based on the effects of cold and photoperiod on flowering. Plants had three flowering responses to cold treatment: obligate, facultative, or none. The perennials were obligate long-day, facultative long-day, or day-neutral plants. For example, Campanula carpatica `Blue Clips' had no response to cold and was an obligate long-day plant requiring photoperiods of 16 hours or longer or night interruption for flowering. Rudbeckia fulgida `Goldsturm' had a facultative response to cold and required photoperiods of 14 hours or longer or night interruption for flowering. Veronica longifolia `Sunny Border Blue' had an obligate cold requirement and was day-neutral. Some species responded differently to photoperiod before and after cold. Leucanthemum ×superbum `Snow Cap' flowered as an obligate long-day plant without cold and as a facultative long-day plant after cold. Response categories are discussed.
Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson
Twenty-four herbaceous perennial species were treated at 5C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 14, 16, and 24 h of continuous light and 9 h plus a 4-h night interruption. Continuous photoperiodic treatments consisted of 9-h natural days extended with light from incandescent lamps. Response to cold and photoperiod varied by species; Scabiosa caucasica `Butterfly Blue' flowered without a cold treatment under all photoperiods after 8 to 10 weeks of forcing, but plant height increased from 14 to 62 cm as daylength increased. Rudbeckia fulgida `Goldsturm' flowered without cold after 13 to 15 weeks of forcing, but only under 16 hours of continuous light and night interruption treatments. Heuchera sanguinea `Bressingham Hybrids' did not flower without cold under any photoperiod but did flower under all photoperiods with cold. The only Lavendula angustifolia `Munstead Dwarf' plants that flowered without cold were those under 24-h continuous light; ≈60% flowered. After cold, some lavender plants flowered under all photoperiods, and the flowering percentage increased with increasing daylength.