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Leonard P. Perry and Todd Herrick

Fifteen perennials were subjected to four to six (depending on species) levels of controlled freezing in chest freezers to determine killing temperatures. Average potting medium temperatures in six 1-liter pots of each species per freezing treatment were allowed to drop to target temperatures before plants were removed from freezers. Plants were held at 5 ± 2C for 3 months before freezing and for 24 hours after freezing before placing at 1 ± 2C. Two weeks after freezing, plant regrowth was rated on a scale of 1 to 5, 1 being dead, 3 being salable, 5 being normal (as controls of no freezing). Temperatures at which plants dropped below a 3 rating—not reliably hardy at that temperature—were –2C for Aster lateriflorus horizontalis and Tricyrtis formosana `Amethystina'; –6C for Caryopteris ×clandonensis `Longwood Blue', Phlox paniculata `David', Tiarella cordifolia collina `Oakleaf', Tricyrtis hirta `Miyazaki', and Veronica `Sunny Border Blue'; -9C for Astilbe `White Gloria', Hemerocallis `Joan Senior', Leucanthemum ×superburn `Alaska', and Tiarella c.c. `Dunvegan' and <13C for Monarda `Marshall's Delight', Phlox paniculata `White Admiral', Tiarella c. c. `Laird of Skye', and Achillea `Coronation Gold'.

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Marie-anne Boivin, Blanche Dansereau and André Gosselin

Green roof systems are now common in many European countries. Aside from aesthetic considerations, these systems present many environmental advantages in urban planning ecology. A flat roof surface (250 m2) was rebuilt on the top of a 30-year-old building. Our objective was to determine the effects of roof microclimate on the growth and development of six herbaceous perennials: Ajuga reptans, Arenaria verna `Aurea', Armeria maritima, Draba aizoides, Gypsophila repens, and Sedum Kamtschaticum. Rooted plants were transplanted into an artificial substrate at three depths (5, 10, and 15 cm) in a 36-m2 area. A special protective covering (Soprafiltre) was installed over the growing area. The following result are presented: temperature variations (winter–spring–summer) at crown and root-zone level, plant hardiness, growth index (height × width), and flowering.

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Nickolee Z, Roger Kjelgren, Teresa Cerny-Koenig, Rich Koenig and Kelly Kopp

We investigated drought responses of Echinacea purpurea, Gaillardia aristata, Lavandula angustifolia, Leucanthemum ×uperbum `Alaska', Penstemonbarbatus`Rondo', and Penstemo×mexicali `Red Rocks' established in a 10-gal pot-in-pot system in northern Utah. Plants were irrigated at frequencies of 1, 2, or 4 weeks between June and Sept. 2004. Osmotic potential, gas exchange, visual quality, leaf area, and dry biomass were assessed. In a confined root zone, P. barbatusshowed the greatest tolerance to drought, avoiding desiccation by increasing root: shoot ratio and decreasing transpiration as water became more limiting. Plants maintained high visual quality throughout the study and experienced little wilt, burn, or dieback. However, P. barbatus above-ground biomass was reduced by 15% for the 2-week treatment and by 40% for the 4-week treatment. Alternatively, G. aristata and L. superbum displayed drought avoidance mechanisms, dying back when water was limiting and resprouting after they were watered. Above-ground biomass declined by 50% and 84% for G. aristata and 47% and 99% for L. superbum, respectively, for the 2- and 4-week treatments. Root mass was affected similarly for both species. However, transpiration remained high for all treatment levels. Leaf burn and reduction in above- and below-ground biomass were also evident for E. purpurea at the 2- and 4-week treatments, but results were not as pronounced as for G. aristata and L. superbum. Overall, P. barbatusexhibited the greatest drought tolerance while maintaining an acceptable appearance. G. aristata, contrary to expectations, did not exhibit drought tolerance with a confined rooting volume, suggesting that it avoids drought in landscapes by means of deep rooting.

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Cheryl Hamaker, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Twenty species of perennials were trialed to determine the effectiveness of five growth retardants on final plant height and flowering. Growth retardant treatments consisted of five sprays: 100 ppm ancymidol, 1500 ppm chlormequat, 5000 ppm daminozide, 30 ppm paclobutrazol, or 15 ppm uniconazole. Also included for comparison were two drenches of 15 ppm paclobutrazol or 7.5 ppm uniconazole. Spray treatments consisted of one application every 10 days until anthesis. Drench treatments consisted of one application only. Data for days to visible bud and anthesis, bud number, and final height were collected. Plant response varied significantly between growth retardant treatments. Sprays of ancymidol, chlormequat, daminozide, paclobutrazol, and uniconazole effectively controlled the height of 4, 3, 13, 4, and 12 species, respectively. Daminozide and uniconazole were the most effective sprays at controlling height on a broad range of species. However, daminozide delayed anthesis compared to control treatments of at least 5 species. Drench treatments of paclobutrazol and uniconazole were effective on 14 and 15 species, respectively. The number of responsive species increased significantly when paclobutrazol was used as a drench rather than a spray. All species tested were responsive to at least one growth retardant treatment.

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Kelly J. Prevete, R. Thomas Fernandez and William B. Miller

Boltonia asteroides L. `Snowbank' (Snowbank boltonia), Eupatorium rugosum L. (eastern white snakeroot), and Rudbeckia triloba L. (three-lobed coneflower) were subjected to drought for 2, 4, and 6 days during the fall and spring. Leaf gas exchange, leaf water potential, growth, and carbohydrate partitioning were measured during drought and throughout the following growing season. Leaf gas exchange of B. asteroides was not affected by drought treatment in the fall, not until day 6 of spring drought, and there were no long-term effects on growth. Transpiration and stomatal conductance of R. triloba decreased when substrate moisture decreased to 21% after drought treatment during both seasons. Assimilation of drought-treated R. triloba decreased when substrate moisture content decreased to 12% during spring but was not affected by drought in the fall. There was a decrease in the root-to-shoot ratio of R. triloba that had been treated for 4 days, which was attributed to an increase in the shoot dry weight (DW) of treated plants. Reductions in spring growth of E. rugosum were observed only after fall drought of 6 days, and there were no differences in final DWs of plants subjected to any of the drought durations. Spring drought had no effect on growth index or DW of any of the perennials. Boltonia asteroides and R. triloba had increases in low-molecular-weight sugars on day 4 of drought, but E. rugosum did not have an increase in sugars of low molecular weight until day 6 of drought. Differences in drought response of B. asteroides, E. rugosum, and R. triloba were attributed to differences in water use rates.

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Catherine M. Whitman and Erik S. Runkle

marketed most successfully. Ornamental herbaceous perennials have posed some unique challenges to growers attempting to produce uniform crops in flower consistently. This has prompted research into the flowering requirements of a wide range of herbaceous

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Kimberly A. Klock and Nancy Howard Agnew

Problems with iron toxicity are documented for the bedding plant species of geranium and marigold. It was suspected that observed nutrition problems of Chrysanthemum Xsuperbum `Snow Lady' were due to iron toxicity. The objectives of this study were to determine which if any perennial species were sensitive to iron toxicity (iron efficient) and to document any symptoms. Using a sand culture method, C. Xsuperbum `Snow Lady' and `Alaska', and Pelargonium Xhortorum `Red Elite' (as a check) and 3 other perennial species were watered twice daily with a modified Hoaglands I solution with 0.00, 0.02, 0.04, 0.08, 0.16, or 0.32 mM FeEDTA. Only Pelargonium had toxic foliar iron levels (462.2 ppm Fe averaged over all treatments) and showed classic iron toxicity symptoms. C. Xsuperbum `Alaska' showed possible iron toxicity symptoms at 0.08 and 0.16 mM FeEDTA with foliar iron levels of 301.0 ppm Fe and 282.7 ppm Fe, respectively. Below average foliar levels of Mn were observed in all species except Pelargonium. Also noted were: toxic levels of boron in Achillea and deficient levels of copper in Aguilegia.

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R. Thomas Fernandez, Ted Whitwell, Melissa B. Riley and Cassandra R. Bernard

Canna ×generalis L.H. Bail. (canna), Pontaderia cordata L. (pickerel weed), and Iris L. × `Charjoys Jan' (`Charjoys Jan' iris) were exposed to a 5 mg·L-1 suspension of isoxaben or oryzalin or a water control for 9 days. Growth and photosynthetic responses were monitored throughout treatment and for an additional 22 d after termination of treatment. By the end of the experiment plant height of pickerel weed was reduced by oryzalin. Isoxaben resulted in lower height and reduced leaf emergence for all three taxa by the end of the experiment. Leaf CO2 assimilation (A) and transpiration (E) were lower for oryzalin-treated canna only 17 and 18 days after treatment, several days after treatment had been terminated. Leaf A and E were lower for oryzalin-treated pickerel weed and `Charjoys Jan' iris for most days after day 17. Isoxaben reduced A and E of all three plants for all days measured except day 6 for `Charjoys Jan' iris. Lower photosystem II efficiency (Fv/Fm) was found for isoxaben-treated canna from day 5 onward and days 7, 20, and 23 for pickerel weed and `Charjoys Jan' iris. Rapid reduction in A and Fv/Fm for all plants treated with isoxaben indicates a direct effect of isoxaben on photosynthesis. Reductions in growth and photosynthetic parameters due to oryzalin were minimal for all plants indicating these plants would be useful in phytoremediation systems where oryzalin is present. However, growth and photosynthetic parameters were reduced substantially for all plants exposed to isoxaben indicating the taxa studied would not perform well in phytoremediation systems with this level of isoxaben exposure. Chemical names used: isoxaben (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyly]-2,6-dimethoxybenzamide); oryzalin (4-(dipropylamino)-3,5-dinitrobenzenesulforamide).

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Anne M. Hanchek and Arthur C. Cameron

The effect of harvest dates between September and December on regrowth after storage of field-grown Coreopsis grandiflora Hogg × Sweet `Sunburst' and `Sunray', Geum quellyon Sweet `Mrs. Bradshaw', Gypsophila paniculata L. `Snowflake', Iberis sempervirens L. `Snowflake', and Dicentra spectabilis (L.) Lem. crowns was determined. After 0 to 7 months of storage at 0C, stored crowns were repotted and grown in a greenhouse. Plants from later harvests were of higher quality than those from earlier harvests, showing higher rates of survival after longer storage periods, less mold development in storage, and stronger regrowth after storage. Late field harvest is recommended for optimum storage quality.

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Cheryl Hamaker, William H. Carlson, Royal D. Heins and Arthur C. Cameron

DIF is the difference between day (DT) and night (NT) temperatures. Temperature drop is a 2-hour temperature reduction at sunrise. DIF and temperature drop, which can be affected by light quality, are effective methods to control final plant height of many greenhouse crops. The effect of DIF and temperature drop on final height was determined for eight species of perennials. Durations for DIF temperatures were 12 hours for both DT and NT. Temperature alterations occurred at sunrise. Temperature treatments (DT/NT) consisted of zero DIF (20/20°C), negative DIF (16/24°C), or positive DIF (24/16°C), and a 2-hour drop (12.7/20.7°C). Long days (LD) were provided from 2200-0200 hr by either cool-white fluorescent (CWF) or incandescent (INC) lights. Data for days to visible bud and anthesis, bud number, and final height were collected. Positive DIF conditions enhanced elongation while negative DIF reduced it in all species. As DIF decreased from positive to negative, plant height was reduced 10%, 30%, 30%, and 20% in Coreopsis `Moonbeam' and `Sunray', Delphinium `Belladonna', and Scabiosa `Butterfly Blue', respectively. Negative-DIF responses were enhanced under CWF lights for some species. In negative-DIF conditions, Coreopsis `Moonbeam' and `Sunray' and Delphinium `Belladonna' were 10%, 10%, and 15% shorter, respectively, under CWF lights than INC lights.