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Roberta J. Tolan and James E. Klett

Patmore green ash (Fraxinus pennsylvanica `Patmore'), Bur oak (Quercus macrocarpa), and Austrian pine (Pinus nigra), were used to measure growth differences of trees produced using three different production methods: balled and burlapped, plastic container, and fabric container (grow bag). Two irrigation frequencies were also established. A pressure chamber was used to measure the xylem water potential and to determine tree water requirements and irrigation scheduling. The balled and burlapped trees showed the least new growth of the three production methods across all three tree types. The production method showing the most new growth varied by genera. Plastic container ash trees grew considerably more than the fabric container ash; fabric container oak grew significantly more than plastic container oak; and there was no measurable difference between the new growth of the plastic container and fabric container pines. The fabric container transplants required more frequent irrigation than did the balled and burlapped trees. Under high temperature and drought conditions, fabric container trees showed stress earlier than did the balled and burlapped or plastic container trees.

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Jennifer M. Bousselot, James E. Klett, and Ronda D. Koski

This research examined plant area covered (plant cover) for six plant species on an existing modular extensive green roof in a semiarid climate. Species evaluated were Antennaria parvifolia Nutt., Bouteloua gracilis (Kunth) Lag., Delosperma cooperi (Hook. f.) L. Bol., Eriogonum umbellatum Torr. aureum ‘Psdowns’, Opuntia fragilis Nutt., and Sedum lanceolatum Torr. Many methods for measuring plant cover are subjective and based on semiquantitative measurements. This study compared digital image analysis data (DIA) with manually collected converted two-dimensional data (C2D) for plants grown on an extensive green roof. For each plant in the study, digital images and manual two-dimensional measurements were taken on four dates (at 6-week intervals) in 2008 and on four dates (at 6-week intervals) in 2009. Additionally, comparisons between DIA data and final biomass, and C2D and final biomass, were performed. Plant cover increased for all six species during the 2008 growing season. However, E. umbellatum aureum ‘Psdowns’ had a low overwintering rate (12.5%) and was removed from analysis in 2009. In the spring of 2009, four of the five remaining species exhibited decreased plant cover as a result of winter dieback; the one exception was O. fragilis. In terms of plant cover, both quantification methods (C2D and DIA) revealed that B. gracilis and D. cooperi had more plant cover than A. parvifolia, O. fragilis, and S. lanceolatum by the end of the study. Thus, five of the six species evaluated in this study are appropriate for use in extensive green roof applications in semiarid regions. High levels of correlation were found between the DIA and C2D data sets (r = 0.77) averaged over the five species on all eight data collection dates. The groundcover species (A. parvifolia, D. cooperi, and S. lanceolatum) had a higher correlation on average (r = 0.83) than the upright (B. gracilis, r = 0.70) and decumbent (O. fragilis, r = 0.65) species. Additionally, DIA and final biomass correlations showed parallel trends with groundcovers averaging r = 0.83, upright r = 0.64, and decumbent r = 0.41. Therefore, using DIA to evaluate plant cover and biomass accumulation is especially appropriate for groundcover species.

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Dianne Oakley, Julie Laufmann, James Klett, and Harrison Hughes

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

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Harrison Hughes, Elizabeth Mogen, Steven Newman, James Klett, and Anthony Koski

An assessment plan for the Horticulture and Landscape Horticulture majors has been developed as part of a university-wide effort to assess resident instruction. The program mission has been described as the preparation of graduates with a passion for Horticulture/Landscape Horticulture who can contribute to Colorado's agricultural and green industry economy through high levels of: 1) technical competency and skills, including disciplinary competence, and a working knowledge in the appropriate field; 2) management and leadership skills; and 3) problem-solving skills. Assessment methods involved the development of evaluation forms for internships, practicum, independent study, group study, and the capstone courses. Student, faculty, clients, and industry personnel used standardized forms, which varied somewhat for the two majors and seven concentrations, to critically assess and score student and faculty efforts. Internships, practicum, and capstone courses were evaluated for program purpose. The management and leadership skills of the students were evaluated based on their performance during internships by cooperators and also by their activities, as demonstrated through their involvement in university, college, departmental, and community activities. Problem-solving skills were evaluated primarily through student performance in capstone courses, with specific criteria in the internship and in leadership activities of clubs. The expectation is that 70% to 75% of the students will score 3 or 3+ on all criteria established for a rating system of 1–5. Students have generally met this standard and plans are under way to continually upgrade courses and related activities to improve the teaching program

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David Staats, James Klett, Teri Howlett, and Matt Rogoyski

During the 2005 season, three preemergence herbicides were applied to four container-grown herbaceous perennials and evaluated for weed control, phytotoxicity, and effect on plant growth. The herbicides and application rates were: 1) Pendimethalin (Pendulum 2G) 2.24, 4.48, and 8.96 kg/ha; 2) Trifluralin and Isoxaben (Snapshot 2.5 TG) 2.8, 5.6, and 11.2 kg/ha; and 3) S-metolachlor (Pennant Magnum 7.6 EC) 2.8, 5.6, and 11.2 kg/ha. Herbicides were applied to Coral Bells (Heuchera sanguinea), Hopflower Oregano (Origanum libanoticum), CORONADO™ Hyssop (Agastache aurantiaca), and SPANISH PEAKS™ Foxglove (Digitalis thapsi). Treatments were applied twice with 30 days between applications. Plants were evaluated for phytotoxicity after 1, 2, and 4 weeks after applying herbicide treatments. No phytotoxicity symptoms were apparent on any of the plants treated with Pendulum, and plant size (dry mass) was not affected. Snapshot resulted in visual phytotoxicity with Digitalis and Heuchera at the higher rates and also resulted in smaller plants. Pennant Magnum caused phytotoxicity at all rates in all plants and resulted in significantly smaller plants than the control. Weed control was very good with all herbicides, but did not control every weed.

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Jennifer M. Bousselot, James E. Klett, and Ronda D. Koski

Success of extensive green roof vegetation depends primarily on associated plant species' ability to survive the low moisture content of the substrate. As a result of the well-drained nature of the substrate, plants adaptable to dry, porous soils are primarily used in extensive green roof applications. Although Sedum species have dominated the plant palette for extensive green roofs, there is growing interest in expanding the plant list for extensive green roof systems. To effectively select suitable plants, species need to be evaluated in terms of their response to gradual and prolonged dry down of the substrate. A study to determine the relative rates of dry down for 15 species was conducted in greenhouse trials. During dry downs that extended over 5 months, the substrate of succulent and herbaceous species dried down at different rates. The change in moisture content of the substrate was not consistent among succulent and herbaceous plant species during the initial 18 d of dry down. Despite differences in rate of dry down, the succulent species, as a group, maintained viable foliage for over five times longer than the herbaceous species. The revival rates of the succulent species were nearly double those of the herbaceous species. Therefore, not only are succulent species more likely to survive during periods of drought, but these species are more likely to resume growth soon after water is again made available.

Open access

Shana G. Brown and James E. Klett

Stock plant productivity is an important concern for growers of ‘Snow Angel’ coral bells (Heuchera sanguinea) because this variety produces a limited number of basal cuttings. The objective of the study was to determine the best growth substrate and container size combination to maximize productivity of stock plants. A secondary objective was to determine if the stock plant treatments influenced the rooting of vegetative cuttings. The study used three different container sizes (2.8, 11.4, and 14.6 L) and four commercial soilless substrates that were primarily composed of the following: bark, peat, and perlite (substrate 1); bark, peat, and vermiculite (substrate 2); bark, peat, and coarse perlite (substrate 3); and peat (substrate 4). Two stock plant experiments were conducted using the same 12 treatment combinations, and a subset of those stock plants was randomly selected for the rooting studies that immediately followed each stock plant experiment. Stock plants responded to substrate treatments differently depending on the batch of substrate in which they were grown. The most successful stock plants, which produced more cuttings per plant and per square foot, as well as larger cuttings, were those grown in substrate 3 (Expt. 1) and substrate 2 (Expt. 2). Regardless of the substrate, the highest number of cuttings per square foot was obtained from stock plants grown in 2.8-L containers, indicating that the smaller containers allow for the most efficient use of space when growing ‘Snow Angel’ stock plants for 6 to 8 months. The rooting of vegetative cuttings was successful (98% to 100% of cuttings rooted after 4 weeks under mist) for all treatment combinations, although higher numbers of visible roots were produced during the second study and may be due to larger fresh weights of cuttings.

Open access

Sean J. Markovic and James E. Klett

The objective of these experiments was to evaluate the reaction of ‘Snow Angel’ coral bells (Heuchera sanguinea) and Orange Carpet hummingbird trumpet (Epilobium canum ssp. garrettii ‘PWWG01S’) to repeated foliar applications of three plant growth regulators at two application rates. The plant growth regulators applied during a stock plant study and followed by a propagation study were 200 and 400 ppm ethephon, 250 and 500 ppm benzyladenine, and 50 and 100 ppm gibberellic acid 4 and 7 (GA4+7) + benzyladenine. The stock plant study was conducted to assess the efficacy of plant growth regulators, vegetative growth (height and width growth index), the number of vegetative cuttings, as well as the fresh weight (FW) and dry weight (DW) of the harvested vegetative cuttings. The propagation study was conducted to determine the effects of the plant growth regulator treatments on the rooting of the vegetative cuttings. The stock plant study showed that GA4+7 + benzyladenine (50 and 100 ppm) significantly increased production of ‘Snow Angel’ coral bells cuttings compared with all other treatments. However, no significant differences in FW or DW were observed with ‘Snow Angel’ coral bells between treatments. In the propagation study, no significant difference in rooting percentage was observed after 4 weeks. The Orange Carpet hummingbird trumpet stock plant study resulted in a greater number of vegetative cuttings with GA4+7 + benzyladenine (50 and 100 ppm) and benzyladenine (250 ppm) treatments. Fresh weight of vegetative cuttings harvested from plants treated with GA4+7 + benzyladenine (50 or 100 ppm) were the lowest. The only treatment that showed increased vegetative cutting production with no effect on FW was benzyladenine (250 ppm) on Orange Carpet hummingbird trumpet.

Full access

Larry A. Rupp, Richard M. Anderson, James Klett, Stephen L. Love, Jerry Goodspeed, and JayDee Gunnell

In response to a perceived need for the development and introduction of superior plant accessions for use in sustainable, low-water landscaping, land-grant universities in Colorado, Idaho, and Utah, have supported plant development programs. Each of these programs has unique characteristics and protocols for releasing plant materials and obtaining royalties to further support research and development. Colorado State University (CSU) is part of the Plant Select program, which evaluates and promotes native and non-native plants for use in low-water landscapes. Selected plants are released to commercial members who pay a membership fee and royalties for access to the selected plants. The University of Idaho focuses on selecting and evaluating native herbaceous perennials, which are then released through a contract and royalty program with a local nursery. Utah State University uses the Sego Supreme program to select, propagate, and evaluate native plants. Selected plants are released to interested growers who pay a royalty for production rights.

Open access

Sean J. Markovic, Shana G. Brown, and James E. Klett

Stock plant productivity is an important concern for growers of mojave sage (Salvia pachyphylla) because this species produces more woody growth as the plant ages. The objective of the study was to determine the best growth substrate and container size combination to maximize stock plant productivity. A secondary objective was to determine whether the stock plant treatments influenced the rooting of vegetative cuttings. Three different container sizes (3, 12, and 15.5 qt) and four soilless substrates composed primarily of bark, peat, and perlite (substrate 1); bark, peat, and vermiculite (substrate 2); bark, peat, and coarse perlite (substrate 3); and peat (substrate 4) were used. The stock plant experiment was conducted using 12 treatment combinations, and a subset of those stock plants was selected randomly for the rooting study that immediately followed the stock plant experiment. Stock plants responded to substrate treatments differently. The most successful stock plants, which produced more cuttings per plant and per square foot, as well as larger cuttings, were those grown in substrate 3. Regardless of substrate, the highest number of cuttings per square foot was obtained from stock plants grown in 3-qt containers, indicating that the smaller containers allow for the most efficient use of space when growing mojave sage stock plants for 4 to 6 months. The rooting of vegetative cuttings was successful (88% to 100% of cuttings rooted after 4 weeks under mist) for all treatment combinations.