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Dennis R. Pittenger

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Dennis R. Pittenger

The performance of six landscape groundcover species was evaluated in a field experiment with irrigation treatments of 50%, 40%, 30%, and 20% of real-time ET0. Analysis of seasonal plant performance ratings indicated that for Baccharis pilularis `Twin Peaks', Drosanthemum hispidum, and Hedera helix `Needle point' there were no season-long increases in plant appearance when irrigated more than 20% ET0. Vinca major, Gazania hybrid, and Potentilla tabernaemontanii exhibited no significant improvement in appearance when irrigated above 30% ET0. A marked decline in performance was apparent in Gazania and Potentilla at all treatments during the study period, however, suggesting that their long-term minimum irrigation needs exceed 50% ET0. In a follow-up study, five of the above species and Osteospermum fruticosum received 30% ET0 at irrigation schedules of three times/week, once/week, once/2 weeks, and once/4 weeks. Potentilla was not sustained in acceptable condition at any treatment, while there were no season-long differences in performance within the other species due to irrigation frequency.

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Donald R. Hodel and Dennis R. Pittenger

The objectives of this study were to investigate the responses of several groundcovers to periodic mowing and determine which ones benefit from mowing in terms of aesthetic quality, density, height and thatch development.

Eight species were transplanted on 30 cm centers in September. Five species had become fully grown in 10 months and were mowed to either a 5 cm or 10 cm height. Four species received a second mowing at 10 cm 8 or 11 months later. The remaining three species became fully grown in 18 or 21 months and were mowed at 10 cm at that time. Visual quality scores were recorded monthly, as were average overall plant and thatch heights. Lantana, Osteospermum and Verbena expressed little or no long-term loss in visual quality, while their height and thatch growth were controlled well when mowed in the spring-summer period. Height and thatch growth were controlled well in Drosanthemum and Aptenia, but visual quality was unacceptable. Spring mowing appears to produce reductions in height and thatch with no significant loss in quality of Myoporum and Baccharis but with significant loss in quality of Rosemarinus.

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Ursula K. Schuch and Dennis R. Pittenger

This study was designed to determine whether trees growing in tall, narrow containers versus regular containers of equal volume, or trees growing in containers coated with cupric hydroxide versus no coating would have a better quality root system, less circling roots, and more biomass production. Ficus (Ficur retusa L. `nitida') and pepper (Schinus terebinthifolius Raddi.) liners were grown for 6 months in the greenhouse in one-gal. containers. Cupric hydroxide coating prevented matting of roots on the side of the root ball in both species and root circling at the bottom of containers in ficus. Pepper trees growing in regular-shaped containers had a higher biomass production versus trees growing in tall containers. Subsequently, trees were transplanted to 3 or 5 gal. containers with shape or coating as described above. For pepper, cupric hydroxide coating versus no coating reduced circling and matting of roots, trees in regular versus tall containers had increased above ground biomass, and trees in 5-gal. versus 3-gal. containers grew more medium and small-sized roots and produced more total biomass.

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Dennis R. Pittenger, Donald R. Hodel and A. James Downer

Successful reestablishment of transplanted palms [members of the Arecaceae (Palmae)] depends on rapid regeneration of roots, avoiding injury and desiccation of the trees during transit and handling, and maintaining sufficient soil moisture around the root balls after transplanting. Since landscape contractors and nurserymen spend considerable resources and labor transplanting specimen palms, understanding the seasonality of palm root growth, how palm roots respond when trees are dug, and the effects of canopy manipulation during transplanting will enable them to adopt effective and rational transplanting practices. This manuscript provides a review of research findings that can be applied to maximize reestablishment of transplanted specimen palms.

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Donald R. Hodel, A. James Downer and Dennis R. Pittenger

The optimum time to transplant palms (Arecaceae) is at the beginning of the warm season in temperate climates or at the beginning of the rainy season in tropical climates if irrigation is unavailable. Careful and proper handling, including covering and protecting the leaves and root ball during transplanting to protect them from injury and drying out and immediate planting upon arrival at the new site, helps to ensure rapid and successful establishment. A root ball extending out from the trunk for 30 cm appears to be adequate for most solitary-stemmed species. Larger root balls may be necessary for multistemmed or unusually tall or large specimens. Tying up leaves facilitates handling during digging, transport, and planting, but it is best to untie them after planting. In most instances leaf removal during transplanting does not appear to be advantageous, and it is probably best to remove leaves only when they die and turn brown. Too deep or too shallow planting lowers transplant success and stresses palms, making them susceptible to diseases, disorders, and pests. Amending the backfill when transplanting palms is not beneficial in most cases. However, mulch applied around the base of the palm after transplanting can enhance growth. Keeping the soil, backfill, and surrounding site soil evenly moist helps to ensure successful establishment.

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Dennis R. Pittenger, David A. Shaw and William E. Richie

We conducted an evaluation of three commercial weather-sensing irrigation controllers to determine the climatic data they use, how easy they are to set up and operate, and how closely their irrigation regimes match landscape irrigation needs established by previous field research. The devices virtually controlled an existing reference irrigation system and used its system performance data as required in their initial setup. Reference standard treatments for cool-season turfgrass, trees/shrubs and annual flowers were calculated using onsite, real-time reference evapotranspiration (ETo) data and plant factors developed primarily from previous research. The reference irrigation system applied the correct amount of water to an actual tall fescue turfgrass planting whose water needs served as the reference standard treatment comparison for the cool-season turfgrass treatment. Virtual applied water was recorded for other plant materials and it was compared to the corresponding calculated reference standard amount. Results show each controller adjusted its irrigation schedules through the year roughly in concert with weather and ETo changes, but the magnitudes of adjustments were not consistently in proportion to changes in ETo. No product produced highly accurate irrigation schedules consistently for every landscape setting when compared to research-based reference comparison treatments. Greater complexity and technicality of required setup information did not always result in more accurate, water-conserving irrigation schedules. Use of a weather-sensing controller does not assure landscape water conservation or acceptable landscape plant performance, and it does not eliminate human interaction in landscape irrigation management.

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Donald R. Hodel, Peter J. Beaudoin, A. James Downer and Dennis R. Pittenger

In a study in southern California, five species of palms [king palm (Archontophoenix cunninghamiana), mediterranean fan palm (Chamaerops humilis), queen palm (Syagrus romanzoffiana), windmill palm (Trachycarpus fortunei), california fan palm (Washingtonia filifera)] grown in 1-gal containers were planted in 12 × 12 × 12-inch holes in sandy loam (five species) and in clay loam (two species) with the backfill amended using a commercially available, composted, nitrogen-stabilized douglas fir (Pseudotsuga menziesii) shavings product incorporated at 0%, 25%, and 50% by volume. After 18 months, all palms were fully established. Crown volume, stem diameter, visual quality, quantity of new leaves produced, and percent total nitrogen, potassium, and magnesium in leaves did not differ significantly among the three treatments for all species or among treatments within a species. Thus, in this study there was no benefit from amending the backfill with this type of organic amendment when planting palms.

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Dennis R. Pittenger, A. James Downer, Donald R. Hodel and Maren Mochizuki

The responses of five landscape palm species [king palm (Archontophoenix cunninghamiana), mediterranean fan palm (Chamaerops humilis), queen palm (Syagrus romanzoffiana), chinese windmill palm (Trachycarpus fortunei), and california fan palm (Washingtonia filifera)] to three levels of irrigation [50%, 25%, and 0% (no irrigation) of reference evapotranspiration] were evaluated in a coastal mediterranean climate in Irvine, CA. Cumulative leaf production varied greatly among the species, but only king and chinese windmill palms produced more leaves with additional irrigation. All species maintained at least minimally acceptable visual quality at the no-irrigation treatment. Mediterranean fan and california fan palms expressed near optimum performance with no irrigation. Many established landscape palms can maintain at least minimally acceptable appearance for an extended period with little or no supplemental water in coastal mediterranean climates. However, when rainfall plus irrigation is less than 50% of reference evapotranspiration, sensitive landscape palms could be expected to appear less attractive and grow less. Responses of palm species in this study were similar to those of many other landscape tree and shrub species, but the water needs of landscape palms are considerably less than those of commercial date palm (Phoenix dactylifera), oil palm (Elaeis guineensis), or coconut palm (Cocos nucifera).

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Dennis R. Pittenger, David A. Shaw, Donald R. Hodel and William E. Richie

The performance of six landscape groundcover species was evaluated when irrigated at 30% of ET0 at irrigation schedules of three times per week, once per week, once every 2 weeks, and once every 4 weeks. Potentilla tabernaemontani could not be sustained under any of the treatments. For the other species (Baccharis pilularis, Drosanthemum hispidum, Vinca major, Osteospermum fruticosum, and Hedera helix) there were no season-long differences in a species' performance or density due to irrigation frequency, but there were significant differences among species across irrigation treatments. Drosanthemum and Osteospermum provided good overall appearance and density consistently through the season. Baccharis maintained acceptable performance most of the irrigation season, while Vinca and Hedera became unacceptable in appearance in mid-season. Soil moisture content differed among species, but was not consistently different between irrigation treatments.