Arboriculture & Urban Forestry 34(5): September 2008 the fall before the installation, the structures were planted into bare, untilled ground. The site required repeated applications of herbicides and hand weeding throughout the next seasons. The area had bare soil paths that were slippery during and after episodes of rain, and the ground was prone to winter heaving. A turf-covered site was used in the 2007 installation and provided effective and attractive ground cover. The establishment of turf eliminated the need for weed control using herbicides or manual labor and created safe and appealing cover for the site. The maintenance requirement included periodic mowing. It has been previously recommended to cover the planting area for living structures with geotextile fabric or plastic as an alter- native method to minimize the weed competition (Warnes 2004). This practice was not implemented here because of the nonbio- degradable nature of the material and limited aesthetic value. The plantings were installed on 1 to 3 June 2006 and 15 to 17 May 2007. The 2006 plantings grew satisfactorily and were vi- sually appealing. The same design was repeated in the 2007 installation, when the final refinement of the structures was ac- complished with the help of Kim Vergil, an artist from Canada. The design was laid out with paint, and the stems were inserted into pilot holes 30 cm (12 in) deep made with a steel dibble bar. The turf was mowed before painting out the design, and glypho- sate was applied along the contours of the structures 30 cm (12 in) wide. The stems were pushed into the ground to the 30 cm (12 in) depth by applying some pressure without preparing pilot holes. After planting, the stems were thoroughly watered. Plants in both installations received supplemental irrigation only during the first year after the planting and were not subsequently irri- gated. Annual topdressing of shredded bark mulch for weed control at the stems’ bases was applied to inhibit the weed com- petition and preserve moisture. At the end of May and in July, the soil at the base of the structures was fertilized using Lesco Professional Starter Fertilizer (18N–24P–12K; Lesco, Cleve- land, OH). Table 1 provides a timeline for the major operations that were undertaken for the installations and maintenance re- quirements of the living structures. Information recorded throughout the growing seasons in- cluded the installation protocol, materials used and a timeline required for each installation, maintenance requirements, and plant performance, including stem survivability as well as insect and disease pressure. RESULTS AND DISCUSSION Design Attractive designs were critical to the visual appeal of living structures. Two design goals were addressed: the development of Table 1. The major operations undertaken for installation and maintenance of living structures made of willow (Salix) stems. Year Season Activity 0 Fall 1 1 2 2 Site preparation: weed control and lawn installation Spring Planting, mulching, and watering Summer Watering, fertilization, mowing, weaving or pruning in August Spring Fertilization Summer Mowing, pruning once a month in June, July, and August 291 a portfolio of simple modules (individual structures) and the integration of various modules into more complex elements. The individual modules can be used as freestanding elements, may be incorporated into traditional gardens, or integrated into more complex living playgrounds. Although the construction of indi- vidual modules required knowledge of basic techniques and a precise design, their integration allowed for much flexibility and site-specific approaches. A portfolio of modules, ranging from simple arches, wig- wams, and arbors to domes, fences, tunnels, and mazes, was developed (Figure 1). Illustrated instructions designed for an inexperienced individual with detailed steps for the construction process can be accessed online (see “Supplementary Materials”). These forms were selected based on major criteria that included simplicity of construction and low maintenance. The incorpora- tion of the modules into a more complex environment was ac- complished in the blueprint “Children’s Mini-Village” that inte- grated six modules into a single planting design (Figure 2). The combination of various functional structures—centerpieces (dome, arbor) and linear modules (tunnel, fence and maize)— allowed the modules to be linked together thereby increasing the entertainment value of the installation. Species Selection The varieties of willows used for the installations had been pre- viously selected for biomass production in North America. All had exceptional growth characteristics, adaptability to the grow- ing conditions of the northeast, and natural resistance to pests (Tharakan et al. 2005; Labrecque and Teodorescu 2005b). All plants established quickly and performed satisfactorily through- out the period of the study. All varieties foliated in the middle of April and abscised the foliage in the beginning of November. Seasonal changes such as fall leaf coloration were not obvious because foliage remained generally green until abscission. The stems of ‘S × 61’ were less flexible and not suitable for deep bending. A light infestation of Japanese beetle (Popillia ja- ponica) was observed in ‘SV1’ in the beginning of July during both years of study. Two clones—‘S × 64’ and ‘S × 67’— exhibited the required characteristics for stem pliability and rapid growth, retained clean foliage throughout the season, and exhibited no pest problems. Species selection is critical, because not all willows are ap- propriated (Table 2). Basket willow (S. viminalis L.) was not suitable for the northeast region of the United States. Although this species is a “favorite” species for applications in Europe, Canada, and South America (Danks 2002, 2003; Gro 2004; Warnes 2004), it is susceptible to damage by the potato leafhop- per (Empoasca fabae) (Smart et al. 2005). White willow (S. alba L.) and its cultivars ‘Vitellina’ and ‘Britzensis’ have bright mul- ticolored stems but were very susceptible to willow tar spot (Rhytisma salicinum). The disease, manifested by circular ne- crotic regions on the leaves by early August, caused early leaf senescence and drop by the end of August, drastically affecting the visual appeal of the plants. Future species testing should be limited to the subgenus Vetrix, which is characterized by shrub-type growth habit, inde- terminate shoot growth producing several flushes of growth, and good pruning and regrowth response (Kuzovkina et al. 2008). This subgenus has extensive fibrous root system with the majority of fine roots found in the upper 40 to 45 cm (16 to ©2008 International Society of Arboriculture
September 2008
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