WIRE BASKETS-CURRENT PRODUCTS AND THEIR HANDLING AT PLANTING

Journal of Arboriculture, Jul 2004 by Appleton, Bonnie, Floyd, Scharlene A

The first wire baskets used were made from nongalvanized steel, and it was assumed that within a few years they would rust away and pose no potential hazards. According to Watson and Himelick (1997), wire baskets can last up to 30 years below ground. This articles senior author excavated numerous wire baskets during spring and summer 2003. Many of the baskets, known to be in the ground from 15 to 18 years, were still completely intact and, though corroded, the basket wire was very difficult to break.

Lumis (1990) reported that wire strength diminishes very slowly below ground. Tensile strength of 9-gauge, galvanized and nongalvanized wire was tested on baskets that had been planted for 4 years. Over the 48 cm (19.2 in.) depth of the baskets, tensile strength of the galvanized wire, which transitioned from slightly discolored to slightly corroded with depth, decreased only 5%. Nongalvanized wire, which was moderately corroded over its entire depth, decreased in tensile strength by only 3%. Lumis stated that these, and similar tests performed on wire that had been in soil for longer time periods, indicated that significant corrosion does not occur rapidly as a result of either less oxygen or more moisture at various soil depths.

While Carpenter (1987) reported that many thousands of trees had been planted in wire baskets with very few reports of problems, Watson and Himelick (1997) stated that tops of buttress or flare roots generally grow into the upper horizontal basket wires, causing partial girdling of roots and restricting vascular flow (xylem water and nutrient transport up, and phloem carbohydrate transport down). Whitcomb (1987) reported root restrictions and injury to roots of several trees planted in painted, but not galvanized, wire baskets that had been in the ground for 6 years and that showed little signs of deterioration except near the soil surface.

Research to date addressing the vascular flow part of this controversy has been limited. In 1988, Lumis and Struger reported that large structural roots of approximately 11year-old golden willow (Salix alba 'Trista') had deeply embedded wire beyond which, after 1 to 2 years, a complete union of vascular tissue had formed despite initial infolding of periderm tissue. Lumis (1990) reported the same observations with other tree species, but noted that these observations did not confirm the anatomical or functional integrity of the vascular tissue. These observations were in contrast to those of Feucht (1986), who stated that root vascular tissue does not rejoin after growing around wire.

In research with 2-year-old green ash (Fraxinus pennsylvanica) and hackberry (Cellis occidentalis) and 2-year-old whips of a hybrid poplar (Populus angulata � plantierensis), Goodwin and Lumis (1992) reported none of the trees whose roots were girdled with wire had grown any less than those with nongirdled roots after 6 months. They did report, however, that full girdling significantly reduced foliage dry weight in ash. The rate of transpiration in ash and hackberry was significantly reduced, and a gradient of water potential was observed across the wire girdle in the xylem. Root tissue carbohydrate level, and its distribution in relation to the wire, was slightly influenced by girdling in all three species. They concluded that although this research did not answer the question of whether wire baskets should be removed at planting, they felt that compared to the stresses that occur due to significant root loss at harvest for field-dug trees, the effect of roots growing over wire baskets would be limited.