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Tagging Along in Tropical Botanic Gardens - The Experience of the National Tropical Botanical Garden, Hawai'i

Volume 3 Number 1 - December 1998

Melany H. Chapin and Sylvia Smith

Labelling plants with scientific accession tags in a botanic garden is one of the most critical steps for keeping track and maintaining the genetic purity of a botanic collection. It is what links the plant to records of its origin, collector and wild habitat conditions. Botanic garden labelling systems can be subject to neglect or they can be created from materials that cannot withstand the impacts of the climate or gardening practices. If a labelling system breaks down it can result in a drastically de-valued collection, because the link to the plant's origin is lost. All climates have harsh requirements for permanent labels, but the tropics impose even greater challenges especially with salt spray from the ocean, humidity that promotes corrosion of metals and growth of moulds and mildews, and ultraviolet rays from the sun that break down plastics, colouring, and vinyl. Rigorous weeding, both manual and with tools, is required year round which can dislodge labels. Tropical soils can also be full of iron oxides which contribute to corrosion. Labelling systems which have been developed for temperate-climate botanic gardens often weaken or fail under these conditions.

The National Tropical Botanical Garden, located in Hawai'i and Florida has been experimenting with many botanic garden labelling systems since its inception in 1971. I hope this article will help gardens in the tropics avoid the problems that we have had in the National Tropical Botanical Garden and use a system that will last and withstand tropical conditions. We recently modified and adapted some of the practices developed for use in the orchid greenhouse collections at the Marie Selby Botanical Gardens in Florida. Features important to us include a labelling system we can easily customize, has bar-coding ability, generates labels directly from the accessions database, possesses upgradability of the system, and has options for using images. The metal tag also needs to be able to withstand the impacts of weedeaters (strimmers), lawn mowers, regular herbicide treatments, tropical soils and weather conditions. We experimented with a Thermal Transfer Printer and environmentally resistant materials.

In September, 1997 I took sample labels using these materials and put them in sterile containers with the following materials: dry beach sand, wet beach sand, ocean water, tap water, herbicide spray (Roundup 1%, Sarflan, indicator dye, and water) valley soil that is high in iron oxides, and a control that had just air. The containers were kept damp as appropriate. The containers were sealed and left in my office at room temperature for a year. The labels all withstood the insults of each of these conditions and still look like new. Although a test was not conducted with a tag exposed to UV for this study, tags in full, tropical sunlight for at least a one-year period of time have not shown any signs of fading or deterioration. In addition, the printed tags without a clear overlaminate sustained the conditions equally well as the tags with the clear overlaminate and could possibly be used without the extra covering. The overlaminate though, does provide an extra layer of protection from physical trauma such as gardening tools, weedeaters, branches scraping against the tags, and other similar impacts. In addition, over two years of experience has shown that the laminate does not tend to peel off or loose its adhesive properties.

Not only does the label need to be resilient, but the label stake needs to be as durable yet safe. We began using ¾ x 15-18 in (1.2 x 38 cm) iron rebar stakes. These are reinforced steel bars which are used by construction workers with cement for foundations of buildings for structural support. Since the bare rebar could possibly be dangerous to visitors and staff, a PVC cap was designed to cover the top 7 in (18 cm). The PVC cap is a piece of plumbing pipe with a plumbing "cap" glued onto it, then spray painted a dull green or brown to blend into the background. Holes are drilled through the top and at the base. Plastic coated wire (18 gauge) is used to attach the PVC cap to the rebar stake and to attach the label to the cap. This reduces the possibility of corrosion. First you drive in a reinforced steel bar into the ground, then attach a PVC cap which has a tag wired to it. The tag is attached to it by the hole through the top of the cap. The result is a permanent tag and label attached to a stable and permanent stake, both able to withstand most weedeating efforts, and most environmental impacts.

Botanic gardens are not the only application for this labelling system. The United States Fish and Wildlife Service staff have used this system on Kauai, Hawai'i to set up a grid for a restoration project in a mesic forest area at ca. 900 m. It would also be useful for any long-term experiment or research project that required fixed markers in an outdoor environment. These tags can even be used in bog or coastal areas. The true test of any labelling system is time. So far, this system has fulfilled all the requirements we were looking for in a permanent botanic garden label. The experiments with the various soils, water, chemicals, and other environmental conditions prove that for one year, at least, these labels can withstand these impacts. In twenty or thirty years we will have a better understanding of the long term resilience of these materials, and hopefully technology will continue to contribute to advancements that can be adapted by botanic gardens in the tropics and around the world.

Detailed Specification

A Thermal Transfer Printer is a specialized printer for printing directly on rolls of plastic labels for use in nursery pots and/or rolls of adhesive permanent polyester outdoor labels which are printed and then stuck onto either stainless steel or aluminium tags. It has it own software and is connected to a PC. It is useful for high volume in-house tag printing needs and will also print bar codes. The printer costs about US $3,000. Two printing ribbons are required: the lower grade ribbon for printing directly onto plastic tags (cost approx. US $40-60) and higher grade ribbon (wax/resin) is needed for the outdoor labels that adhere to the stainless steel tags (cost approx. US $90). The high grade resin wax ribbon is critical to the success of outdoor tags. The model of printer used has a steel casing so that it is very robust in nursery setting and produces high quality permanent labels.

The plastic tags last about three years, the permanent outdoor tags (that use high quality labels with the wax/resin ribbon) supposedly last "permanently". The labels are a specialized material that is resistant to UV, water, and other outdoor impacts. They are adhesive backed so they just peel off and can be stuck onto the metal tags. We chose a high quality label to withstand the impact of most environmental conditions and silver because we wanted the labels to blend in with the stainless steel tags. The high quality labels come in rolls costing about US $300 for 1000. They come in various sizes (e.g. 3.0 x 1.0 in, 2,75 x 1.25 in) to fit the printer and can be laminated as well. The Marie Selby Botanical Gardens use white labels and the bar codes show up well in a nursery but in a garden, you see patches of white instead of the plants.

The tags we use are made of stainless steel with a flat surface. However in the Marie Selby Botanical Gardens orchid house they use aluminium but it tends to corrode in Hawai'i. We were able to specify the size of tag and the manufacturers made a dye cast but the initial cost was high. The size is 1½ x 3½ in with the hole for the wire centered 1/8 in (on left side of label).

Old labels can be recycled by soaking them for 3 months in liquid WD 40 in a heavy plastic bucket. The adhesives of the labels break down and the stainless steel tags are then easily wiped clean and are ready for new labels.