In this spring’s notes: a long-standing drainage problem in Longenecker Horticultural Gardens has been resolved, trees and shrubs were damaged by animals and extreme cold this winter, and the conifer collection will be labeled in the coming year.

New Drainage Culvert

The southeast corner of Longenecker Horticultural Gardens (LHG) has long been prone to seasonal flooding, creating what we have dubbed “Lake Longenecker.” It was caused by garden topography coupled with the damming effect of the service road to the south. G. William Longenecker recognized this problem and installed a culvert under the utility road early in the gardens’ development. However, the culvert has since failed and filled in. The flooding traditionally occurred during the late winter and early spring due to snow melt and seasonal rain while the ground is still frozen. As the climate shifts, extreme rain events are more common and the flooding has increased. During 2018, the area flooded six times, resulting in a two-acre area of standing water that persisted for an average of two weeks. This greatly stressed the plants in the area, even causing some mortality, and created ideal conditions for large summer mosquito outbreaks. We have worked with UW–Madison Facilities Planning and Management to remediate the problem, and a new culvert was installed under the service road in late March.

Winter Weather and Plant Damage

This winter, persistent snow cover and extreme, prolonged cold resulted in plant damage throughout the collection. One major cause was hungry animals in search of food. Damage from rodents (including mice and voles) and rabbits was high. Rodents stayed under the snow to avoid predators, and as the population rose and food became scarce, they removed bark around the base of woody plants to eat the nutrient-rich cambial tissue underneath. In some cases, they completely girdled the plant, cutting off nutrient and water flow and ultimately killing it. The snow also covered ground food sources for rabbits while giving them access to feed higher up in the plants, chewing through bark on branches and munching on buds. Deer browse was also more pronounced throughout the collection. As snow made food sources on the ground inaccessible and the cold drove them to consume more calories to stay warm, they turned to nutrient-rich buds as a food source. As a result, many woody horticultural plants were denuded of their terminal branch buds up to the deer browse line (6′ above the ground).

The cold temperatures also damaged plants, though the severity won’t be known until plants break winter dormancy and resume growth. The Arboretum recorded -27°F on January 30, followed by -29°F the next day. These are the lowest temperatures the Arboretum has experienced in 23 years. As a result, we expect to see some die back and even mortality to marginally hardy woody plants, and potential damage is likely to overwintering flower buds on some species within the collection.

Labeling the Conifer Collection

In 2016, we began a multiyear project to label all LHG specimens with easy-to-find and -read 3″x 5″display labels. The conifer collection will be the focus of this year’s labeling efforts. Over the winter, LHG staff compiled, vetted, and created label templates for all 619 specimens currently in the collection. Supported by a generous gift from the American Conifer Society, we purchased anodized aluminum label stock and tools to cut and shape labels to size. The Arboretum has also acquired a laser engraver, which will make label creation timely and cost efficient.

—David Stevens, Longenecker Horticultural Gardens curator