Each snowfall brings many visitors to the Arnold Arboretum, drawn to the landscape as a beautiful haven for skiing, sledding, snowshoeing, snowboarding, as well as walking and running. As soon as the snow begins to fall, our staff is mobilized to clear snow and keep our roads passable. On these snowy days, visitors occasionally ask why we don’t use deicing salts to clear interior Arboretum roads. The short answer is that concern for the long-term health of our plants and the soil they grow in requires employing different approaches than those used outside our gates.
Salt Contamination and Plants
The rock salt used on city streets excels in removing snow and ice. However, resulting saltwater runoff can also harm plants, especially trees and shrubs. When plows push through ice melt and snow, the salty spray lands directly on branches, stems, and buds. It also coats evergreen leaves and needles. The drying saltwater then desiccates porous surfaces. This damages developing leaf and flower buds, causing poor development or die back in the summer. A coating of salt water can also kill evergreen foliage unless it is washed off.
Saltwater runoff in high concentrations also damages soils. The sodium and chloride within salt water displace potassium and phosphorous, nutrients essential for plant health. During the growing season, some species that absorb high quantities of these minerals essentially die from salt poisoning. Altered mineral composition can increase soil compaction as well, reducing water infiltration and future availability for plant uptake. Of course, many plant species thrive in salty conditions. This is why some coastal species now grow along Massachusetts’ heavily salted inland highways.
Keeping Roads Safe
Unfortunately, some of our most salt-sensitive species grow around or nearby shaded, slippery roads. These include hemlocks, crabapples, white pines, and larches. We reduce slipperiness in these areas by liberally applying sand after each storm and every morning after. Arboretum staff do use deicing salt around entrances, parking areas, and buildings for public and staff safety. In these cases, we follow best practices by using only as much as needed and by consistently monitoring for future applications.
Arboretum staff work tremendously hard keeping the grounds accessible, even on weekends and holidays, regardless of the weather. Remaining open year round for public enjoyment is an essential part of our mission. However, if you think we missed a spot that is a safety concern, please let someone know. Call the Arboretum Ambassador at 857-268-3185 or flag down a staff member. This will help us safeguard both our valued visitors and valued plants, even during Boston’s slippery winter weather.