With winter around the corner, many gardeners will be preparing their landscape plants for the coming cold temperatures. With an estimated 1 million urban trees worldwide dying each year from freezing temperatures, researchers are trying to find ways we can better protect plants. A study in England suggests that fertilizing in fall with calcium nitrate can help trees survive both freezing temperatures and salt damage from products used to de-ice roads and walkways.
Researchers broadcast calcium nitrate fertilizer around three-year-old evergreen oaks ( Quercus ilex ) and hollies (Ilex aquifolium) at the rate of 4, 8, and 16 pounds per 1000 square feet during the month of October. They picked off the leaves at intervals of 1, 2, 4, and 8 months after the fertilizer application, and tested them for their physiological response to low temperatures and high salt levels. Leaves from trees that received 8 pounds of fertilizer were significantly more tolerant of low temperatures and high salt levels than the control or other treatments. Lower amounts of fertilizer didn't enhance cold tolerance, and the higher amount (16 pounds) damaged the foliage. This research coincides with earlier research that showed similar results when applying calcium fertilizer to deciduous fruit trees and landscape trees.