Q. All of a sudden, the leaves of my Japanese maple tree shriveled up and turned black. What happened?
A. There are several species of landscape plants that suffered greatly from frost/freeze damage about two weeks ago. In this case, temperatures dipped in the high 20s and a brisk wind made the problem worse. Japanese maples are particularly sensitive to spring frosts and freezes.
This year, the early warm spring weather pushed tender growth on some plant species that was especially susceptible to cold damage.
Plants that have been damaged by frost and freeze first exhibit water-soaked tissue because the ice that forms within the plant cells pierces the cell walls. The fluids within the cells leak out, causing the watery appearance. The leaves eventually turn brown to black as the water evaporates. Sometimes the leaves will take on a tattered appearance as the leaf tissue dies, and the wind blows away the dead tissue. In some cases the leaves merely became curled or deformed because the frost only damages some of the developing tissue. The damaged tissue never develops but there are other cells that develop normally – hence the curled or distorted appearance. This year many hostas were damaged slightly by the frost or freeze and exhibited this deformed growth.
The new growth of yews was also damaged or killed by the event. Many yews had just begun to pop new growth, which was zapped by the cold weather.
In this case, one observes healthy old growth with blasted new growth on the top and sides.
Shrub roses such as Nearly Wild also took a hit. The new growth was curled or was killed by the cold weather.
Location plays a big role in cold damage. Plants exposed to wind took a bigger hit than plants protected by other plants or structures. In general, Japanese maples should not be planted in area where they are exposed to west or northwest winter or early spring winds. Cut-leafed varieties of Japanese maple are especially venerable. Plant these maples in an alcove, on the east side of the home or places where they are protected from the west winds by evergreen plants.
Normally, plants in lower portions of the landscape are more vulnerable to frost/freeze damage. This was not the case in this event. It appears that most damage occurred between the 3-foot and 6-foot level. This might have occurred because the soil was warm enough to moderate the temperatures nearer the soil level.
The flower buds of hydrangeas and rhododendrons also might have been damaged – along with grapes and peaches. Only time will tell if we see reduced flowering or fruiting of these plants.
Most, if not all, plants will recover from this event. Any dead or damaged growth can be pruned away. Apply a root stimulator and mulch around the plant with an inch or two of quality compost. By mid-June, the plants should be fully recovered.