Piet Stoker (PhD)
Frost protection for trees
Winter is upon us! A single cold spell can cause your newly planted trees to either die off to the ground, or damage its cell structure inhibiting future growth. This blog explains our best practice for protecting your trees from frost and cold damage.
We start with a few important facts.
Black frost is a term used for very severe frost which usually occurs during clear sky, wind-still nights. Cells in the tree's leaves (and possibly in its trunk and branches) freeze, causing them to burst. Green leaves die overnight and turns black in a day or two. The tree dies off to ground level. It may sprout from ground level in the next season (since its roots are still intact). However you have lost a few years worth of growth and also the tree's growth form.
When there is no wind, cold air descends to ground level. Hence it is coldest just above ground level
Cold winds, usually from the south, cause cells in the tree's bark to freeze, usually on the side from where the wind blows. The part of the trunk not exposed to such a cold wind may survive. The tree's growth will slow down but it is likely to survive and retain its canopy height.
Some trees are more frost resistant than others, because their cells contain one or more chemical substances which lower the cell's freezing point. It acts like the anti-freeze that you put in your car's radiator. See our blog "Fast growing indigenous trees"
Create a protective air layer around the tree's trunk.
In our experience reed grass is an ideal material to protect your trees from frost.
Air is an excellent isolator. The idea is to create an air layer between the tree's trunk and the outside air.
Reed grass is used for thatch roof construction. Most pole suppliers stock reed grass in bundles as seen on the photo. It is a convenient material and not expensive.
Use one or more bundles depending on the trunk diameter of your tree.
Arrange reed grass evenly around the trunk
Loosely tie one or more bundles around tree BEFORE cutting the ropes with which the individual bundles are tied. (See picture)
Arrange the reed grass evenly around the tree's trunk. Ensure that it covers the trunk all around, at about the same thickness. Then tie it down firmly around the trunk at three or so places. IMPORTANT: ensure that reed grass is packed all the way down and into the soil. (Remember coldest air is just above ground level)
If the tree's trunk exceed the length of the bundle, tie a second set of bundles higher up. Cover the thunk all the way to the point where the tree branches. In a worst case cold scenario, the tree's canopy branches may die off, but it will re-grow during the next season from about the same height. Consequently you will retain the height which the tree has already accomplished.
Wrap reed grass with a wind shielding layer
Finally wrap the reed grass with a wind shielding layer. We use cling wrap for this purpose. The idea is to prevent cold winds to blow through the reed grass thereby securing a protective air layer around the trunk.
Wind/air can not penetrate glad wrap. This may cause the trunk to sweat. We therefor recommend that you remove it as soon as the cold season is over.
Alternatively wrap reed grass with a less dense material that will allow breathing, for example flannel, polar fleece or a few layers of freeze cloth.
Finally tie the wrapping material as shown in the photo