Why do people paint their trees white?
Is it a rural fable? A picket fence prank? Or, is there real science behind the idea of painting tree trunks white?
It ends up, there are very good reasons for painting both the trunk and the upper sides of exposed branches with a certain type of white paint to protect against sunburn, pests, and disease.
Benefits of whitewashing
An annual application of whitewash reduces sunburn damage by reflecting sunlight away from the tree. Sunburned bark frequently splits and curls, providing easy access for numerous pests and diseases. This is especially true for borers, such as shot hole borers and flathead borers, as well as moth larvae, beetles, and horntails. Whitewashing has also been found to discourage rodents, such as voles, mice, and rabbits, from gnawing on the trunk. The paint also helps protect against frost damage.
What type of paint should be used?
Whitewashing is one of those ‘too much of a good thing is a bad thing’ situations. Using enamel (the wrong paint) can kill young trees. So can using latex (the right paint) if it is undiluted. Traditionally, whitewash was made from slaked lime and chalk. It was a poor man’s paint that tended to rub off onto your clothing if you brushed against it. While this material has mild antibacterial properties, mixing it can be messy.
When you head to the paint store, or go digging around in your garage, make sure that you only use interior latex, and not enamel or exterior latex. Exterior paint may contain harmful additives. The important thing to look for is the "VOC" - these letters stand for "volatile organic compounds". These compounds can be dangerous to trees and humans. Paints listed as being VOC-free or being low in VOCs are better choices, health-wise.
Whitewashing should only be done with interior latex paint that has been diluted with water. Use a mixture of half water and half interior latex paint.
How much of a tree should you paint?
Newly planted bare root trees should be painted completely. To protect mature trees, pull the soil away from the trunk to a depth of 2 inches and paint the entire surface to a height of 2 to 4 feet, depending on the tree. After the paint has dried, put the soil back in place. The upper surfaces of branches that are exposed to sunlight should also be painted.
When should I whitewash my trees?
Here in San Jose, California, whitewash is applied after dormant pruning and dormant oil spraying are complete. This is usually in January or February, but you can whitewash your trees at any time that will allow the paint to dry. After it has dried, you can give your trees added protection from crawling pests with a sticky barrier.
The paint and the sticky barrier will need to be reapplied each year, to maintain their usefulness.
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