Whitewash for trees is a protective coating, traditionally made from lime, applied to the trunk and lower branches to shield the bark from environmental stressors. This white layer reflects sunlight, moderating the temperature of the tree’s surface and preventing damage. The practice is widely used by orchardists and home gardeners, particularly on young or thin-barked varieties, to encourage healthy development. This guide details the reasons for applying this coating, where to find the necessary materials, and how to apply them effectively.
The Purpose of Tree Whitewashing
The primary function of whitewashing is to prevent sunscald, which is damage to the bark caused by extreme temperature fluctuations during late winter and early spring. A tree’s dark bark naturally absorbs solar radiation, especially on the south and southwest sides, causing the trunk temperature to rise significantly on sunny winter days. This warmth can prematurely activate the living tissue, or cambium, beneath the bark, causing sap flow to begin.
When the sun sets or a cloud passes, the temperature drops rapidly, freezing the newly activated tissue and causing the bark to crack and split. This damage creates open wounds that leave the tree vulnerable to pests and diseases. The white coating reflects up to 90% of the incoming solar radiation, maintaining a more stable, cooler temperature in the bark and preventing these damaging freeze-thaw cycles.
Beyond thermal protection, the whitewash provides a physical barrier that helps deter certain boring insects and pests. Wood-boring insects are often attracted to volatile compounds released by sun-damaged trees, so preventing the damage removes the initial attractant. The alkalinity of the lime-based wash may also inhibit the growth of fungal and bacterial pathogens on the bark surface. This measure protects the tree’s structural integrity, particularly during the first few years after planting when the bark is thin.
Commercial and DIY Sourcing Options
The most direct way to acquire this material is by purchasing a specialized commercial product, often labeled as “tree trunk paint” or “tree guard.” These products are formulated to be non-toxic and breathable, allowing the bark to exchange gases and moisture normally. They can be found at garden centers, farm supply stores, and large home improvement retailers.
Alternatively, many gardeners opt for a simple, readily available material: white interior latex paint. This type of paint can be diluted with water to a 50:50 ratio before application, making it safer than exterior or oil-based paints which can hinder the bark’s ability to breathe. When choosing a latex paint, ensure it is a plain, non-toxic formula without added fungicides or mildewcides that could be harmful to the tree.
For a traditional, lime-based coating, the primary ingredient is hydrated lime, also known as slaked lime or calcium hydroxide. This material is distinct from agricultural lime, which is used to adjust soil pH, and must not be confused with quicklime (calcium oxide), which is highly caustic and dangerous to handle. Hydrated lime is commonly sold at hardware stores, building supply outlets, or masonry supply companies.
The traditional mixture often includes a binding agent to help the coating adhere to the bark and last longer through rain. Common binders include table salt or a small amount of horticultural oil or interior latex paint. Some recipes also call for the addition of zinc sulfate or copper sulfate, which provide fungicidal properties, sourced from specialty agricultural or chemical suppliers.
Mixing and Application Guidelines
Safety is a primary concern when preparing a lime-based whitewash, as hydrated lime is caustic and can irritate the skin, eyes, and respiratory system. Wear gloves, eye protection, and a dust mask when mixing the dry powder with water. The traditional formula involves slowly adding 10 pounds of hydrated lime to 12 quarts of water in which 3 pounds of salt has been dissolved.
The mixture should be thoroughly stirred until it achieves a smooth consistency similar to a thin, creamy paint that is easy to apply with a brush. If the mixture is too thick, dilute it with more water; if too thin, add more lime. Allowing the mixture to sit overnight helps the lime fully dissolve and thicken, improving adherence to the bark.
The ideal time for application is in late fall or early winter, before the onset of the harshest cold and sunny winter days. Using a paintbrush or a low-pressure sprayer, apply the mixture evenly to the entire circumference of the trunk, starting from the soil line and extending up to the lowest scaffold branches. Ensure full coverage on the side of the trunk facing the afternoon sun (typically the south or southwest side in the Northern Hemisphere).
A second coat may be necessary, especially on rough bark, once the first layer has completely dried. The goal is a uniform white covering that completely obscures the dark bark, maximizing solar reflection. Since the coating will gradually wear off over time, annual reapplication in the fall is a necessary maintenance practice.