Why Are Trees Painted White at the Bottom?

Trees are painted white at the bottom to protect them from sunscald, a form of bark damage caused by extreme temperature swings during winter and early spring. On a bright, cold day, the sun-facing side of a dark trunk can heat up enough to wake dormant cells beneath the bark, only for a sudden drop in temperature after sunset to kill them. White paint reflects sunlight and keeps bark temperatures far more stable, and research in stone fruit orchards has measured temperature reductions of up to 30°F on painted trunks compared with bare ones. The practice is centuries old, looks oddly cosmetic, and is more scientifically grounded than most people assume.

How Sunscald Damages a Tree

Sunscald goes by several names, including “southwest injury,” because in the Northern Hemisphere the south and southwest faces of a trunk absorb the most direct winter sun. On a clear winter afternoon, bark on that side can climb well above freezing while air temperature stays far below it. Researchers have recorded differences as large as 25°C between the north and south sides of the same trunk.¹ That warm patch tricks the living tissue just beneath the bark, the cambium, into breaking dormancy. When the sun drops behind a cloud or the horizon, the bark surface temperature crashes. The newly active cells, caught off guard, freeze and die.

The visible result is a patch of dead, sunken, or cracked bark on the sunlit side of the trunk. Over time the damaged area can split open, inviting fungi, bacteria, and boring insects into the heartwood. In fruit trees, sunscald wounds shorten productive life. In landscape and street trees, they create structural weak points that can lead to branch failure or whole-tree decline years later. The damage is cumulative: a minor crack one winter becomes a deep canker the next.

What the White Paint Actually Does

Dark bark absorbs solar radiation efficiently. White paint reflects much of it. The effect on surface temperature is dramatic. A study on stone fruit trees in midlatitude orchards found that painting the sun-facing side with white exterior latex paint reduced bark temperature by roughly 30°C compared with unpainted trunks during midwinter conditions.² That same research noted the cooling benefit grew even larger on thicker trunks and on calm days when wind was not already carrying heat away. A separate Michigan orchard trial confirmed that on sunny winter afternoons, white latex paint kept the south side of trunks about 15 to 30°F cooler than untreated controls.³

By keeping daytime bark temperatures closer to ambient air temperature, white paint prevents the warm-then-freeze cycle that kills cambium cells. It does not insulate the tree or keep it warmer at night. Its entire purpose is to stop the trunk from overheating during the day so that the subsequent nighttime drop is not lethal.

Does the Specific Color Matter

You might expect any light color to work and any dark color to make things worse. The broad principle holds: lighter surfaces reflect more solar energy. But the research picture has a wrinkle. A 2024 study examining different-colored tree pastes found that paste color played a smaller role in bark surface temperature than expected, with the authors concluding that the assumption about white preventing significant temperature swings “seems irrelevant.”⁴ That finding sits in tension with the older orchard studies showing large temperature differences between painted and unpainted bark. One likely explanation is methodology and formulation. The paste products tested in the 2024 study may have had similar thermal properties regardless of pigment, while the earlier work compared clean white latex paint against completely bare, dark bark. The baseline matters: a white coating on a very dark trunk creates a bigger contrast than comparing two different-colored paste products that both cover the bark.

Meanwhile, infrared thermography work on arboricultural materials found that white-painted bark and other light-colored treatments consistently stayed cooler than untreated bark, while black burlap wraps showed no temperature benefit at all.⁵ On balance, white remains the standard recommendation because the temperature evidence in its favor is strongest and most consistent. If you use a commercially tinted tree paste, though, the protection may still be adequate depending on the product’s formulation and how it interacts with the bark surface.

Which Trees Benefit Most

Not every tree in a landscape needs painting. The ones most vulnerable to sunscald share a few characteristics:

• Thin bark: Young trees and smooth-barked species like cherries, maples, beeches, lindens, and aspens lack the corky insulation of deeply furrowed bark. Their cambium sits closer to the surface and heats up faster.
• Recent transplants: A tree that spent years in a nursery row surrounded by neighbors suddenly stands alone in an open lawn. The south and southwest sides of its trunk, previously shaded by adjacent trees, are now fully exposed to winter sun.
• Fruit trees: Orchard species like peaches, plums, cherries, and apples are classic sunscald victims. Commercial growers have painted trunks white for generations because the economic cost of losing a producing tree to bark injury is real.
• South-facing exposures: A tree on the north side of a building, shaded all winter, is at far less risk than the same species standing alone on a south-facing slope.

Mature trees with thick, deeply ridged bark, such as old oaks or black walnuts, rarely need painting. Their bark is already a built-in insulator that buffers temperature swings. The exception is any mature tree that has recently been heavily pruned or had neighboring shade trees removed, suddenly exposing trunk surfaces that were previously shielded.

What Kind of Paint to Use

The standard recommendation is plain white interior or exterior latex paint diluted with water, typically mixed at about a one-to-one ratio so it goes on thin and does not completely seal the bark. Full-strength paint works too, but diluting it allows gas exchange through the bark’s natural pores. The Michigan orchard trials specifically found good-quality outdoor white latex paint to be the most practical sunscald prevention among the treatments tested.³

A few things to avoid: oil-based paints can damage bark by clogging lenticels, the tiny pores through which a tree breathes. Paints with fungicides or other biocide additives are unnecessary and can introduce chemicals into the tree’s tissue. Bright-white, high-titanium-dioxide exterior paints give the best reflectance, but even a cheap flat white interior latex will do the job. Some growers use commercial tree-trunk paint products, which are essentially pre-mixed white latex with added wetting agents. They work fine but cost more than a gallon of hardware-store paint.

Apply paint from just above the soil line up to the first major scaffold branches. In fruit orchards, that usually means the bottom two to three feet. You only need to coat the south and southwest sides if you are being precise, but wrapping all the way around is common because it is faster and offers protection even as sun angles shift between autumn and spring. Application in late autumn, before the first hard freezes, gives the best protection. A single coat typically lasts one growing season before it weathers and flakes off, so it is an annual task for trees that need it.

Alternatives to White Paint

Paint is not the only option. Tree wraps, sometimes called trunk guards, are spiraling strips of paper or plastic designed to shade the bark surface. Light-colored wraps can reduce bark temperatures meaningfully, but the material matters. The infrared thermography study that tested multiple products found that white burlap wraps kept bark up to about 4.5°C cooler than bare bark throughout the day, while black burlap wraps provided no measurable cooling at all.⁵ Translucent commercial tree protectors, the rigid plastic tubes sometimes placed around young nursery trees, also showed no temperature benefit in that study. Their value is more about physical protection from rodents and mowers than thermal regulation.

Wraps have a practical downside that paint avoids: if left on too long into the growing season, they can trap moisture against the bark and create a hospitable environment for fungal infections and bark-boring insects. The standard advice is to apply wraps in late fall and remove them in spring after the last hard freeze. Paint, by contrast, just weathers off on its own and does not create a moisture trap.

In home landscapes, some people position a board or stake on the southwest side of a young tree to cast shade on the trunk during the critical afternoon hours. It is low-tech and effective, though not especially attractive. Planting trees where buildings or evergreen hedges provide afternoon shade eliminates the problem entirely for that particular exposure.

When White Paint Is About More Than Temperature

In some parts of the world, especially the Mediterranean, Latin America, and Southeast Asia, you see rows of street trees and orchard trees painted white up to about waist height. The practice there goes beyond sunscald prevention. In warmer climates where freezing is not the issue, white-painted trunks serve as a deterrent to certain bark-boring insects and, in some traditions, as a highly visible marker along roadsides to help drivers see the edges of tree-lined roads at night. The lime wash used in many of these regions is a simpler preparation than latex paint, just hydrated lime mixed with water, and it also raises surface pH enough to discourage some fungal growth on the bark surface.

Lime wash is the historical ancestor of modern trunk painting. Before latex paint existed, orchardists mixed calcium hydroxide with water and sometimes added copper sulfate, producing a preparation called Bordeaux mixture, which doubled as a fungicide. That tradition persists in many regions, though latex paint has largely replaced lime wash in commercial orchards in North America and northern Europe because it lasts longer, sticks better, and gives more consistent reflectance.

Potential Side Effects of Lime-Based Coatings

One concern that rarely comes up in gardening guides is what happens when calcium-rich coatings wash off the trunk and into the soil below. Rain carries dissolved calcium carbonate downward over time. Research on white oaks growing near calcium carbonate surfaces, such as concrete parking lots and roadways, has documented that alkaline runoff raised soil pH to the point where manganese became chemically locked up and unavailable to roots. The affected trees developed manganese deficiency, with foliage testing well below normal levels.⁶ That study dealt with runoff from large paved surfaces rather than from painted trunks, so the scale of the calcium input was much greater. Still, the mechanism is worth knowing: if you are using lime wash rather than latex paint, and especially if your soil is already neutral to alkaline, repeated annual application over many years could nudge the root zone pH upward. Latex paint does not have the same chemistry and is unlikely to cause the same issue.

For most backyard fruit trees, the amount of lime reaching the soil from a single painted trunk is small enough that it is not a practical concern. The risk is more relevant in large orchard settings where hundreds of trunks are treated with lime wash year after year, or in landscapes where the native soil already has limited manganese availability. If you are unsure about your soil, a standard soil test will tell you your pH and whether micronutrient availability might be at risk.

Why the Practice Looks Strange but Works

People who encounter rows of white-painted trees for the first time often assume it is decorative, or that someone got carried away with a bucket of paint. The visual result is admittedly conspicuous. But the practice exists because it solves a real problem cheaply. A gallon of white latex paint costs a few dollars and protects dozens of young trees for an entire winter. Replacing a dead fruit tree, waiting several years for it to reach bearing age, and losing that production in the interim costs far more. In municipal forestry, where newly planted street trees represent a significant per-tree investment, painting or wrapping trunks is standard practice in many regions precisely because the cost of losing transplants to sunscald is high relative to the cost of prevention.

The one scenario where painting does not make sense is on mature, thick-barked trees in their established locations. An old oak or hickory with deeply furrowed bark is already well insulated against temperature swings. Painting it would be cosmetic at best and mildly counterproductive if the paint interferes with gas exchange through the bark. Reserve the brush for the trees that actually need it: young transplants, thin-barked species, and fruit trees exposed to direct winter sun on their south and southwest sides.