Why are the bottom of trees painted white in Mexico?

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I recently started travelling through the Yucatán Peninsula in Mexico, through old colonial towns like Valladolid, Mérida and Campeche, and noticed lots of trees painted white at the base and up to about one metre high. At first I thought it was some sort of decoration in the colonial towns, but then I started to notice the same thing on farms and out in the countryside. I was also curious whether the constant painting could damage a tree’s bark. It turns out the white band is doing a specific job, one you find in orchards and on streets around the world, with a bit of local tradition in Mexico on top.

Why do they paint the bottom of trees white?

The short answer is protection, and it is concentrated on the bottom of the trunk for a reason. The lower section of a tree is the part most exposed to direct sun, reflected heat from the ground, and insects climbing up from the soil. Painting the first metre white shields exactly the stretch that takes the most punishment. A healthy trunk keeps the whole tree healthy; when bark cracks and splits, it usually means something is wrong inside, whether that is insects, disease, or sun damage.

The Mexican “cal” tradition and leafcutter ants

In Mexico, farmers traditionally use calcium hydroxide, known locally as “cal”, to whitewash the bottom of trees, especially fruit trees. Part of the reason is a certain kind of ant. Leafcutter ants of the genus Atta are among the most destructive insects to plants in tropical and subtropical parts of the Americas, and they can be devastating to citrus groves. They strip leaves to feed a fungus they farm underground, and a busy colony can defoliate a fruit tree quickly. Cal is strongly alkaline, and the local tradition holds that ants and other crawling insects avoid climbing over it, so the painted band acts as a barrier around the trunk.

White paint protects the trunk from sun damage

The other big reason is the sun. According to the University of California IPM program, applying white paint to trunks reflects light and reduces bark heating, which helps avoid sunburn, and wood-boring pests are frequently a problem on trees where the trunk has been sunburned. This is why the bottom of the trunk gets the treatment: it is the part left most exposed once lower branches are gone, and thin-barked young trees are especially at risk. The white band buys the tree protection while its bark toughens up.

Why trees are painted white around the world

The white band you see in Mexico is one version of a practice used in orchards, on streets and across farms in many countries. Away from Mexico, a few reasons come up again and again.

Sunscald in cold-winter climates

In places with cold winters and strong low sun, the main reason is sunscald. On a bright winter day the bark on the sun-facing side of a trunk warms up while the shaded side stays cold. When the temperature drops again at night, the warmed tissue can freeze and die, leaving cracks that let in disease and insects. A coat of white reflects the low sun and holds the bark closer to an even temperature, so the freeze-and-thaw cycle is less likely to split it, and young, thin-barked trees are the most at risk.

Borers, machinery and marking young trees

White trunks also tend to see less damage from wood-boring insects, since the same University of California IPM guidance notes that borers are frequently drawn to trees whose bark has been sunburned. The paint has two non-biological uses as well: in working orchards a bright band shows mower and tractor operators where a young trunk is, and on new street trees or replanting sites it makes a young tree easier to see so it is not knocked or cut before its bark has toughened up.

Does painting trees white actually work?

For sunscald, the case is reasonably clear. On young fruit trees in climates with strong winter sun and cold nights, a white trunk measurably steadies the bark temperature and lowers the chance of splitting. For insects the picture is more mixed: white paint seems to cut egg-laying by some borers but not all, so it works best as part of a wider pest-management routine rather than a fix on its own. In mild, cloudy places the benefit is slight, so it is far more common in Mexico, the Mediterranean and the drier United States than in northern Europe.

Which trees are painted, and where

The trees that get the treatment are mostly the vulnerable ones: fruit and nut trees such as apple, peach, citrus and almond, young transplants still settling in, and street trees in hot, reflective city conditions. Where you see it depends on the local problem it solves.

• Mexico, the Mediterranean and Southern Europe: lime-washed trunks on citrus, olive and almond, part pest control and part long-standing roadside tradition.
• Drier parts of the United States: sunscald protection on young orchard and street trees under strong winter sun.
• Tropical regions: less about sunscald, more about marking trees and deterring insects.
• Northern Europe: rarely needed, used mainly as a visual marker or against particular borers.

Use water-based latex paint, not oil, and time it right

If you want to try it, the paint matters. The University of California IPM program recommends white interior latex paint, diluted with an equal part of water, because water-based paint is safer for the tree than oil-based paint, which can suffocate the bark. In Mexico the traditional lime wash does the same job while letting the trunk breathe.

Timing matters too. In cold-winter regions the best time to paint is late autumn, after the leaves drop but before the hardest cold, so the coat is dry before the late-winter sunscald season, which falls around April and May in the southern hemisphere. Paint from ground level to the first main branch, or roughly 60 to 90 cm on a larger trunk, and refresh it every year or two.

Frequently Asked Questions

Why are the bottom of trees painted white in Mexico?

Mexican farmers whitewash the lower trunk with lime, or “cal”, to protect fruit trees. The white band reflects the sun to prevent sunscald and, by tradition, deters ants and other insects from climbing the trunk.

Why is only the bottom of the trunk painted?

The lower trunk is the most exposed and most vulnerable part of the tree. It takes the most direct and reflected sun and is the route insects use to climb up from the soil, so protection is concentrated on the first metre.

Why are trees painted white in different countries?

Because the paint solves a different problem in each place. In Mexico and around the Mediterranean it protects citrus and other fruit trees from sun and climbing insects. In the drier United States it guards young trunks against winter sunscald. In tropical regions it is used more for marking trees and deterring borers, and in northern Europe it is rarely needed.

Does painting the bottom of a tree white harm it?

Not if you use the right paint. Water-based interior latex diluted with water, or a traditional lime wash, is safe and lets the bark breathe. Oil-based paint should be avoided because it can suffocate the trunk.

When should you paint a tree trunk white?

In cold-winter climates, late autumn is the usual time, after leaf fall and before the coldest weather, so the paint is dry before the late-winter sunscald period. Cover the trunk from the ground to the first main branch, or about 60 to 90 cm on a larger tree, and reapply every one to two years.