Tree Whitewashing: Why Are Tree Trunks Painted White?

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During a stroll in the countryside, you might have spotted an orchard with tree trunks painted white. This method, a natural alternative to pesticides for fruit trees, is called limewashing. It involves applying lime milk to tree trunks as a preventive measure against pests and diseases.

What is whitewashing for trees?

Limewashing means applying lime to tree, especially fruit trees trunks (or even ornamental trees).

You could of course use quicklime directly, but a preparation based on lime called lime milk, or more commonly tree whitening, is recommended as it’s less corrosive and dangerous.

This whitewash is made of powdered lime crust (a by-product of the thermal decomposition of limestone) mixed with water. It is a natural alternative to the use of chemical pesticides. Long used by previous generations, it’s making a comeback today due to its (almost) zero environmental impact. It can be used in organic farming.

Why apply lime to trees?

Limewashing fruit trees isn’t for aesthetic purposes as some might think! It’s primarily a preventive treatment against the ravages of certain insects or fungi, which are the main causes of fungal diseases. To put it simply, limewashing a tree helps sanitize it and protects it from the proliferation of parasites and diseases.

So, tree whitening is effective against:

• Insects hibernating in fruit tree bark. Practically, lime milk has an insecticide action as it kills the eggs and larvae of insects like codling moths, aphids…
• Cryptogamic diseases caused by the presence of fungi in bark crevices. Lime milk is effective against moniliosis (mainly affecting apple and peach trees), scab, peach leaf curl, canker in fruit trees, shot hole disease… It has an antifungal action
• High temperatures and severe frosts. Lime milk provides protection against scorching sun rays and frost that can damage young tree trunks and graft points. Tree whitening regulates temperature fluctuations
• Lichens and mosses, whose expansion is limited by tree whitening

What limewashing actually protects against

Limewashing is not applied for looks: each coat of lime milk works on a different trunk problem. The table below sums up what the article says the treatment acts on, and how.

The same treatment does have limits, which are set out further down the page.

Tree trunk whitewashing steps

Whitewashing trees involves several steps, starting with prep work for your trees.

When to apply it, and how often?

You can apply lime paint between September and April, but late winter is best because it’s a time when nature is waking up thanks to rising temperatures, especially bugs and fungal spores.

A February or March application works best. Make sure to put tree paint on trunks during a frost-free day, with no announced rain and no wind.

Tree whitewashing should be performed every 3 to 4 years.

Where to apply whitewash?

Lather lime paint onto tree trunks, from the ground to the base of primary branches. Bark should be perfectly dry before application.

How to apply limewash?

Before smearing tree trunks with lime paint, it’s key to prepare trees by scratching the bark first with a hard-bristle brush. This step helps eliminate moss and lichen, as well as dead bark pieces. After that, follow these steps strictly to avoid any risks:

• Wear tall gloves, boots, and goggles
• Get your lime-based paint ready in a metal bucket by strictly following package instructions
• Apply the mix using a flat brush, starting from higher up, focusing on crevices of fruit trees. One layer may be enough but you can apply two if your fruit tree has a lot of crevices. The paint itself can be stored for about 4 months.

Downsides you shouldn’t ignore

While whitewashing provides clear benefits, it also has a few negative consequences you should know about:

• It doesn’t really distinguish between pest insects and beneficial insects. So, it can wipe out helpful insects that maintain biodiversity, at least those that also find shelter in tree bark
• It has no effect on insects and spores overwintering in the ground or on higher branches
• It may worsen tree wounds because lime milk can penetrate tissues

Want to learn more? Check these out:

• Organic treatments for fruit trees
• Fruit trees: choosing, planting, pruning, and fruit harvesting
• Moniliosis and fruit rot: tips and treatment