Trees are often the unwilling recipients of proclamations of love, notifications, for sale advertisements and tagging. Most of these activities are relatively harmless to tree health unless there is a significant amount of physical damage to sensitive plant tissue. Fortunately, most of these items can be removed without much problem.

However, paint and other chemical applications can cause additional damage. Paint may clog the tiny openings on trees called lenticels, preventing gas exchange such as CO₂ produced by respiration getting out and O₂ needed for respiration getting into the tree. Also the paint may interfere with photoreceptors embedded in the stem. When these sensors are covered, it interferes with the tree’s ability to sense changes in light quality, intensity and duration which can disrupt normal plant processes. In addition, the bark and cambium layer can be damaged by absorption of the chemical properties in paints. These paint chemicals, especially those found in oil-based paints, can cause severe damage and even death on thin-barked trees.

The removal process of the paints on trees can create quite a headache in the corrective actions. However, it can be successful with careful work and consideration for the absorptive properties of the tree.

Try to remove graffiti as soon as possible after it is applied. Prompt removal reduces the damage to the tree as most paint products have harmful petroleum distillates and other oil properties in them. Use citrus-based graffiti removal agents that contain ingredients such as “natural orange extract.” Citrus-based degreasers are essentially the same as graffiti removal agents and are more readily available at local retailers. Citrus-based products are mostly biodegradable; they contain very few, if any, hazardous substances, and they rinse clean with water. These degreasers do very little harm to trees. Always read the precautionary statements listed on a product label before using any product.

After applying a citrus-based removal agent, it is usually best to allow the remover to penetrate the graffiti message for a variable amount of time, depending mostly on the length of time the graffiti has remained on the surface. For example, newly applied graffiti can be sprayed with a removal agent and rinsed with satisfactory results in 20 minutes. Graffiti that has been applied for several weeks or months will require the removal agent to sit on the surface for 1-2 hours. Best results are usually achieved by at least two applications of the removal agent before rinsing.

Use a hose with a high-pressure nozzle or better; use a pressure washer to rinse and remove graffiti that has been treated with a removal agent. Be sure to use the pressure washer carefully on tree trunks, especially thin, smooth barked trees to avoid any damage to the tree. High pressure spray can damage the bark and vital tree components if applied intensely in one area. When using a high pressure hose nozzle instead of a pressure washer, it may be helpful to agitate the treated graffiti with a stiff nylon or plastic brush to improve removal efforts. Wire brushes can be damaging to the tree without careful use.

Remember to be gentle and reduce damage to the tree trunk. If the removal process is unsuccessful at first, multiple applications over time may be required. Sometimes a simple, creative aerosol paint combination can be used to cover or disguise the tagging efforts if on a small scale. Be natural and use long, vertical spray strokes to match the tree color as best as possible. Water-based paints are not as harmful as oil-based covers. This is always the last course of action.

Good luck and hopefully the tree can be restored to its natural appearance.​

Resources:
Graffiti Removal From Trees, The Education Store, Purdue Extension’s resource center
Find an Arborist website, Trees are Good, International Society of Arboriculture (ISA)
Caring for storm-damaged trees/How to Acidify Soil in the Yard, In the Grow, Purdue Extension
Moist soil and rotten roots makes it easy for trees to come crashing down, Fox 59 News
Why Is My Tree Dying?, The Education Store
Tree Risk Management, The Education Store
Mechanical Damage to Trees: Mowing and Maintenance Equipment, The Education Store
Construction and Trees: Guidelines for Protection, The Education Store
Trees and Electric Lines, The Education Store

Urban Forestry, Purdue Extension