Adding topsoil over tree roots can be done, but it must be approached with caution to avoid harming the tree. Trees exchange gases with the atmosphere through their roots, and significantly altering the soil depth over these roots can reduce gas exchange, leading to stress and potentially harming the tree’s health.

Here are some guidelines if you’re considering adding topsoil over tree roots…

Considerations Before Adding Topsoil Over Tree Roots

• Minimal Depth – If you decide to add topsoil, keep the layer as thin as possible—ideally no more than 2-3 inches (5-7.5 cm). Adding a thick layer of soil can suffocate the roots, leading to root rot and other health problems for the tree.
• Avoid Piling Soil Against the Trunk – Do not pile topsoil against the tree’s trunk. Soil accumulation against the trunk can cause moisture to build up, promoting rot and fungal diseases that can harm or kill the tree.
• Choose Quality Topsoil – Use high-quality, well-draining topsoil to prevent waterlogging, which could further stress the tree. Ensuring the soil has a similar composition to the existing soil can help prevent water from pooling at the interface between the new and old soil layers.

Alternatives to Adding Topsoil

• Mulching – Instead of adding topsoil, consider using mulch around the tree. Mulch can improve soil moisture, regulate soil temperature, and reduce weed competition without significantly impacting gas exchange if applied correctly. Apply a 2-3 inch (5-7.5 cm) layer of mulch around the tree, keeping it away from the trunk to avoid moisture build-up and potential trunk diseases.
• Planting Ground Covers – If the goal is to enhance the aesthetics or control erosion, planting shade-tolerant ground covers around the tree can be a safer alternative. Choose plants that require minimal additional soil disturbance and can coexist with the tree’s root system.

Best Practices

• Consult an Arborist – Before adding topsoil or making significant changes to the landscape around mature trees, consult with a certified arborist. An arborist can assess the potential impact on the tree and offer guidance tailored to your specific situation.
• Monitor Tree Health – After adding topsoil or making any changes, monitor the tree’s health closely for signs of stress, such as leaf yellowing, premature leaf drop, or branch dieback. Early detection of stress can allow for corrective actions to be taken before the tree is irreversibly damaged.

Adding topsoil over tree roots should be done sparingly and with careful consideration of the potential impacts on tree health. Whenever possible, opt for less invasive alternatives to support both the tree’s well-being and your landscaping goals.