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Mulching 101: How to Mulch Your Trees the Right Way

by Admin on
Arborist Tips Gardening Soil Amendment
Mulching is one of the simplest and most effective ways to care for your trees. When done correctly, it helps retain soil moisture, suppress weeds, and improve overall soil health. 

Too"mulch"of a good thing?

Mulch helps trees, but placement matters. Piled against the trunk, it holds moisture against the bark. And while research on very deep layers is mixed, we keep our own mulch to 2 to 3 inches, so that is what we recommend.

In this article, we’ll share expert mulching tips and best practices to ensure your trees thrive. Whether you’re prepping for winter or enhancing your garden year-round, these guidelines will help you avoid common mulching mistakes.

Not all mulch is created equal. Mulch includes any material used to cover soil, while wood chips are coarser and often made from freshly chipped trees. Wood chips work well for established trees but may not suit young plants or gardens needing finer textures.

  • Arborist mulch is local, high nitrogen mix of woody and plant debris derived from local tree service chipping
  • Leaf mold mulch is made through anoxic fungal decomposition
  • dyed black mulch is dyed with natural carbon but also may contain creosote or other concerning preservatives
  • dyed red mulch is coloured with iron oxide but also may contain creosote or other concerning preservatives
  • Detailed view of wood chippings in a pile

Avoid dyed mulches from garden supply stores. These often contain recycled wood from pallets or treated lumber, which can introduce harmful chemicals. The dyes can also leach into the soil, affecting plant health. Opt for organic, untreated mulch, leaf mould or composted wood chips for safer, more effective results.

Mulching in 3-Simple-Steps

Before adding mulch, inspect the area around your trees and plants.

  • Ensure the soil has adequate drainage to prevent water-logging.
  • Check for nearby plants that might be affected by the type of mulch or the mulching process. e.g. avoid acidifying the soil with a pine mulch and go with hardwood if your plants prefer a more neutral pH.

Organic mulches are ideal because they enhance soil health as they break down. Options include:

  • Composted Wood Chips or Leaf Mould: a composted mix that includes leaves, bark, and wood is highly effective and enhances soil quality. Check out Monty Don's excellent leaf mould how-to video
  • Fresh Wood Chips: Suitable for established trees and shrubs.
  • Other Organic and Green Mulches: Arborist mulch containing shredded leaves, branches, bark and twigs or other mulch mixes with pine needles or straw are unconventional looking but work as an organic fertilizer by infusing nitrogen back into the soil to enhance growth.

Avoid using inorganic materials like rocks or rubber mulch, as they do not provide the same soil-enhancing benefits.

Proper mulching means spreading mulch in a wide, donut-shaped ring that extends out to the tree’s dripline (the edge of the canopy).

Mulch should be no more than 2 to 3 inches (5 to 7.5 cm) deep and must be kept away from the trunk. The tree’s root flare should remain visible and uncovered.

Avoid “mulch volcanos” caused by piling mulch against the base of the tree, this holds moisture against the bark and buries the root flare.

 (Below) Improper vs. Proper Mulching TechniqueProper mulch technique - colour highres with text

  

Root collar area
(Left) Root Collar Area

Identification of the root collar (aka trunk or root flare) on a tree is critical.

Mulch should be kept about 4 to 8 inches back from the collar, and further back on large mature trees, and should never cover the flare. This lets the base of the trunk dry out and exchange gases through its bark. Constantly damp bark is more open to decay and disease.

Mulching: 3 mistakes to avoid

  1. Over-Mulching: Going much deeper than 3 inches (7.5 cm). Deeper mulch suppresses weeds better, but research on tree health at greater depths is mixed, and a deeper pile makes it easier to bury the root flare.
  2. Improper Placement: Mulch that touches the main portion of the tree trunk or root flare holds moisture against the bark and makes it harder to inspect the base of the tree.
  3. Ignoring Existing Layers: Failing to rake or remove old mulch can result in compaction and reduced soil oxygen. Putting  down landscaping fabric on dry soil and piling mulch on top may exacerbate soils that have become hydrophobic because water runs off the fabric and is unable to penetrate the dry substrate.

By avoiding these pitfalls, you’ll ensure your trees get the full benefits of mulching without the downsides.

 

Why mulching matters for tree health

At Arbutus Tree Service, we recommend mulching as a key component of tree care. Whether you’re maintaining your landscape year-round or getting ready for winter, proper mulching can help your trees thrive in Vancouver’s unique climate.

If you have questions about mulching or tree care, our experts are here to help. Contact us today to schedule a consultation or learn more about our tree care services.

What the research says: In a two-year study of young pines and oaks, Greenly and Rakow (1995) found the most new stem growth under 3 inches of mulch, while deeper layers suppressed weeds better without helping the trees more. A 2026 review of 11 mulch-depth studies (Martin et al.) found the evidence inconclusive on the depth at which mulch starts to harm trees, with problems mostly reported beyond 4 inches. Either way, we recommend 2 to 3 inches, kept clear of the trunk.

For more on this topic, check out Proper Mulch Technique (pdf guide) from Trees are Good.

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