How much mulch, and when
Mulch is the cheapest thing you can do for a garden bed, and the easiest to overdo.
A properly mulched bed holds moisture, suppresses most weed germination, moderates soil temperature and looks finished. A badly mulched bed does none of that and can quietly kill a tree over several years.
Depth: five to seven centimetres, no more
Two to three inches is the working range. Thinner than that and light reaches the soil, so weeds germinate anyway. Thicker and you create a layer that sheds water instead of letting it through, and that stays wet enough underneath to rot stems.
Most beds do not need a full refresh every year. Fluffing the existing layer and topping up the thin spots is usually enough, and it is cheaper.
Mulch is a blanket, not a burial.
The mistake that kills trees
Mulch piled against the trunk in a cone — sometimes called volcano mulching — is common and genuinely damaging. Bark that stays permanently damp begins to rot, and the tree grows roots up into the mulch instead of down into soil. Those roots then circle the trunk and slowly strangle it.
Pull mulch back a good ten centimetres from every trunk and stem. The flare where the trunk widens into the roots should be visible.
When to do it
- Late spring, once the soil has warmed, is the main application
- Mulching too early on cold clay keeps the soil cold and slows everything down
- A light autumn top-up helps beds hold their line through winter
- Never mulch over weeds you have not removed, it delays them rather than stopping them
Type
Shredded bark or wood chip for most GTA beds. It knits together, stays put on a slope, and breaks down into the soil over a couple of seasons, which is a feature rather than a problem — that decomposition is what improves the clay underneath.
Dyed mulches hold colour longer and add less to the soil. Rubber mulch adds nothing at all and never breaks down. For a garden that is supposed to improve over time, organic is the better choice.