When to trim hedges in Ontario

A hedge that is cut twice a year on fixed dates will look tidy and gradually get sparser. A hedge cut according to what the plant is doing will fill in year after year. The difference is timing, not effort.

The general rule

Trim after a flush of new growth has hardened off, not while it is soft and actively extending. Cutting soft growth wastes the energy the plant just spent and often triggers another weak flush that will not harden before frost.

In the GTA that usually means a first trim in June, once spring growth has firmed up, and a second in late August or early September.

The last trim of the year should be early enough that new growth has time to harden before the first frost.

The cedar rule that matters most

Cedars, which are everywhere in Mississauga, will not regenerate from old wood. Cut back into the bare brown interior and that section stays bare permanently. There is no recovery and no product that fixes it.

This means a cedar hedge has to be kept in shape continuously. Once it is badly overgrown, bringing it back inside its intended line means cutting into dead wood, and at that point the honest options are living with a larger hedge or replacing it.

Shape: wider at the bottom

The single most common mistake is trimming a hedge with vertical or inward-sloping sides. That shades the base, the lower branches thin out, and within a few years you have a hedge that is dense on top and see-through at knee height.

Angle the sides slightly so the base is wider than the top. Sunlight reaches the bottom, the lower growth stays dense, and the hedge screens properly.

Flowering shrubs are different

• Spring bloomers set buds the previous year, so trim right after flowering
• Summer bloomers flower on new wood, so trim in late winter or early spring
• Get it backwards and you remove the flower buds before they open
• This is the most common reason a shrub stops flowering after someone trims it