When to aerate your lawn in Ottawa

Most of Ottawa sits on heavy clay, and clay compacts hard: snow load all winter, saturated spring melt, then foot traffic all summer. Aeration relieves that compaction by pulling plugs out of the soil - but the benefit depends on the grass being in an active growing phase when you do it, because the recovery is where the payoff happens.

Cool-season grasses (which is essentially every Ottawa lawn) grow hard in spring, go semi-dormant through July heat, then surge again from late August until the ground cools. Aerate during a surge and the lawn heals fast and thickens. Aerate in the July lull and you have opened a few thousand holes right when weeds, not grass, are best placed to fill them.

Early April: usually too early. The ground is still saturated from melt. Aerating waterlogged clay smears the hole walls instead of fracturing them. Let it drain first.

Late April to early June: the spring window. Soil is moist but no longer soaked, roots are moving, and the lawn has the whole season ahead. Good choice if your lawn struggles with spring puddling or you missed fall.

Mid June to late August: skip it. Heat stress plus open holes equals crabgrass opportunity.

Late August to mid October: the fall window, and the better one. The fall growth surge repairs the lawn quickly, weed pressure is fading, and the holes are the best seed bed you will get all year if you overseed. Aim to be done by mid October so roots establish before the ground cools.

After mid October: too late. Root growth slows too much for the lawn to take advantage before freeze-up.

• The screwdriver test. If you cannot push a screwdriver into the lawn with one hand, the soil is compacted enough to benefit - and if you cannot push it in at all, the soil is also too dry to aerate well. Water first.
• Moist, not soaked. The tines should pull clean plugs 2 to 3 inches long. Bone-dry clay bounces the tines; soaked clay smears.
• Puddles and runoff after normal rain are the classic compaction signs, along with thin grass on the walking routes across the yard.

• New sod or seed in the last two months - the roots have not set, and aerating tears them up.
• Drought-stressed lawn - wait for recovery rain or water deeply the day before.
• Irrigation systems - do not skip aeration, but mark the sprinkler heads visibly first. That is what actually prevents a strike.