Why Your Mulching Mower Leaves Clumps and How to Fix It

You’ve got a 1.5-acre lawn, a Toro LX420 with a 42-inch deck, and a beautiful, thick stand of grass thanks to a wet spring and extra fertilization. The problem? Every pass leaves a trail of mulched clippings, forcing you to mow two or three times to get a clean look.

Follow the One-Third Rule

Never remove more than one-third of the grass blade in a single mowing. If you maintain a 4-inch height, don’t let the grass exceed 6 inches. Under vigorous growth conditions, that may mean mowing every five days.

Check Deck Design and Baffles

Mulching relies on the deck’s “dome” and internal baffles to keep clippings suspended long enough for the blade to pulverize them. Damaged baffles or a worn deck can cause clumping. Inspect the underside of the deck for dents, missing baffles, or excessive wear.

Mow When Dry

Wet grass doesn’t flow; it clumps. Wait until the dew has evaporated or the lawn has dried after rain before mowing.

When to Consider a New Mower or Kit

If the deck is in good shape, you’re mowing frequently enough, and the grass is dry, but you still get trails, a dedicated mulching kit (high-lift blades, optimized baffles) may help. A new mower is a last resort—your Toro has a solid reputation for mulching when set up correctly.