Every blade of grass is a small solar panel. Cut it too short and you remove most of the leaf the plant uses to feed itself — so it spends its energy regrowing leaves instead of roots. Shallow roots mean a lawn that browns the moment the weather turns hot.

Taller grass, deeper roots

For the cool-season grasses most Portland lawns are made of — perennial ryegrass, tall fescue and fine fescues — we keep mowers set between 2.5 and 3.5 inches, and a little higher in mid-summer. That extra inch of leaf builds a deeper root system that rides out dry spells.

What short mowing really costs

More weeds

Many weed seeds need light to germinate. A taller canopy shades the soil and stops a lot of them from ever getting started.

More water

Longer blades shade the soil surface, so less moisture evaporates. Scalped lawns dry out faster and need more irrigation to stay green.

Our rule of thumb

Set the deck high, keep blades sharp so they cut instead of tear, and never take more than a third of the blade at once. If your lawn looks great for two days and tired for five, height is usually the reason.