Our Northwest

Is your lawn still growing like it's spring?

Friday, November 11, 2016by  Jon Osterberg

man mowing lawnI just came in from mowing my lawn for the second time in four days. This is crazy.

Typically, in November my lawn grows so slowly that I mow it every week or 10 days, with my final mowing of the season happening on Apple Cup weekend. (That used to be the third November weekend, but now UW and WSU battle on Thanksgiving weekend.)

I've assumed all along that sunlight stimulates lawn growth, with temperature playing a lesser role. Northwest lawns stop growing once it freezes, and that happens in short-daylight months.

But after scouring credible online sources like the master gardeners at WSU Extension and Oregon State University Extension, Better Homes and Gardens, and my Sunset Western Garden Book, I've learned that temperature plays perhaps the largest role in lawn growth and dormancy.

As you likely noticed, it's been warm this week around Puget Sound. Like record-setting warm, 72 degrees in Redmond on Tuesday, and in the mid-60s for several days before that.

No wonder I'm mowing as if it's May. Around here, those are May temperatures!

Among the facts I've learned about Northwest lawns (which by the way are typically a blend of fescues, ryegrass, and bluegrass that like our mild climate):

  • Grass doesn't stop growing in the winter, but it slows so much it's barely visible, especially below 40 degrees.

  • Why does it slow? Grass needs warm air and soil to metabolize carbon dioxide, water, and sunlight.

  • fall leaf in grassGrass contains lots of water that could freeze in winter, so it hardens itself by increasing the concentration of salts within its cells.

  • Just as Northwest lawns decline in the cold, growth also slows above 80 degrees. During hot, dry periods, lawns may need mowing just once every two or three weeks.

If any of this is related to global warming, mowing may eventually become all-season exercise for me. That's not necessarily a bad thing.

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