Spring is the best time to dethatch your lawn
CORVALLIS – Thatch, a layer of living and dead grass stems and roots, is the natural consequence of a healthy lawn, according to Tom Cook, turfgrass specialist with the Oregon State University Extension Service. It becomes a problem only if you let it get too thick.
“Dethatching a lawn is best done each spring,” said Cook. “When you dethatch annually, you don’t generate a big load of debris. But if you let it go for too many years, removing thatch can become a long, agonizing process.”
The right amount of thatch provides a soft surface for bare feet and makes the lawn more resilient to wear and tear. But with too much thatch, water, air, and nutrients will not be able to penetrate below the lawn into the soil. Too much thatch makes a lawn too dense. It may be green on top, but it is brown and dead-looking underneath. When such a lawn is mowed, the brown thatch layer is often exposed, and the lawn looks “scalped.”
How do you tell if your lawn needs dethatching?
“If your lawn is soft or spongy, or you have dry spots despite regular watering, then it needs some work,” says Cook. “If only the very top part of the grass plant is green, and the rest is brown, or you scalp your lawn when you are mowing, then, you need to dethatch.”
Regular dethatching removes brown stems and forces buds to grow near the base of the grass stems, preventing the grass plants from being brown underneath and green only on top. Dethatching followed by fertilizer stimulates new grass shoots to grow in thick and lush.
For best results, dethatch your lawn every year or two. Bentgrass lawns, the most common type in the Willamette Valley, are best maintained with an annual dethatching, between late March and mid-July. In central and eastern Oregon, Cook recommends annual dethatching just as the grass starts to turn green, generally in April. Dethatching at this time will also remove moss from lawns and get your lawn off to a flying start for the growing season.
The easiest way to dethatch is to rent a dethatcher. The flail-type dethatcher is the most common machine found at rental yards. Thatching rakes work well, with the addition of lots of elbow grease, but Cook does not recommend the small dethatchers sold as lawn mower attachments because they beat up the lawn mower.
If you rent a dethatcher, first adjust the blades on a paved surface so they are about one inch above the surface of the pavement. If the blades are set too low, they may tear up the lawn and remove entire chunks of sod. Make between one to five passes through your lawn, until most thatch is removed. Always fertilize the lawn with a nitrogen-based fertilizer after removing thatch. The added nutrients will stimulate growth and help the thinned out turf to fill in.
Dethatching an average-sized lawn every year or two will yield one to three pick-up loads of thatch. The thatch can be composted or used for mulch if it is herbicide-free. If you have used a weed killer or “weed and feed” treatment in the month before dethatching, do not use it to make compost or mulch.