Garden Detective

Garden Detective: Bentgrass has her over barrel

Bentgrass is a popular grass for golf course’s putting greens, but can be problematical in residential lawns.
Bentgrass is a popular grass for golf course’s putting greens, but can be problematical in residential lawns. Associated Press file

Q: Can you identify this grass or weed? It has a long stem and stolon, very fine blades on the top and it is invading my lawn, which is mostly fescue and rye grass. Is there any selective weed herbicide to control its growth? I am pulling it out by hand; it has shallow roots unlike the bermudagrass.

Teresa Mendick, Carmichael

According to UC master gardener June Bleile, the grass sample that you submitted for identification is bentgrass (Agrostis stolonifera), a cool season perennial grass that spreads by stolons and seeds.

Bentgrass forms puffy, dense patches that may eventually dominate a lawn turf, such as your fescue. Often used by golf courses, bentgrass is great for a putting green where it can be frequently mowed to a half-inch tall, frequently fertilized and receives much water.

However, in a fescue lawn with only weekly mowings and an inch (or less) of irrigation a week, bentgrass turns into a weed.

There is no selective herbicide for bentgrass that will not kill your fescue and rye grass at the same time. If your yard is very heavily infested, there is a chance that if the existing lawn is removed and reseeded or resodded that dormant bentgrass seeds will germinate. And you’re back at square one.

Improving your cultural practices can improve the condition of the lawn without starting over with new seed or sod. Good culture practices include setting the lawn mower to at least 3 inches high, even better at 4 inches, so taller and healthier grass can crowd out weeds and shorter bentgrass.

Also, water deeply at wide intervals. To prevent run-off when deeply watering, set your timer for numerous short cycles for each station, allowing the water to soak in before the point of run-off.

Not wilt, but alkaline soil

Reader Ernie Bullock recognized a familiar problem when he saw the photo of Mary Lowe’s sick redbud.

“Like your reader Mary Lowe of Roseville, I also own an Eastern Redbud tree,” Bullock wrote. “My specimen was planted about 15 years ago and has a 5-inch diameter trunk, and is 20-plus feet high. I used to have some of M.L.’s symptoms, too. Now, my tree is in great health since I started acidifying the soil around it, starting about five years ago.

“What struck me first was the ‘shot hole’ around the leaf margins and inter-venial areas – a symptom often associated with excess boron,” Bullock said of the photo of Lowe’s sick tree. “Further, the yellow-mottled inter-venial areas resemble iron — or possibly zinc — deficiency.”

Bullock compared photos of Lowe’s redbud with examples in “Western Fertilizer Handbook,” published in 1975 by the California Fertilizer Association.

He also noted studies of how pH affects the availability of plant nutrients, such as iron and zinc. “(It’s hard for plants to absorb (these nutrients) when the pH is greater than 7.0, a common occurrence in California soils.

“I would suggest M.L. try applying Ironrite (available at most nurseries or garden centers), or used coffee grounds, to the soil surface under the tree’s drip-zone,” Bullock added. “Both are effective soil acidifiers and will not damage the tree if over-applied. I have blueberry bushes planted under my redbud, and production from these bushes more than doubled once I started regularly using the coffee grounds of two adult coffee drinkers around the bushes. And the redbud above greened up nicely, too.

“Finally, in many local areas, the well water is ‘too high’ in boron – so M.L should test her well water if the ‘shot hole’ problem does not go away after trying these other suggestions. All redbuds in our hot-dry summers need deep irrigation to their root zone every two weeks or they will get nutrient-stressed and ragged looking. After you water, use a shovel to dig down into the root zone – you’ll want to see newly-wet soil down to 2-plus feet a few hours after your water. This kind of deep-watering often takes 4 to 6 hours, or more, on a hose set to low-flow. And move the hose around the trunk every two hours or so.”


Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h& Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

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