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What causes lawn mushrooms?

Friday - 6/24/2011, 11:21am  ET

Deep water lawns once a week in summer

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Mushrooms in the lawn

Kent in Alexandria writes, "Mushrooms are taking over my lawn. I keep pulling them for fear the dog will eat them, but they are relentless. The yard is otherwise healthy, fed and managed as per your advice. Is there something pet-friendly I can apply to stop the mushrooms? I'd like to get them before they spread even further."

Well, there are two potential causes of mushrooms in a lawn. One of the most common is underground wood, like tree roots left in the soil or buried construction debris. One reason I always advise people to pay for removal of the stump and roots when a tree comes down is that, if you don't, mushrooms will appear in the grass above the dead roots for a decade or more.

The other common cause of lawn 'shrooms is overwatering. When you have to water the lawn, only water deeply and infrequently, so that the lawn has time to dry out between waterings. Frequent watering virtually guarantees that the 'shrooms will continue to appear, because the spores are ubiquitous in the environment.

If your lawn has serious drainage problems, the mushrooms will be a part of your life until the drainage is corrected, either by the installation of a rain garden or drain tiles.

Don't worry about the dog. These lawn mushrooms are harmless little fungi. Don't try and pull the mushrooms up. That just spreads their fungal spores faster. They're not a real problem. Oddly, having these mushrooms growing in your turf actually improves the vigor of a lawn.

For more info on 'lawn shrooms' (and why some of them are considered to be signs of good luck, visit this full length article by yours truly on Gardens Alive

'Red thread' is often a sign of a hungry turf

Brian in Woodbridge writes, "I'm in my third year of top dressing with compost in the fall and using corn gluten as my spring weed and feed, and my yard has never looked better. But around this time every year, the turf develops brown circles containing pink "threads." This has been diagnosed as the fungal disease red thread. I seem to be unable to prevent its return each year. Any advice?"

'Red thread' is a common disease of cool-season lawns and is worst in cool, wet weather, so the upcoming flamethrower summer should chase it for the season. Then this fall, feed with a composted horse or poultry manure or more corn gluten instead of basic compost. Often, feeding the lawn a little more nitrogen can keep this problem at bay.

Correct watering will save this sod

Joanne in Arlington writes, "We had our yard ripped up in the fall, and installed sod and an irrigation system. It looks beautiful right now, but we would like to know how to properly water our lawn so we can enjoy it for years to come. Our irrigation system is currently set for 20 minutes per zone, three times a week. Shouldn't it be watered more frequently in all this heat?"

No, Joanne. What you want most is for your still relatively new sod to develop deep roots, and the only way to do that is with long, infrequent waterings. Your current short sprinkles are actually stunting the roots and making your lawn more vulnerable during droughts. Try to reset the system to water for several hours at a time, no more than twice a week; and not at all when we've had adequate rain.

Don't sow grass seed in summer

Susan in Springfield writes, "The school I work for is going to reseed our field and I would like to have them water it correctly. You advise watering deeply and infrequently, like from 4 a.m. to 8 a.m. and then not again for a week, correct? Please help. We want to reseed this summer."

Well, not if summer means July or the first half of August, Sue. Spend the summer tilling up what's there, have lots of compost added, level it out, and then spread the seed toward the end of August. No straw or other nonsense, just rake the seed in.

Mist it gently every morning until the new grass sprouts and then gradually back off (mist every other day, then every third day…) until, yes, you're giving the turf a deep watering once a week when we don't get an inch of rain.

Then you can move up to deep waterings twice a week if we don't get rain during the hottest days of next summer, when your new turf will face its toughest test.

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