black spots in "grass"/ clay

A few of us on our street have "black clay spots" where grass doesn't grow or grows quite thin.
Someone recomended a lime based product which would cure this.
What is the black "stuff" and anyone ever heard of the lime treatment being suggested?
These are new construction houses/ new lawns. Would you do the lime treatment before or after planting grass (too late, grass is already planted, but feel free to answer), before or after starter fertilzer and is this going to be a recurring problem?
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jIM wrote:

That sounds like mold. I suggest contacting your local county extension service, a government agency in the US, although other countries often have like services. They know the local area and are not motivated by profit. They may recommend a soil test, which would be a good idea before apply lime or any soil agent.
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Joseph Meehan

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Is it being watered alot, very hot, everyone is using fertiliser, its stressed and diseased, mold fungus or whatever it is. Mine went away when I just stopped fertilising and frequent watering. But im no lawn expert. If its real hot now where you are everything is over stressed
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jIM wrote:

The only thing lime does is raise the soil's pH. If the problem isn't pH-related (most likely not, since most of the lawn is doing fine, right?) applying lime won't help, and might hurt, if you apply enough to adversely change the pH.

There's all kinds of possibilities, including slime molds or some other type of fungus caused by patches of organic material in the soil decaying (not uncommon in new developments where some construction debris can end up buried). Your best bet is to contact your county's extension agent and present a fresh sample, or take it to your local Master Gardeners, or university, or a reputable local lawn/garden store, if there is one in your area. At the very least, post as good a photo as you can get of it online, then post the link here.

Lime is an old-fashioned 'treatment' for a variety of lawn problems, including mushrooms. It doesn't accomplish anything except change the soil pH, which is almost certainly not your problem.

I wouldn't do it before consulting with a local who can give you a better evaluation of what your problem is, and whether you need to do anything about it.

Again, without knowing what the problem is (or if it's even a problem, not just a temporary anomaly), it's impossible to give useful advice besides 'consult a knowledgable local'.
HellT
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