I don't think saw dust would be a problem in general. In fact, I think it would help ... So long as it sits in TOP of the soil. Wood in general is a nitrogen hog, but if it's above the soil it will use nitrogen from the air. However, if it gets below the soil it can rob nitrogen from the grass plants.

Saw dust is slow to break down, but I've heard thst once it does, it is one of the best things for your soil. You might try experimenting with some Milorganite or other organic fertilizer in the areas where the sawdust was blown. That would feed the microbes there, and encourage them to break down the sawdust faster.

Some things I would question (and that I'm not qualified to answer) involve these questions: What type of wood? Treated wood? Untreated wood? Logs or boards? Is the dust from sanding or sawing? Did the dust come from wood that was painted, stained, or lacquered? I don't know if these things matter, but I suspect that saw dust created from cutting a log would have a different effect on the lawn than the saw dust created from a treated deck wood that was painted and then covered with a chemical sealant.

I have clay soil, and routinely spread sawdust. While the sawdust does use Nitrogen, it adds organic material to the clay soil. It also absorbs water to help maintain the moisture levels.

There are a couple of don'ts. Don't put a lot of sawdust in any one spot, dust it on the yard. Also if you are using highly treated lumber or certain types of wood known for their toxicity, they would not be good to put on the yard.

I have known people to use sawdust to mulch around trees, though it has been a while and I do not remember the outcome.

Way back when I made the mistake of building a swing set and tree house for my daughters out of treated wood which I sawed out in the yard. That grass died and the spot became bare no matter how much compost I piled on it. My girls are in college now and that spot where I sawed the wood is still bare. If there is any chance you have treated wood dust out there, I would suggest you dig up the top several inches and replace it with new topsoil or sand.

Otherwise untreated wood should be fine. Over on the soils forum there was a guy who made cabinets. He dumped the cabinetry dust in his garden and essentially reclaimed his bad soil. Untreated sawdust on top of the soil is a good thing.

I put down hundreds of pounds of sawdust pellets (untreated) last summer to help with soil structure down the road. No problems to report.

+everybody above. Treated wood can certainly be a major problem, or amounts so large that the grass can't get air or sunlight.

However, I've dropped thousands of pounds of sawdust (untreated pine) as topdress and never seen any negative effects. Just don't dig it in or the grass will get yellow and unhappy.

The sawdust would have been from oak, poplar, maybe a little bit of walnut. All boards, and probably from sanding, sawing, etcs. I don't think i've cut any treated wood, or at least not that I can remember.

So in the dead areas, where i've pulled up some of the dead St Augustine i'm starting to get weed growth... is that maybe a sign that the soil is NOT damaged? Would weeds still grow if sawdust was the issues?

Weeds will grow where conditions will favor their growth. Likewise, Turf will grow where conditions favor it. The conditions for one are not always the same conditions as the other. It really depends on the type of weed you are talking about and also the type of turf.

Rather than going down that route (if weeds are growing will turf?) it would probably be easier to just analyze the conditions of the soil. A soil test can be performed and that will provide you with the current conditions. From there, you can amend as necessary to improve the soil for turf.

That being said, you mentioned your St Augustine is dormant. It's winter so I would expect the turf to have some weed pressure until the spring and summer?

mdo, what's your watering regimen? How often and for how long do you water?

Rotting wood attracts fungus & st augustine is very prone to fungal attacks. Chemical antifungal effectiveness is 50/50 at best. That said, there is a LOT of anecdotal evidence saying 'sawdust is good for soil'.

I was thinking the same things reeljake. Really it could be coincidence that the sawdust is getting spread over the same area that's being overwatered.

Not the sawdust