Well, according to the website, for $20-38/ sample, my county agricultural extension is happy to give me a soil analysis and recommendations. They say it takes a couple of weeks. That seems helpful.
I guess the part that puzzles me is the bit that adding in more organic material is “an expensive guess” … to me that is no regret move.
The previous lawn did fine even competing with the oak tree for water and nutrients. Now there is backfill that has stones in it. Almost for sure less ability for that lower organic material rich backfill to hold water or to supply nutrients. Now competing with the tree is too much, especially when trying to establish new plants. There is less “sponge” there now.
No matter what the test result a part of the response will be add more organic material into the top soil. More carrying capacity. Yes if the pH is way out of line then something more also to offset it, but in reasonably off ranges organic material will buffer just fine, either way, right?
I’m not wondering about the test not being worth doing. It is cheap and might guide which plants to use? But ISTM that there is no result that means adding decent quality organic material is an incorrect or unnecessary response.
The extension service website does say that some soil has too much organic material, and lists some of the problems that can cause. (And they list recommended amounts for various crops, including lawn grass.) But I’m quite certain this patch of ground doesn’t suffer from too much organic matter.
That being said, if it suffers from too much of some salt, for instance, it’s probably easier to “rinse out” the excess before adding the organic matter I’m sure i need.
Taking that literally - is that possible?
If you have a choice of sources of organic matter, it may also make a difference to your choice.
If your state has a Master Gardener program (likely through their university ag extension), ask them about what NATIVE plants would do well in your area, and plant those. Possibly this is an opportunity disguised as a problem. Go native with the entire area and do a few things at once: Lower the water demands, because natives have evolved to use the water that nature provides in your area (subject to climate change, of course). Native pollinators love native gardens, and create a more diverse biome. You’ll also probably have to do less work to maintain it, too.
Again, if you have too much of a particular nutrient, adding organic material might not help and possibly cause additional harm. It’s very likely that the backfill used doesn’t have too much of one, but you won’t know until you test it. The test is cheap and doesn’t involve much work, better to do it first.
I get plenty of rain for fine fescues, at least in the shade. I never water the lawn except when I’ve just put down seed, which i don’t do very often. And i have a large number of native pollinators, because i plant (or don’t pull out) a wide variety of flowering plants. For instance, i get some vetch in the back yard flower bed. In theory, it’s a weed. But it has pretty purple flowers that the bees enjoy at a time in the summer there’s not a lot else in bloom.
But that’s an interesting question. What are our native ground covers? (I’m on granite in the North East.)
The extension website suggests it as the way to deal with certain excesses. It says, “it might take 2”-4"of water to do this". That doesn’t actually seem like an enormous amount of water.
Sounds to me like you’re already doing a lot of natives! Maybe just let that ground sit and see what comes up? I have no idea what a native ground cover would be for you…maybe rock? 
Yes, excesses of various nutrients and salts will leach out of substrates if you add enough water.
Adding organic matter will tend to slow this down- that’s one of the reasons for adding it, it holds nutrients and stops them washing away so easily.
I dug up a soil sample, which is now drying, in preparation for mailing it off, and I’m really glad i did.
First, the grass is doing a lot better than i realized. It must have grown after the fall rains, or maybe i just haven’t been paying attention. Not cutting it was a win, because the soft blades fall down and cover a lot of the soil. So it mostly looks green. And in between grass i mostly have dense moss, which is fine.
But the soil! The soil is so much better than i expected. Two years of clover (even though it died the second year) and a year of grass, and three years of picking up all the pebbles that i noticed coming up have made an enormous difference. It was hard to get the sample, because almost everywhere i stuck my trowel, the soil was full of roots. And the actual soil feels like dirt, not like “fill”. I only removed a few stones from my pile of dirt.
I also took a walk today, and looked at everyone else’s trees and lawns. Most of the maples and pines have a dead (or mulched) patch around them, but few of the oaks do. I was amused by one lawn that was “lush bluegrass turf” except right next to a large maple, where it had nice dense fine fescues. So i wasn’t just lucky, i think i can expect to grow lawn right up to my trees. And while there are a lot of lush, well-tended lawns, there’s are plenty that look like what I’m aiming for, too. I’m not going to embarrass my neighbors.
I’ll send the sample off in the mail on Monday, and hopefully get results in a week or two.
Thanks, everyone.
You’ve been leaving all the mowings on the lawn, right?
There’s some of your organic matter right there.
I haven’t actually mown it more than once or twice a season. But of course. Mulching lawn mowers are awesome.