I also use oak leaves with no problems....This would be interesting to see. Maybe we would have better results without them? I wonder if it's more of, the tree is a very established tree, and the extensive roots are hogging nutrients?

After a little research, I'm finding that oaks are indeed allelopathic, via the tannins that they produce, but that allopathy is alleged to just affect grasses and herbs. That is, no self-respecting oak is going to worry about poisoning tomatoes underneath that are competing for nutrients! Is there more to it than that?

But maybe oak compost actually does weed suppression? Wouldn't that be nice.

Not clear what is special about herbs. I grow herbs in soil that is amended regularly with oak leaf compost.

That's an interesting idea- weeds. Of course, the homemade compost I used to start my lettuce this year had many weeds sprouting in the seedling trays hahahaha.

The allelopathic effect of many plant and tree species are not persistent once removed from the growing plants. When exposed to the elements, the chemicals responsible break down in about 2 - 3 weeks. At worst, the chems could be throughout a root for example, but as that root decays, and the successive layers are exposed, the chems quickly breakdown. In the case of leaves, the effect of the responsible chems would be EXTREMELY short-lived. You can look up the issue in a websearch. Even juglone, probably the most well known allelopathic offending chem, is only effective for no more than 21 days - the tests are done in what amounts to germinating seeds in petri-dishes in which juglone is present. It's possible that there are longer-lived chems, but I don't know of any.

The reason the research was done was to try to find a natural pre-emergent herbicide. No persistence has yet been found.

That makes sense about the effect being very short-lived in the leaves. My neighbor has a huge red oak, and some of my leaves that I compost are blown over onto my yard from his. But he doesn't rake them up. He just buzzkills them with a mulching mower, and doesn't collect the trimmings. (In fact, down here, hardly anyone collects mower trimmings.) So the red oak leaves end up chopped up and spread out all over his lawn to compost in situ. That lawn, except in a circle around the tree itself, is doing fine. If oak leaves poisoned grass, his whole lawn would be dead.

So, the "circle of death" that we're talking about here is due to allelopathic chemicals from oak roots, I guess.

Now, that all being said, the allelopathic chemicals in oak are allegedly tannins. I guess tannins break down easily? if the breakdown is done by microbes, that would explain why tannins last a long time in red wine, which has no microbes.

Dan - all of the bare ground around my trees are caused by my lawn service(me) tearing up the grass when mowing around them. Sure beats weed eating around them!

Doing a little research, I also see an article that finds that oak leaf tannins actually inhibit lots of fungal growth. I guess that might slow down composting of those leaves. It seems to be well understood that oak leaves don't compost as fast as other tree leaves, and that may be why. To the extent that they don't, it's what makes chopped up oak leaves good mulch.

Could it be that the area closest to the trunk is not only shady but is also the driest spot due to more roots close to the surface and less rain reaching the ground?

There are no live oaks around here, but I never hesitate to add other kinds of oak leaves to my compost pile. I also like to mulch with lawn mower chopped up oak leaves because they do not mat down as much as my other main choice, maples.

I never said it was shady. My largest oak leans significantly, and loads of sun gets under there. By the same token, it's going to be just as wet.

If that particular oak does have allelopathic chems, it would likely, as many other such species, exude it from the roots. There are however, a few other potential causes of a lack of grass there.

You could easily conduct a controlled experiment by trying to germinate a few seeds in a sample of soil taken from the area, and a control taken from an area where grass tends to thrive. Keep the experiment going for about a month, successively germinating new seeds in fresh samples every few days.

If you know of other potential causes, it would be interesting to hear about them. It's not sun or water. There are such rings of death around all the oaks around here and, as I concluded above, it probably isn't in the leaves. So yes, the roots are probably the issue.

Tree roots could be close to the surface so the grass can't get depth for their own roots. Tree could be soaking up most of the water and moisture for itself, leaving little for potential grass. Those issues, combined with a little shade, and a lawnmower constantly whipping the soil around and giving further stress to the already struggling conditions, might just make it inhospitable to grass. Might have been a tree mechanic's spot X-number of years ago for dumping whatever...

There could be any number of reasons we aren't aware.

A neighbor of mine was having similar trouble. Shade was the biggest problem. He kept trying different grasses, reseeding every few weeks... etc... I advised him to put down some shredded wood mulch (wood chips also work well) = making an 'island' look in the middle of a sea of grass - and plop down a bench. Worked like a charm. They added a few other nice 'props' to complete a quiet forest scene. He and his wife sat out on that bench and got lots of nice complements for the look. If you can't beat it...

Those are good ideas. Shade is not an issue because, as I said, there are shadier areas under the branches that grow grass fine. I took a spade and pushed it in under the tree, and a few yards out in the grass. The penetrability was indeed better in the latter, presumably because of oak roots in the former. So that's a clear problem. But not even many weeds grow there, and weeds are very tolerant of impenetrable soil.

To the extent that the allelopathic poisons break down readily, I'm not sure germination in soil samples will be a good test. May require live roots.

But I think as a result of this discussion I've concluded that oak leaves are not a threat. Many thanks.