if you're talking about newly planted trees that you want to establish well, the mulched area (not compost, but wood chips) should extend to the drip line.

The feeder roots of trees extend well beyond the trip line, so go a foot or two beyond it. As long as it is coarse enough to avoid compaction and relatively free of weed seeds, compost is fine. I would not use fresh wood chips. Under the right circumstances wood chips can cause nitrogen depletion. All in all, bark mulch would probably be your best choice.

It is a myth that wood chips on the surface cause nitrogen depletion. Many gardeners, like me, use wood chips extensively for mulch, and in my sandy, nutrient deficient soil, you'd know very soon if the surface mulch was causing problems. In fact, as the chips degrade, they add nutrients. Wood presents a problem only if it is buried. BTW, in terms of degrading, bark and wood chips are pretty much the same thing.

Agree with Lacyvail here, in that while "nitrogen drag"-the term the big guys use for this phenomenon, is a real thing, in practical terms, and especially when the low-N material is being placed on top of the soil surface, this is virtually nonexistent. Some drag can occur in different systems, like where a large stump has been partially ground out but where a lot of wood remains. And even this is easily mitigated via a moderate application of fertilizer.

OP, you're in Z7, and that's likely the biggest worry here. Birch are denizens of the cool north. What birch species do you have? If by chance river birch, that is helpful for you in your location.

Finally, some compost with woodchips or bark is likely ok, just not a big deal. Remember, the goal isn't to make that tiny circle of soil around your newly planted tree extremely rich. The goal is for that tree's roots to extend far and wide, as they will have to do in order to provide what the tree is going to need to grow. For that to happen, no special treatments of the backfill area is going to help.

+oM

Guys, is size of the tree at all important? I imagine my shingle oak would be happier with no grass competition. That thing however has a 90 foot spread! If I had to I suppose I could use round up the grass but I suspect spraying that much on the bermuda/zoysia out near its eastern limits might kill some bermuda out further since it lives off the runners. If the shingle oak were a suckering tree I couldn't even use round up for fear ofnkilling the parent when I killed the suckers. can't just scalp the soil either w/o making the tree angry.

What is the suggested method of clearing grass if it is a large tree?
Also, Bridget, was there an arborist over because something isnwrong with your tree or were they just giving advice in general or what is the situation?

Suggest that you avoid spraying. If the tree is already in the ground and established, I would just give the area a buzz cut with the mower/trimmer and throw down 3-4 inches of mulch. The grass will be dead in a matter of a month or two (depending on conditions) and the grass root material will be dissolved in roughly six months. Grass or weeds may pop up in spots, but you can just spot-treat or yank them.

For new trees, I try to mulch a 5-7 foot radius, depending upon the eventual size of the tree (and if space allows). Smaller than 5' is not that useful for the tree IMO (outside of the first couple years) and also a tough turning radius for the riding mower. In the back yard, I will take them out to ~10 foot radius for the big shade trees as they mature. You have to judge what is practical based on how much space you have, the look of your property/neighborhood, etc. As you get bigger mulch circles, you can look for and plant benign flowers, shrubs, groundcover, etc. that are less competitive with the tree for resources than grass.

My yard is pure clay, so I mulch generously the first 2-3 years with leaf compost/humus. Thereafter, I rotate leaf compost with bark mulch. Leaf compost is very good for the soil - my perennials practically jump out of the ground within a couple days of top-dressing. But it is not the greatest at keeping weeds down. It breaks down more quickly than the typical ground-up pallet-mulch that is ubiquitous, which can be good or bad depending upon your perspective. Bark mulch is a better weed controller than leaf compost and is better for the soil than pallet-mulch, but it can take longer to break down. If you use it annually, you may find your mulch circle rising. Hence the rotation.

Do mulch, don't amend. Wood chips are best when plants are not so tiny they can be smothered. With all mulching you want to keep the mulch well back from plant crowns anyway.

Toronado--I'd say a tree with a 90 foot spread has outgrown any problems of grass competition.

crikey ...

as big as it needs to be.. to keep the idiot on the riding lawn mower.. or the ditz with the weedwhip... away from it ...

do NOT use compost ... MULCH ...

after that.. its usually a function of whether or not.. you want to put some other plants around the base ...

you dont mention.. or i missed... whether this is a new planting ... i have a feeling.. i recall some older post... ???

all the rest above.. is theory ... i mean really... it is said.. that an established tree.. is twice as big below ground.. as above ... in a pancake form ... to think you need to mulch a circle that big.. could get surreal ...

whole other world.. if its a recent.. large transplant ...

i would go much more than a 4 to 6 foot circle ... i would kill the grass with round up.. and lay 2 or 3 inches of mulch on top .... and be done with it

ken

ps: in my yard.. i am the idiot and the ditz .. some days.. even 4 feet isnt enough... if you sneeze at speed with a zero turn lawnmower ... lol ..

I am aware of some parks departments in NE WI who, facing decline of centuries-old oak trees, did in fact mulch huge areas. I am less well-aware of the outcome of these projects. Even the city I work in-I supervised this job-did roughly the same thing in a park where the old oaks started dropping off. But then the summer of '93 came along-heavy rain nearly every day all summer! That area had been dammed up by park road paving project which raised the elevation of the road surface, such that those trees never had a chance. So what was learned? Not much. That area is now a playground, and yes, new trees were planted.

But as a practical matter, unless there's something wrong, no, I wouldn't suggest someone "needs" to mulch around an old, established, and healthy tree. One more comment: We constantly here advocate mulching but not soil amending. I myself am in that camp. But.........if a sufficiently large area can be so treated, that changes the dynamics greatly. At that point, we would no longer be creating the drainage anomalies and other undesirable effects of amending backfill soil at planting. This is really a different thing and should be treated as such. True, there may not be much published data suggesting improved plant performance when large areas are amended with organic matter, but this practice does create a more forest-like environment and something about where trees originally came from strongly suggests-to me at least-that this could have merit.

Finally, agree with poster above that leaf compost is extremely good for plants, although my primary usage has been as an amendment in annual and perennial display beds. To say it makes a difference would be a huge understatement. And yes, I know, some think the proper name is leaf mold. I don't and I know that's just a quaint, outdated word for compost.

+oM

"...if a sufficiently large area can be so treated, that changes the
dynamics greatly. At that point, we would no longer be creating the
drainage anomalies(.)"

Not true, except in special cases (like on the side of a hill or something). A large "bathtub" is still a "bathtub".

A lot of advice! Thanks. The trees were planted about 10 years ago and look good to me. I have weeded around the crown about a foot but hadn't done it yet this spring. We have someone come out regularly to "feed" our trees and shrubs. They also did the original landscaping. They always give us suggestions and how to care for our yard and were the ones that suggested getting rid of the grass and composting. I didn't ask how much. I went out and weeded/got rid of grass about two feet radius. The amount suggested here would take up half my back yard and some of my neighbors. I am inclined not to use roundup though it doesn't seem so bad. I do it by hand. No problem with the mowing. Again thanks.

Brandon, we've been down this road before. But tell me something: Are all the wooded areas of the country, with their constantly dropping leaves, twigs, etc. turning themselves into sites unsuitable for continued tree growth? Bathtubs? I think this a good example of taking something for which you can formulate a rationale, and then carrying it far beyond the point of reality. Our urban landscapes are chock-full of impediments to drainage. At the same time, modern grading practices are hyper-draining our lots and building sites. That is, to me, such a pinched-off view of what is before us. I'm sure you could set up the perfect situation where, by adding OG, you could still have impeded drainage. But this amounts to picking all the lowest-hanging fruit, and then declaring it is representative of every apple on the tree.

We've done soil amendments of this type forever. It is, IMO, downright silly to make it to be some kind of villain like you have-an intellectual exercise, divorced from a far more forgiving reality.

+oM

+oM, I am not absolutely sure exactly what you meant at every point above, but my point is simple...poorly draining soil is poorly draining soil no matter how large the area is. I see no reasonable way to doubt this if one just thinks about it logically. A perched water table can be many acres or as small as the bottom of a flower pot. It's not the area that makes a difference.

And my new point-upon re-reading OP-is that this thread is simply not about drainage (although it does seem like every other thread is!). If the subject is soil amendments, my rock-solid conviction, based on decades of experience as well as a high degree of "book learning" is that it is not only acceptable, but desirable, to amend large areas pre-landscaping. And it is equally unhelpful to amend backfill soil of individual plants. And............as along as we're talking about it....vast areas need no special treatment of any kind, but typical soil-stripped suburbia is especially lacking in decent soil of any depth beyond what Mr. Developer needs to get a catch of grass growing. Those are the types of sites where whole-yard amendment may be especially useful. Where I live, 100+ yr. old house, the soil is deep and rich. Contrast that with modern development techniques, which BTW, I have no idea if that applies to OP's situation-he's just wondering about his birch tree and you and I and everyone else disabused him of the notion that making a little tiny circle of enriched soil does any good whatsoever, for a tree which, if it is to survive and thrive, needs to send out roots far, far beyond that circle. So in the end, we're arguing about something that this thread is not about!

+oM

+oM, I doubt anyone would argue, in general, about it possibly being beneficial to amend a large area before planting. But, it's not a one-solution-fits-all type of thing. There are many factors to consider, and drainage would of course be one very important one. In most cases, drainage is not improved by amending soil, whether in backfill or in large areas. Also, amending soil is not necessarily the best way to deal with the vast majority of situations out there.

Here in this case, I'm not sure it's even much of an option since the tree is an existing planting. One could do the crazy compost-fracking thing, but that's highly unlikely to help, and has many potential negatives.

As others have said, it seems like a proper mulch application is what is called for here.