Its an experiment with your soil for sure. Do you have nothing else to do with the stuff? Annuals are where all that fertilizer belongs, the live fast die soon thing. What IF I got my 90ft oak hooked on a ridiculous amount of xxxx when it was little only to find if I didn't provide it every year the tree would die.

If you think your soil is missing something you can either experiment on your own or send it off to get tested. I really prefer just to see what grows on its own. Don't want to end up babying non-hardy 40 foot + trees.

Here is a link that might be useful: Soil testing links

When people mow their yards & don't remove the cut grass, which can form modest piles, doesn't it do much the same thing over a tree's root zone?

That said, how much compost are you wanting to add, and what is your purpose in adding it? If this is traditional mixed compost that's very 'soil-like' and contains some soil, too, be mindful that adding substantial amounts of soil over a tree's root zone can be harmful.

Just what kind of 'compost' are you considering using?

Richard.

Mulch serves several puposes: keeps soil cooler and more moist, suppresses weeds, creates an area you don't have to mow or risk the the tree's bark with a string trimmer. Compost is a great soil conditioner, but not a very good mulch at all. It usually contains weed seeds, often is too fine so it forms a crust which sheds water, and can actually blow away under the right conditions. Bark or other coarse material makes a much better mulch and preserves the compost for use as a soil amendment. You could add a thin layer around the trees and then add mulch on top.

Is it bad to use compost that has some grass clippings and weeds in it to mulch around a tree? I read somewhere that the composted grass clippings could affect the soil ph and harm the tree

It's not "bad". You won't do much to the pH umless you do it a lot, but why? It won't be performing the purpose you want, as it won't be a very good mulch.

Dan

The best place in the world for your grass clippings are right back from where you removed them. If you mow high, on a regular basis, and use a mulching blade, you will be doing a great thing for your soil and the lawn. No more bagging those clippings!

People get into trouble with excess grass clippings when they mow infrequently and/or fertilize too much.

Anyhoo, composted anything doesn't make a good mulch, as has been said. The physical functionality isn't there. Compost IS, however, a great product to use as a top dressing for any kind of plant. It's a 'feed the soil' situation. Our urban trees don't typically have the benefit of forest duff. Compost can make up for that. Just don't consider it a substitute for a good mulch.

in my experience.. grass must be thoroughly composted to be used as a compost or a mulch ...

green grass is neither... as it leaches nitro in the rotting process and can clump into an anaerobic mess that will stink to high heaven ....

if properly broken down .. in a compost pile.. it should have little or no effect on soil ... unless you were to put 50 tons around one plant ...

changing pH in a significant manner takes LOTS of anything ... as its an exponential function .... if those are the right words

ken

I'm going to disagree :-) There is nothing inherently 'wrong' with using compost as a mulch - it functions just as well as any other mulch product ("mulch" is anything applied to the top surface of the soil, not a specific product per se) in that it protects the soil surface, offers weed suppression and moisture retention and provides a degree of soil insulation. It is the mulch of choice for me and I use it to mulch everything in my garden. Because it tends to be more finely textured than some other mulch products and relatively nutrient rich, it can lead to encouraging the germination of blown in weed seeds, but these can appear readily with many other mulch products as well and are easily addressed. And I prefer the aesthetics of a compost mulch but that is not my primary reason for using it.

Mulching an area surrounding the base of trees is always a good plan, regardless of material chosen. It accomplishes all of the mulch requirements (see above) and prevents competition from turf grasses and potential damage from lawn mowers and/or string trimmers. You just want to avoid piling on the mulch too deeply and keep it away from the trunk. Unless you are using something very unusual for a mulch, it will not impact soil pH nor harm the growth of the plants it surrounds. Some folks DO use grass clippings - straight/not composted - as a mulch and while they would not be my first choice, they offer many of the same attributes as any other type of mulch.

IME, as both a horticulturist and a teacher, I have discovered there is a great deal of confusion about mulches and mulching in general. Comments made in this thread just confirms that.

How big is the tree? Even if the mulch could affect the soil pH, if this is a small ring around a large tree, only a small %age of the root zone would be affected.
I prefer wood chips or pine bark as mulch around an established tree. I agree with gardengal that compost can serve all the normal functions of mulch, but the woodchips and pine bark last longer, and in my experience, weed seeds are much more likely to germinate and grow well in the compost.

Alex

all green grass.. can cause an impervious mat.. which will retain heat.. and deny water going thru it .... which is NOT a mulch.. nor is it compost ... [and it will stink to high heaven while it is rotting]

otherwise.. what gal said ....

ken

GG is technically correct, and IMHO in this context you want to discourage grass around the trunk. Compost won't do as good a job as other things, and you have to keep piling it up which is bad for the trunk.

Dan

If they are composted weeds and grass clippings the only drawback to using that as mulch is that it won't last long. It will break down quickly and feed the soil. I often bulk mine up a bit by adding raw or semi-composted pine needles.

tj

Thanks for the responses. Let me clarify a few things so I might get a more conclusive answer.

1. I don't really know the different types of compost (if there's such a thing), but my compost pile is made up of mostly fallen leaves, some grass clippings, some weeds I've pulled, and a small amount of "other" (eg. twigs, rotten fruits, xmas tree pine needles, etc.)

2. The compost mix would be completely "cooked" (composted), so definitely not putting freshly cut grass clippings or pulled weeds before it's turned for some time.

3. I guess I could use the bag of mulch you buy at the big boxes, but I figured this is free since I started saving it instead of putting it in the landfill.

4. I would put it in a garden, but I don't have one. Just have lawn w/ trees, so if I can't or shouldn't use it, then off to the landfill it will go.

So from the responses, it seems most, w/ the exception of GG, think compost does not make a good mulch. Although I like GG's response best, very thorough and convincing. See why us newbies are so confused :-).

Thanks everyone.

You put a mulch ring around your trees to avoid mechanical damage to the trunk. It is sorta aesthetically pleasing as well. And it does do a bit to help with tree health in turf. That is the reason why you do that.

Next, you want to think about how much work it will be to maintain that mulch ring around the trunks in turf. Do you put something around the trunks that requires a lot of maintenance to keep looking good and avoids mechanincal damage at the same time, or do you put something around the trunks that fosters turf growth and requires time and energy to keep free of turf and associated weeds?

Dan

If the compost is already ready and available and you have no other place to use it, then I'm not sure there is much issue for debate :-) Most any source will list the benefits of mulching trees -- it's just a matter of determining what type of mulch to use. And that choice is pretty much whatever you want to use......or have on hand. In many respects, any mulch will achieve similar results - weed suppression, soil protection, insulation and moisture retention.

Yes, compost can make an attractive and rather fertile seed bed. And it does not last as long as other, more woody based mulches might. But if we are only talking about mulching around a few trees, neither of these two issues presents overwhelming difficulties. Pull whatever weeds may pop up during the season (easy to do with a fluffy, loose mulch) and replace as necessary. IMO, the benefits that compost offers in the form of a mulch, including a higher and more readily available nutrient component than most other mulches, easily offsets any potential drawbacks. And you already have it on hand :-)

So from the responses, it seems most, w/ the exception of GG, think compost does not make a good mulch.

As you can see, it all depends upon what your definition of 'is' is. ;o)

Dan

Great, I now have a better understanding of the pros & cons of using compost as mulch. That leaves me to this question. If you had to pick one choice of mulch to use around a tree, what would that be?

I'm still wondering why you have the leaves and grass clippings accumulating in the compost pile in first place. If you don't have a garden or some applications to use the compost, why not mulch it back into the yard for a much healthier yard (including your trees)? I never bag my grass and only very rarely rake up any leaves. Even in the fall, a mulching mower will make leaves disappear and add to your soil.

I mulch around my trees with pine needles or shredded hardwood mulch. The things I would consider when mulching around trees are:

1. Mulch wide, not deep. You don't want to smother the tree's roots
2. Keep the mulch away from the trunk. Especially avoid mulch volcano situations.
3. Use something organic that will add to your soil as it breaks down.
4. Use something that will last a while (but not forever). Frequently having to remulch is not good for you or your tree.
5. Use something that matches your yard or something you like the looks of.
6. Consider maintenance. You probably want to avoid a mulch that needs to be frequently cleaned out or reapplied to look good.

Here is a link that might be useful: Benefits of Mulch

If you had to pick one choice of mulch to use around a tree, what would that be?

Shredded wood chips from my pruning activities.

Dan

brandon7 - I use to leave grass clippings on the lawn, but mowing low & twice a week (Bermuda grass), the clippings don't decomposed fast enough & yard starts to look messier and messier. On top of that, neighbors weeping willow keeps dropping leaves & twigs to add to the mess. I use a reel mower, so mulching mower out of the question. Anyways, thanks for link & tips, will put it to good use.

>If you had to pick one choice of mulch to use around a tree, what would that
>be?

For a newly planted small tree, I use compost for the first couple years, for the reason gardengal gave:

>IMO, the benefits that compost offers in the form of a mulch, including a
>higher and more readily available nutrient component than most other
>mulches, easily offsets any potential drawbacks.

For a large tree, a mulch ring will affect such a small %age of the root zone, that advantage of compost is negligible in my estimation, and wood chips are more convenient.

In short, for a small newly planted tree, compost. For a larger established tree, use wood chips or bark. For an established tree that doesn't get big, like a dogwood or small japanese maple, where it's easy to mulch a large portion of the root zone I'd be inclined to stick with compost. All my opinion of course.

How big and old are your trees?

Alex

Composted material is more of a top dressing than a mulch. A good mulch has a coarser texture than compost, making it more effective as a mulch than well broken down, finely textured material.

My preference is for cedar play chips.

alexander3, trees are between 12-16ft, 2-3in caliper, newly planted about 9 months ago. So I guess that would make then somewhat small & young. If I were to use the compost now, at what point would the trees be "old enough" to switch to a different mulch?

I've never planted a tree that size, but I'd say once you feel they are established and growing well. There's a saying about planting trees:
The first year they sleep
The second year they creep
The third year they leap!

Once they "leap", I'd guess the benefits of compost over wood chips, at least in a typical sized mulch ring, are not much.

Alex

Where I work (a large company campus) they collect the coffee grounds, grass clippings and leaves and make compost. They spread some of this compost under the many trees on the site. It seems to work beautifully.

Trees form mycorrhizal relationships. Feeding the soil with compost seems like a very good way to encourage fungi to live underneath the tree.