I generally use about 3-4 inches around trees, to the drip line and keep the mulch off of the trunk and root flare. 1-2 feet deep mulch?? wow I can't even picture this, but mulch volcano comes to mind.

To kill the grass you could pull back the mulch you have applied and lay down newspaper about 6 sheets thick, wet, and reapply mulch. Cardboard also works like the paper to block sunlight from the grass, but it can be harder for water to permeate it. If you are not opposed to glycophosphate, you might brush or spray the grass with this, allow it to die and then a week later put the mulch back. But with glycophosphate, you do not want any of it blowing onto nearby foliage or it will kill whatever it hits.

Studies have shown that raising the soil level around trees as little as 2" can eventually kill them. Mulch, because it is looser, can be applied a bit deeper - 2-4" for well drained soils but with heavy, clay soils no more than 2" deep. Unfortunately, you often won’t know if mulch is killing plants until it’s too late - sometimes the symptoms don’t show up for three to five years. You’ll probably first notice an overall decline of plant vigor and rate of growth, according to the Virginia Nursery & Landscaping Association. Symptoms can include:

Off-color leaves (pale or marbled)
Abnormally small leaves
Poor twig growth
Die-back of older branches
Rotting, peeling trunk bark under the mulch

And keep it well away from trunks or woody stems - 3 inches for young trees, 8 inches away from the trunks of older, well-established trees. Mulch should be applied widely, never deeply.

I'll add that the roots of the trees, slowly being smothered, will begin to grow into the mulch in order to locate oxygen. Roots require oxygen in order for cell division to occur. Those roots will be highly susceptible to dessication, heat and cold, lack of dissolved minerals found in the soil, loss of microbial interrelationships, etc.

I can't even figure out how many inches of rainfall (or irrigation) would have to fall before a single drop ever entered the soil system. It would take a flood of rain. That's the other reason why the roots will try to grow into the mulch.

Your bermuda, as a rhizomatous and stoloniferous grass, will soon emerge from the depths of all of that mulch, anyway.

Let me add that horticulture is not a stagnant science. Granted, as with all things, we can adapt some tried and true methods from the past and apply them successfully today. But we have thankfully learned a great deal about what is going on in the soil, and how complex and even fragile a working soil/root system can be. So we know with certainty that it is folly to apply 12 to 24 inches of mulch around the root system of any plant....no matter who said it was a good idea. ;-)

len

You are already noticing heat from your thick mulch......most likely damage has already been done to the tree roots. And it doesn't really make any difference if you are watering or relying on natural rainfall to irrigate the trees. That thick a layer of mulch will impede water penetration to the root zone regardless of method. And it can also retain excessive moisture in the soil, especially in your clay soil. This can lead to root rots. And then there is the whole oxygen issue.

You are very likely doing your trees irreparable damage with a mulch layer that thick. Your wood chips will take time to decompose......by the time they "shrink" to 4-6 inches (still too deep) the trees may be past the point of no return.

You don't have to believe me - do the research yourself. Virtually any site that discusses mulching trees and particularly the ISA website will say exactly the same thing -- do NOT raise the soil level around trees and do NOT mulch too deeply. The damage may not be apparent immediately but that doesn't mean it hasn't occurred.

Post this same thread on the Trees Forum and see what kind of a response you get.

In the winter, we pull it away from the trunk because of the small woodland creatures that find grass clipping mulch an inviting, snuggly winter home.

I am raising my primary garden veggie bed and attempting to re-start a 12 x 13 ft vegetable garden and am considering dumping several --6 to 8 inches of wood mulch (or more!) on it in the next few weeks with the idea that a lot will break down over the winter and be ready for some top-dressed compost around new veggies in the spring. I have HEAVY clay soil here and have fought this yard for 4 summers with very little luck. My veggies are average at best over the last few years; I've brought in YARDS of sand; composted horse manure; real topsoil; mushroom compost and surround the veggies with my vermicast each spring. Today, I just finished putting a limestone rock border around the area and it could likely handle approximately 14-18 inches of mulch. My clay soil (soil is probably a misnomer and I hate to even call it that) EATS all amendments I add and I am at my wits end.

With 6 or 7 months of time for an obviously heavy amount of free mulch from the city, I can likely get at least a foot on there. How much do you think it will break down in 6 months? Hopefully I won't get walnut mulch again which happened at a different house. At this point in the year I'll get some greens left which will get a bit of thermophilic composting going on so I'm expecting a bit of heat, but I think I'm ok with a foot of wood mulch. I'm going to remove the asparagus I have planted there prior and I'll be able to start 'fresh' with a new spot in the spring. I can (and may have to) remove a few inches in the spring if need be which I'm willing to do. I SO want to drop two feet on there and then 'skim' it in the spring.

This clay is a beast and I'm trying to prepare for next year. I am a seasoned gardener and I'm getting schooled by this awful soil and I can't afford thousands of dollars in compost over the next several years. I dump hundreds of dollars each year into this spot and am underwhelming my wife's expectations. The raised piece is my last hope.

Thoughts?

My take on the discussing; was that a large compost pile of wood mulch would take 12+ months to breakdown. (a 6 - 8 inch layer longer) A lot of that has to do with how finely chopped it was, my city uses a very beefy/thick chop... anyways, the finer the shred the quicker the composting, but you'll still need a source of nitrogen (grass, manure, etc...).

It was also discussed: using the wood chips as the bottom layer in a lasagna bed... most felt it would be detrimental rather than beneficial (robbing nitrogen) and felt it's best use in that scenario was on top, to hold moisture in (as mulch is supposed too).