I guess it's possible, but it could be a lot of other factors like how much water etc.. I use wood mulch, but a lot of compost mixed. I use a lot of stuff. You don't need grass to make compost or leaves, use free Starbucks grounds, bagged wooden mulch and table scraps. It good to add leaves if you have leaves but it is not required to add leaves or grass, you only need browns and greens together, look up this online. What is a brown and what is green. It is too long to post it right now.

Mulch doesn't really do anything to soil chemicals; it really just sits on top of the dirt (as a protective and visual barrier) and doesn't interact chemically with it. Where they touch damply, yes, there is rotting going on, but verrrrrrry slow rotting. You can functionally and chemically and fungally and conceptually keep separate what's on the soil from what's in the soil.

No language was harmed in the making-up of these words.

Thanks! I feel better now. AND I'm going to be recycling our coffee grounds. :0)

Here's an article about Mulch myths.

Here is a link that might be useful: wood chips as mulch

Just a note, it takes a lot of coffee grounds, just adding the few bits used it at home will not hasten up the process. You will want to get them from a coffee shop and I use as much as I can. Half of the bin should be coffee grounds if you can get that many. They are free anyway, the other half can be browns like bagged wood, leaves, dried up plant trimmings.

Many attribute far more benefit to coffee grounds then is really warranted. Coffee grounds are beneficial to the Soil Food Web, just as any other form of organic matter is. Putting coffee grounds into compost or on the garden is much better then sending them to a landfill.
But coffee grounds are not a magic elixir.
hoovb provided a good link above about wood chips as mulch since most of the bad about them is myth, not reality. Ma Nature has been putting wood back into the soil for eons, far longer than we have been around.
To determine why plants look sad starts with the soil and a good reliable soil test for soil pH and major nutrient levels. Soils in Southern California tend to be alkaline which can limit a plants ability to uptake needed nutrients. There may also be a nutrient imbalance that can cause a plant to not be able to properly use the nutrients that are available.

Evelyn, tell us where you read that if you can, maybe we can help dispel some myths. It's amazing what shows up in blogs, magazine articles, etc.

Re wood mulch being worst thing ever..."Wood mulches can also slow the growth of established plants and yes, just plain starve new ones to death by âÂÂtying upâ the available food in your soil, a process known as âÂÂNitrogen immobilizationâ :
http://www.gardensalive.com/article.asp?ai=552

Here is a link that might be useful: Re Using Wood Mulch

Re not using dyed mulch...

Here is a link that might be useful: Beware of Dyed Mulch

Another thing...dark colors (like black) would actually heat the soil more than no mulch at all probably.

Evelyn you've gotten great, intelligent advice here so please disregard the guy from the link you provided. The concept of wood mulch robbing plants of needed nitrogen makes NO SENSE , what do you think happens to mulch as it decomposes??? It enriches that very soil that was supposedly robbed of nutrients. It is a perfect cycle. More damage can be done with incorrect cultural practices than with cheap mulch . I still remember one if my gardening mentors saying that no mulch is worse than cheap mulch so go to lowes, go to WM and rest assured you're being a good plant mother.

But there is such a thing as applying such a thick layer that it becomes an impenetrable barrier to the detriment of your plants. The situation corrects itself as mulch decomposes but it might be too late for young and new plants, so don't go crazy with mulch either

Well, I'm so glad I posted on here instead of following the "wisdom" of the Internet. Here in Southern Ca, it gets so hot and dry, that I thought the least I could do would be to add mulch to try to conserve as much moisture as possible from the hose and sprinklers, especially since we're supposed to be conserving water with the drought going on. So I was dismayed to think I could be doing it wrong. Thanks to all of you.

Surprising information from Mike McGrath, former Editor of Organic Gardening magazine, who (as I recall) once touted using wood chips as mulches.
Most everything I have seen about high carbon materials, such as wood chips, "stealing" nitrogen from soils has been where they were used as a soil amendment not a mulch. Put any high carbon material in to the soil and the soil bacteria (if there are any) will get to work and temporarily use all of the available Nitrogen to digest that high carbon material. Once that job is done the Nitrogen is back for plant use, not gone as suggested by some.

And what was that whole thing about shotgun fungus spores being shot at your car and gluing themselves permanently? I've never heard of such a thing. Certainly the last thing that should be at the top of such a discussion.

I personally use wood chips between beds to form a walkway. It breaks down, or sinks down, or both. The weeds don't seem to mind it at all. As with most mulch, whatever we put it on top of dies (usually). But seeds that land on top of it do fine, provided they have enough moisture until their roots get into the soil below.

Of the things I've read, what's most consistent with observation is:
a) When applied as a mulch, any nitrogen depletion is highly localized. I can't test that, but I have witnessed that a variety of plants are growing there, and aren't sickly or slow growing, as you'd expect with insufficient nitrogen.

b) Whatever nitrogen the decomposition ties up is given back later and enriches the soil. No, I can't test that either, but my woodchip mulched soil is supporting plenty of grass and volunteer tomatoes now, and volunteer lettuce and lamb's quarter too, in the spring. They all appear quite green and healthy.

If you have doubts, I'd try it out on a small scale. I bet you'll find it works out for you too.