I think you may be overthinking this :-)

First, mulches - even fresh, wood-based mulches - do not "rob" nutrients from the soil. There may be a little nitrogen tie-up at the soil surface but not enough to get in a lather about. It is only when wood-based products are incorporated into the soil that you need to have concerns about nutrient unavailability and even that is usually temporary.

I'm also confused about the issue of 'souring' (whatever that may be). Organic mulches, wood-based or not, do breakdown and decompose in time and doing so add nutrients to the soil. If by 'souring' you mean this process of decomposition and the natural fungal offshoots, it's all perfectly normal. Turning just speeds up the process - not turning or a static composting results in the same product. It just takes more time.

I'd recommend selecting whichever meets your budget and offers the best appearance - they'll all work about equally well as a mulch.

btw, bark mulch comes in various grades and is not all that lightweight unless finely ground. I've not had it be a problem in any wind, although it can slide on steep slopes with heavy rain or irrigation.

From what I've read, mulch souring refers to the build up of toxic gasses (and liquid) that occur when plant material decomposes without being turned. The turning releases the gases and brings oxygen back into the process. Supposedly sour mulch will kill your plants. They say it smells like amonia. The local mulch places have to turn piles of mulch occasionally by law to reduce the emissions. Some places even monitor the air.

That's my laymens explanation, sine I ain't no biologist or chemist.

Oh I guess I should mention that since I haven't mulched in 2 years, I've had some soil erosion, so the mukch will be sitting on some of the plant roots. I don't know if that matters in regards to the whole nitrogen robbing theory.

Oh and the cooked an composted mulches supposedly kill off insects, diseases, fungi. Another factor.

Any ammonia odor from decaying organic matter is Nitrogen escaping to the atmosphere, something I've not smelled in wood chip mulches. The only time any mulch would be a problem and kill plants would be if the mulch is put down too thickly. I have smelled an obnoxious odor coming from piles of wood chips, shredded bark, etc. that is piled up more than a couple of feet thick, but seldom anything less than that. I have also smelled an odor of the wood from smaller piles, for a short time, however that is pleasant and does no harm.
Processing of mulch materials to kill off insects, diseases, and fungi is counterproductive because even after you do that they will move in again, and if the beneficial types are killed off (as they will be) that means the pests and pathogens can grow with nothing there to aid in containing them.

They pile the mulch, sometimes for months, in piles over 10 feet tall.

Still not sure which to get....guess whichever is cheapest?

I'd get whichever would last the longest, which would be the ones that haven't been composted.

I have used shredded pallet mulch and it lasted a long time. It looked nice after it got some water and aging. I can get a heaping truck bed full of shredded pallets mulch for around $20. So that is what I usually get when I need to supplement my leaf mulch.

I primarily use shredded leaves for mulch.

Just about the last thing any gardener would want is a mulch that teally lasted a long time since that means the soil is not getting fed. Shredded leaves are a very good mulch material because they 1. are free, 2. quickly add organic matter to the soil, 3. aid in weed suppression, 4. aid in soil moisture retention, and 5. aid in keeping the soil cooler. The drawback to shredded leaves is they are digeted quickly, but they are also readily available each fall.
Wood chips can do all of that and they do last somewhat longer, depending on which tree they came from, but usually wood chips can be fairly expensive.
The best mulch is the one that will do what you want it to do at the least cost to you.

Just about the last thing any gardener would want is a mulch that really lasted a long time

Except for me...I don't want to have remulch, every bed, every year. So if I am going to buy mulch, then I want to buy something that will last.

Did some research. Found these two articles/studies helpful:

http://www.extension.iastate.edu/Publications/SUL12.pdf
http://ohioline.osu.edu/sc186/sc186_14e.html

Main Conclusion:

More composted yard waste in your mulch = more organic matter , less compaction, more NPK, more growth, more flowers, and less nitrogen robbing

If you are not using highly composted yard waste (heartwood chips), add nitrogen

Summary:
From Worst to best wood muches:
Ground Pallets - decays fastest and robs most nitrogen
Dyed Ground green wood - decays fastest and robs most nitrogen
Partially composted hardwood bark or young softwood tree - decays slower, but little nitrogen to aid decay
Partially composted hardwood (trees and branches) - decay faster, but contains more nitrogen
Partially composted yard waste (brush, stems, branches, leaves, grass) - decay faster, but contains lots of nitrogen
mature softwood tree bark (pine, cypress) - decays slowlest so less nitrogen robbing

Conclusions:

Unless you are using pure mature soft wood bark, which is impossible to find, use mulch with the highest amount of nitrogen rich (smaller plant parts) yard waste that has been composted the longest.

Make sure the mulch supplier sprays mulch with water and turns it occasionally to avoid souring.

If you want slow to moderate growth on bigger plants like trees and bushes, and better insect resistance (due to the stressed plants producing more defensive chemicals), use mix with more bark and woodchips.

I guess your conclusions depend upon your goals.

If you are using mulch to feed your soil, then your conclusions are correct.

I don't use mulch for that purpose... I feed my soil with compost and then I use mulch primarily for weed suppression... and then I'll take the other benefits of mulch, moisture and temperature, along with it.

So you put a layer of compost under the mulch? That seems like twice the work, not including generating the compost (maybe 4xs the work). Wouldn't it be easier to just add composted mulch ever year along with a little extra nitrogen?

Speaking of which, what type of nitrogen would one add? Just some osmocote to the base of each plant, or something spread or sprayed over the entire mulch? Can't be too hard.

Making compost is very easy...I just pile stuff up and Mother Nature does the work. Twice a year, I will dig finished compost out from under the pile.. it mainly goes on my garden. If I have enough left over I will spread some on the lawn areas or some in the flower beds.

I bought Timberline 'Hardwood Mulch' at Walmart in Mt Airy MD.

May 2 2010 bought 20 bags
May 4 2010 bought 17 bags
then I bought another 20 bags on may 22, 2010

But the mulch looks like brown and not dark like the other 37 bags.

I've sent email to the company at myoldcastle.com but have not got a response yet. It looks like brown mulch. I used brown last year and still had one bag left.

I can send a pic to show both beside each other. any one out there buy the same mulch around early may from Walmart in Mt Airy MD?

thanks
Jamie

I guess I'm too cheap to buy mulch. I have found that tree services are more then happy dropping off a load of chips for free anytime I want some. I realize that there could be some undesireable stuff in it like black walnut but never had any trouble using it.

What I like to do is to put the coarse chips through my Troy-Bilt Super Tomahawk which reduces it to much finer bits. This wood mulch is for the blueberries. They love the stuff. It breaks down well enough to feed them and keeps the soil acidic at the same time. If I wished, I could add some coarse chips on top for a longer lasting mulch but that's not my goal. I want to feed them and my fine mulch does the perfect job if I do it each year.