You are going to get a lot of different answers on this Dean. Everyone seems to have a combination that works for them. I like a mulch that is made up of many different sizes of media, as well as several different sources for that media, whether it's wood chips, bark, construction scraps, and yard waste. I have had great luck with mulch in a bag from the local big box store also but that gets expensive. You want 3-4 inches of a mulch layer. Remember the 2 most important things the mulch does is insulate the moisture in the ground and decomposes, feeding the tree. Keeping weeds down is another great benefit to me.

It looks like you are zone 4? I have been using wood chip mulch around my fruit trees here in north-central MN. I have the chips about 3 or 4" deep under the drip line of the trees, but pulled away from the trunks.

I'm starting to think that this has not been a good idea. The chips are a big temperature moderator and I don't think that it has been good at all. The weed and moisture control, has been nice, but the plus doesn't match the minus.

In the spring, the chips keep the soil much colder than un-mulched soil. This means that the growth season starts much later. This has really slowed the growth of my trees.

In the fall, the chips keep the soil warmer and this retards the hardening off process. This past winter, I lost over 1/2 of my fruit trees and had damage on my sour cherry bushes. I believe that they were not hardened off enough, and the chips were definitely a factor in this.

Last winter, we had - 30F temps in mid December. The chips had contributed to preventing the frost from going as deep as it should have by that time, and the plants weren't harden enough to survive.

I'm going to minimize my mulching in the future. Cold zones have as much, or more to loose by mulching, than they can gain by doing it.

Northernman, your analysis is logical but purely anecdotal and you've just gone through a test winter where many people lost trees in borderline zones, with or without mulch.

If mulch is a problem in early spring for keeping soil cool I suggest applying it after weather warms and trees are growing, mulches moderating affect on soil is generally beneficial- warmer at night and cooler during day, but the net is average cooler temps.

I doubt the mulch hinders hardening off as soil temperature is not a key trigger, as far as I know, (show me the data) but if I was worried about that I'd merely rake it away from the trunks a few feet in the fall. This is often recommended to reduce the risk of vole damage anyway.

As far as which mulch to use, there are advantages and disadvantages to various ones. Wood chips are free for the asking from arborists and coarse enough not to mat up and cut off rain and air into the soil which shredded wood mulch can do, but the shredded wood blocks weeds better and can occasionally be stirred with a fork to prevent this..

Leaves offer a better nitrogen to carbohydrate ratio if you want the mulch to boost vigor of trees, pine needles aren't as nourishing but attractive and affective as well.

Pine bark nuggets are available by the bag but get knocked around a bit by mowers and flooding rain. They hold up well.

Young trees respond well to mulch hay but it really needs to be pulled away from the trees in fall to discourage voles or you better set out poison bait stations. Weeds seeds are a problem in some situations, but usually not if area is mowed sod outside the mulch. For older trees it may be over stimulating. Same goes for stable waste (shredded wood mixed with horse urine and feces) which is best not used until mellowed for a few months.

I mulch with free horse manure that's mixed with bedding from the horse stable down the road. It decays and the worms love it. My trees do well with it. they have 60 sixty horses and a huge pile out back of the barn. I get the old stuff. They use the front end loader to put it on my trailer. I use it around my raspberries too. The raspberries really like it! It's tilled in my garden and I have a layer four inches thick on top. My tomatoes and peppers are dark green.