The absolute BEST mulch to use is cocoa shell mulch. Approximately 2 - 3 inches will keep most weeds down, and there's no ill effect upon the soil. Lasts for a couple of years before it needs refreshing. The serious down side is that this stuff can be VERY poisonous to dogs, who are attracted by it's chocolatey fragrance. So I wouldn't use it unless you have a jump proof fence around your garden. Cocoa shell is somewhat available in the MD/PA areas, as a by product of Hershey's chocolate making process in PA. Not sure about other areas.

I don't formally mulch my garden. In the backyard, it's a shady woodland garden dominated by white pines, a huge green ash and a red oak. Leaves and needles that fall in the beds are left where they are. Whatever falls on the lawn is chopped with the lawn mower and spread on the beds. As others have mentioned, the oak leaves are late to fall - in fact about 1/3 don't fall until new growth starts in the spring! DH uses a leaf blower on the vacuum setting to vacuum them up (which also shreds them) in the spring and they get added to the beds in the spring. One problem with leaves as mulch - in my garden at least - is there is a lot of seed keys mixed in so a regular patrol is required, particularly in early summer, to yank tree seedlings as soon as they appear! In the front garden, there is not a ready source of leaves. All the trees there are young and still too small to produce much of a leaf fall. I use feverfew in the front beds as a filler plant. In late spring/early summer I cut back all the feverfew by at least half and leave the cuttings on the ground as a green mulch. Also, I don't clean up the garden in the fall - other than anything diseased or disease prone. In the spring I just remove any tough stalks that are still standing and pull any dead stuff away from crowns if it looks like something is being smothered. Other than that, all the previous year's dead foliage is left to compost in place. By mid-May new growth has covered everything so there is no visible mess. The garden (and the soil) seems happy with that approach and it sure is a heck of a lot less work! (And, no, I don't have a problem with pests of diseases. I suspect that the feverfew, with its scented foliage, may work a bit as a deterrant.)

I was reading this old thread. Some are not around here anymore, but I see jolj is...greetings gardening friend. I'm still gardening here in Indiana. I have amended most of the three gardens. with sand, local peat moss and add partially rotted manure, very finely chopped leaves, and chop up residue in situ. The crops grow very well. Yes, I have a tiller. It does some weeding, it prepares a row for seeding, it tills into the soil amendments and organic additions, and I tend to ridge up many of the rows for spring planting. It's not that I want ridged rows after planting, but that the tiller leaves them just right after the row is planted.

I do mulch around the irises, and it does help with weed suppression in early spring. The irises are so interplanted with other plants there is little room for weeds after things are up and going in late spring. I hand pull the johnny-jump-ups and the like that self seed into the middle of a clump, but otherwise there's just no where for a weed to grow in the beds by early summer. In spring I wait until the weeds sprout then mulch so the seedlings suffocate and die, otherwise the seeds just sit until they hit the surface again and then sprout. In my small garden this is relatively easy though. It won't be feasible for everyone. And the downside is I am constantly battling leafspot because of no air circulation between the plants. Mike