I might agree with you guys if we're talking about a real fine, dense, mulch. I still think that 6" of the mulch that steve and I got or even a deeper layer of fresh tree trimmings is OK. That 6"-8" layer of chunky mulch will quickly settle and compact down to 4" within a few months. And if we're talking pine needles then 12" deep is no problem; that 12" will settle down to 4". Of course if you're watering from above you're gonna use a hell of a lot of water before that water hits the ground.....something to think about. If you're using drip, where your emitters are burried down at the lower layers of the mulch, you're fine.