So it seems that I’m going to have to disagree with even a respected garden writer like Amy Stewart. I read recently that she recommends 3-6″ of compost in the garden. While 3-6″ of compost top dressing the soil is better than 3-6″ of mulch, I still maintain that all you are doing with that much organic matter is inviting disease and rot into the garden.
You can read the piece where this recommendation was made here–it was a suggestion list for beginning gardeners. And believe it or not, not putting down this 3-6″ layer of mulch or compost is listed as one of the 9 biggest mistakes–it’s listed as #1.
Now while I would surely agree that failing to mulch or compost might be right up there–deep layers of either are no better and are surely worse! They invite disease, rot, fungal infections, critters of all sorts and worst of all, if gentle rains fall, they cannot even penetrate these deep layers.
Granted, gardeners should be using drip irrigation under mulch. But in areas that receive summer rains, the less one has to rely on the drip irrigation the better.
I’m not sure where this “the deeper the better” idea comes from. It may go all the way back to the 60s and the pioneers of organic gardening, Scott and Helen Nearing who gardened in Vermont and Maine. In their case, all this deep mulching might have served a purpose–they were gardening in some cold climates.
But they were also essentially doing what I call composting in place. And they were doing it prior to our wacky weather cycles of drought and deluge (although one might argue that weather is always unpredictable).
Still, to be sure, if you are gardening in a place that receives some rainfall, skip the mounds of mulch or compost and use more reasonable levels lest you be accused of creating “mulch volcanoes” in the garden.