[landarc]

naughty materlvr...the green bin is only for green waste, not heavy clay soil...I also fail to see why your being a woman matters with drainage, if you have kids, you have landscape laborers

Anyway, if the growmulch you are using is the mix of screened aged forest and wood slash and garden clippings that I am familiar with, then you should add some sand, at the least, to create a substrate for the soil amendment (growmulch) to bind with. A good topsoil would be better, as sand is primarily a nutrition free planting environment. It is easier with a little loam to manage soil moisture as well. The fact that you used trenches is probably why drainage was not an issue.

So, yes, for use with any plants, mulch is not sufficient as a singular growing media. Typically, I would specify 6" of soil amendment to a depth of 12" to 18", so the ratio would seem to be about 25% to 30% amendment to 70% to 75% sand or sandy loam.