I'm experimenting with different soil mixes for my terraces. I'm having to build from the ground up (so to speak) since I have bright orange (red) clay and nothing else.
I bought a scoop of so-called landscape mix from my local co-op. It is equal parts topsoil, mushroom compost and sand, and it was screened. I spread it 3" deep over a 3" layer of mushroom compost which is over red clay scraped clear of grass and double-dug very choppily with a shovel. I did NOT mix it because I wanted to SEE what happens with rain. We got about 20 minutes of rain. And the mix is mud. It's sloppy. And the landscape mix is holding a LOT of water. The compost is draining just fine and staying DAMP but not SOAKED.
I don't like it. Good soil should drain, shouldn't it? I'm wondering if screening it removed all the big chunks and made it too uniform in size. I'm wondering if this is the same problem people find when they till too much and remove the structure of the soil.
The soil mixes I like best are 2 (or 3) parts mushroom compost and 1 part topsoil, mixed roughly with a shovel. The compost is chunky and has many different sizes in it. This is a good thing because air can get down into the soil. Right? Air can't move through the landscape mix at all when there is water. it's mud.
Or maybe I'm wrong on this one. I'm still learning. And I've been choosing plants that tolerate low water once established. So maybe I'm not seeing the big picture here.