I have a lot of raised beds gardens that need topping up this year. I’m wondering if it makes sense, can I dig a huge hole of soil from behind my shed, and then fill this hole back in with (to be) compost? I know the compost fill will keep shrinking, but does that make sense otherwise?
It might depend on your soil type. I've dug trenches in silt before and they end up filling with water for at least a week after a good rain - being water logged might be troublesome for composting, especially with clay soil.
I tried in-ground composting with dried grass and aged manure in sandy soil last year, but results are still pending. From what I saw in the fall, after such a dry year, the straw seems to be breaking down alright.
Aside from that potential issue I can't see why not. My yard had many dug areas from the previous owner and with grass clippings and leaves alone they're filling in nicely after 3 years.
I guess the only thing to consider is how good is the soil behind your shed. If it's just been grass there the whole time, it might not be that good - especially if the grass is collected in a bag instead of left on the soil. If it's just bare soil where nothing has grown in awhile, it might be worse since it'd be lifeless. It might be more efficient to just buy a couple bags of potting soil or something, or to do a half/half with potting and your other soil.
Anyways, many factors to consider, but that's all I've got time for.
Best of luck and happy holidays ^^
"Our ability to change the face of the earth increases at a faster rate than our ability to foresee the consequences of that change"
- L.Charles Birch