Billed wrote:... I have always wondered which is better; a layer of leaves on the garden for the winter or turn them into the soil in the fall. I'm sure they compost better as a layer on top since more air gets to them. ...
I can share this opinion from my own observation and experience ... if you put a layer of leaves on top of the garden in the Fall and they are gone by Spring, it is because the wind has blown them away
because they have decomposed and "become one" with the soil.
Leaves alone are too "Brown" (carbon-rich) to effectively decompose within a few months. Plus, the wind and sun continually drys the top of the leaves [what few are not blown away], and that stops the decompostion as well.
Here's an example of what I am talking about... I had a 4'x4' (6" high) Raised Bed that I filled with leaves in the Fall (probably about a 4-5" layer of leaves in the bed). I covered the bed with floating row cover (Agribon) so the wind could not remove the leaves from the bed. The floating row cover lets water and air pass through; also, it will trap some heat, which would assist with "composting".
Guess what I had when I uncovered the bed in the Spring? ... a raised bed still full of very recognizable leaves.
Now sure, I am not saying that "zero" decomposition took place; I'm sure some worms "worked" the bottom of the leaf layer somewhat, and overall the leaves probably degraded a bit. But, don't expect "compost" from leaves that are "sheet mulched" or "sheet composted" on top of the garden.
I have heard people say... "I covered my garden with leaves in the Fall, and they were all gone by Spring".
I know where those leaves went! ... gone with the wind.