Can I use shredded conifer branches and l leaves?

I imagine your shredded conifer would have the same effect as the bits of trees and needles left behind after a forest clearfell operation (albeit on a smaller scale!). If they do, then any water filtering through it will tend to become more acid. The effect on your garden probably depends on what you are mulching - some plants would actually be grateful for the drop in pH and many others wouldn't mind, but many calcareous-loving plants wouldn't thank you in the long run.

A' best,

Mark

Rhodos, camelias etc, would like a conifer mulch. Any thing that likes acidic conditions as Peatysmoky says. A little wouldn't do any harm, just not a really thick layer across the enitre garden!

It would need to be left alone for atleast 1 or 2 years in order for it too lose some of its acidity, and then the spot where it was stored would be acidic, If it was in bags then the weather wouldnt get to it to leach out acidity!