We collect our leaves in the fall and shred them, bag them and save them for just such an occasion. I put a 2" top dressing in the fall, by spring I am usually amazed by how much has vanished. In spring I clean up, fertilize and add 2" of shredded leaves. It really improves my soil, and slows down the weeds. We normally remove a lot of nutrients from the garden when we cut flowers, trim back growth, harvest or "cleanup" the garden. I will add much back with the return of shredded leaves, nutrients but not weight.