Here is one of the easiest and least costly ways to build healthy soil: collect excess leaves in October, put them in a pile, dampen them a little, and place a tarp over the pile to keep the leaves from blowing into the neighbour’s yard. That’s all you have to do. Turn the pile a couple of times if you want the exercise. Let nature do the rest.
Be sure to put the pile in a corner of the yard where it is out of the way. It will take a year for the leaves to break down enough to be ready for digging into the garden soil. The smaller the leaves are to start with, the faster the bacteria and fungi will chew them up. Large poplar leaves, for example, will take longer than small elm leaves. To speed things up a little, I sprayed my pile this year with an organic microbial inoculant generically called Effective Micro-Organisms (EM). This liquid is similar to compost tea, in that it contains a multitude of beneficial bacteria that will transform the leaves into plant nutrients.
The end product is a fluffy brown material that is one of the best conditioners for heavy clay soils. When lightly worked into the soil, it reduces compaction, improves air flow, increases water-holding capacity, and adds nutrients (especially potassium). It has a neutral pH (around 7), which is in the ideal range for most plants (6.2 – 7.0).
When it is ready, spread a couple of inches of it over your soil and turn it in with a garden fork to a depth of 3 or 4 inches. It doesn’t matter if the leaf mould is not completely broken down when you apply it - the soil microbes will soon finish the job.