When we lived in the suburbs, we only needed a couple bags of potting soil a year to get our seedlings going that we would use for transplants.
With our bigger property we have not only a need for more plants, but the resources to pull on to make our own potting soil. There isn't any peat lying around or bogs to dig up, but we do have plenty of old fallen trees that can be put to good use.
To get the fine humus that we want for a quality potting soil we are sifting the rotten wood and combining it with a sandy silt from an area near the old creek bed.
We are using white oak, madrone and doug-fir deadfall for the most part. Before mixing it all together you get some nice color contrasts from the different starting materials.
Our old compost sifter set-up, does the trick. Basically it is just a series of wooden boxes about 2' x 3' put together of scrap 2x6's with hardware cloth for the bottom of the boxes. We have several of these to help sort the rough (larger) material from the fine. The one in the pic below is 1/2 inch mesh, I believe.
Here is a 5 gallon bucket of the sand-silt from the old creek bed. A little goes a long way. The sandy material is really just to make sure the texture of the potting soil stays loose and doesn't mat together.
These are a couple flats that have been filled with the mixture of the screened humus and sandy-silt (~10:1 ratio). Once the potting soil is in the flats, just enough water was added to get the mixture moist and they were ready for planting.
My sons were kind enough to help in getting some cold hardy seeds sown in the flats, so now that they are hanging out in a bright area (but not much direct sun at this point), until we start seeing some sprouts.