We have been using a lawn sweeper on our large lawn for years and had accumulated a rather large pile of grass clippings and pine needles. The pile was added to significantly each spring and again each fall just before the snow fell in the fall. Once in a while, over the years, I had stirred it up with a rototiller to entrain some air and had even bought 5 pounds of redworms and waited for them to do their work. They did to an extent. We would use the composted material from the bottom as part of our potting soil mix each spring or as we needed for the garden. The pile grew faster than our ability to use it since it took several years for the clippings to compost completely.
I knew from my experience as a young boy on the farm how important it is to protect both grain and hay (especially alfalfa) from moisture both at harvest and storage. Excess moisture can cause “heating” and will spoil and in extreme cases even cause a very slow burn in the stored harvest. As an experiment, I bought a couple of bags of pure alfalfa pellets and worked them into the compost pile. I didn’t pay much attention to the pile afterwards until just before Christmas when, amazingly, steam was rising off the compost pile! And the temperature was -12 C! I had to know what was going on and took a fork and opened it up to make sure it wasn’t burning. It wasn’t, but the steamy, earthy smell coming from the compost pile was rich and a little bit like rotted manure mulch. The insulating effect of the snow and the microbial activity of the alfalfa on all the vegetable matter in the clippings pile had brought the temperature in the pile up to a point where if felt very warm to my hand. I covered it back up and let it do its work.
In the spring when we were looking for potting soil to start our plants I went straight to the spot where the alfalfa had been mixed in. The compost was complete wherever the alfalfa had been mixed in! Even the clippings from the last fall were composted to a nice loamy mix.
Later, when all the snow had left, I spread alfalfa pellets over the remainder of the yard clippings compost pile and rototilled them in. Now, the work of converting to useable compost is done in months rather than years!
Needless to say, alfalfa pellets are mixed liberally into our clippings pile each time we use the lawn sweeper.