In fact, University of Maryland recommends that a gardener add six inches of compost to new gardens for several years and one inch of compost to established garden every year. While compost does not have high NPK values, it improves the soil structure of any type of soil. In my Howard County clay, compost aggregates the small clay particles into larger particles which permit more air to permeate the soil and increase water drainage. In sandy soils, compost holds moisture and retains nutrients in the soil. Information on soil fertility and composting can be found on the University of Maryland's HGIC website. The links are soil fertility and conditioners and composting.
I have five compost bins made up of four foot oak pallets rescued from the Howard County dump, wood waste facility. They are always in use since I stockpile my browns (leaves) for use throughout the spring and summer.
While the green season is mostly over, I am still harvesting some grass clippings, garden and kitchen waste for addition to the browns I am collecting through the Howard County Master Gardener Rake and Take Program. Rake and Take Later this winter, I will be adding manufactured nitrogen in the form of urea. I run hot compost piles all winter long and with a carbon to nitrogen ratio of 25 to 1, the piles will heat up to approximately 160 degrees regardless of the outside temperature.
I regularly collect 2 to 3 hundred bags of leaves during the fall which are used to create about 7 cubic yards of compost for my 2,000 square foot garden. It takes me around 3 or 4 months to produce about a half yard of leaf compost from my one and a half yard compost bins.
My most recent piles were started using equal weights of leaves and grass clippings mowed from my lawn. A spreadsheet showing the ratios for greens and browns can be found at this link. The Carbon to Nitrogen Ratio spreadsheet is listed on the right side of the page under useful links.
Browns and greens are mixed together (I find this more effective than layering) and added to the bin along with some moisture which I add using a syphon mixer, a five gallon bucket and a water breaker. Fall leaves are very dry and the microbes which break down the browns like a damp medium. I use the syphon mixer to add a water/detergent mixture (surfactant) from the bucket to the hose stream. The surfactant lessens the surface tension of the water and allows it to coat the dry leaves.
After about ten days, the compost needs to be turned into an empty bin to renew its oxygen supply. My main turning equipment is a mini tiller and a pitchfork.
The mini tiller does a wonderful job of breaking up the matted leaves and adding air to the compost mix. Then it is a matter of forking the mixture into an empty bin. As the browns start to break down, the microbes will use up the available nitrogen in the mixture. After 8 to 12 weeks of turning and transferring the compost between bins, the temperature of the pile will decrease as the browns breakdown and the available nitrogen is used up. Once the pile no longer generates heat, allow it to age for about a month. After aging, the compost is ready to be used in the garden. Some people screen their compost to remove the larger uncomposted material, but I just use it as it comes out of the pile.
Winter is a great time to add compost to your garden beds. While you're at it, do a soil test if you haven't done one in the last three years.
Compost is truly black gold and will increase the productivity of your garden. In fact, I have been accused of being a Miraclegro gardener, when in fact it's the black gold which improves soil structure holding water and nutrients in the soil permitting plants to reach their optimum potential.