The GIEI recommendation for established gardens is to add an inch of compost to the garden each year. For new gardens, the recommendation is to add 6 inches the first year and several years there after in order to build up a reserve of OM in the soil. If your soil test shows the percentage of OM, your objective is to get the OM % in your soil above 4%. Soils with high OM percentages (greater than or equal to 4%) provide residual nitrogen (N) to plants throughout the summer as the microbes in the soil digest the OM, releasing N and turning the OM into humus. Soils with high OM percentages release some N and can reduce the amount of fertilizer needed for each crop. The higher your OM percentage, the more N will be release during the warm weather when soil microbes are active.
During cool weather, spring and fall, you will still need to fertilize your crops at planting time (.2 of a pound of N per 100 square feet) and when side dressing plants. Side dressing recommendations can be found under each crop profile on the GIEI website..
Throughout the gardening season, I add additional compost to those areas where a second or third crop is being planted. As I empty a bin, I reload it with an 30 to 1 mixture of browns and greens.
The four ingredients needed to hot compost are an appropriate mixture of carbon rich materials like leaves or other dead plant material (browns) and nitrogen rich materials which are living/green plants, vegetable waste from the kitchen or if they are not available, a nitrogen rich fertilizer like urea (greens). The appropriate ratio of browns and greens is a 30:1 ratio. To determine how to create a 30:1 ratio of brown to greens, you can either wing it or refer to the carbon to nitrogen ratio spreadsheet on the Howard County MG composting website. Just click on the link on the right side of the page and enter the approximate weights of the browns and greens you have and adjust those values to reach a ratio around 30:1.
For example, this fall I was mixing 100 pounds of dry leaves with 160 pounds of grass clippings. to create a 30:1 mix. As I mix these two materials together, I wet them down so that the mixture is about as damp as a rung out kitchen sponge. I continue adding browns and greens, mixing and wetting until my pallet bordered bin is full.
I have a five bin system, made up of recycled oak pallets that I select from the wood waste pile at the Howard County landfill. These bins are about 4 by 4 feet, but in the winter you will need at least a 3 by 3 foot bin to retain the heat built up as the microbes start the decomposition process. Pallets last a couple of years before they start to rot, at which time I cut them up and burn them in my fireplace. When loading the bins, I always leave on bin empty, so that I have someplace to turn a loaded bin into. Another trick I learned several years ago is to cover my winter piles with a sheet of plastic to keep excess moisture out. I also insulate the top of the pile by covering it with bags of dry leaves.
After loading the bin, the aerobic decomposers start to work, they use the N from the greens, oxygen and moisture to breakdown the carbon rich materials. This process produces lots of heat. When first started, the pile should heat up very quickly (2 days) and reach between 140 to 160 degrees. The picture shows a 6 inch instant read thermometer in a pile I recently started.
After about a week, the temperature in the pile will have declined and the pile will have shrunk in size. At this point, the bacteria and other aerobic decomposers will have used up oxygen in the pile and the pile needs to be turned to introduce more oxygen and check for the moisture content (Pile should be as damp as a wrung out sponge.). Breaking up a matted down pile can be difficult, especially if you are composting leaves that have not been shredded I use a mini tiller, place it on top of the pile and use it to breakup the pile. A word here about shredding leaves, which is not necessary. However, the smaller the particle size you start with, the faster the materials will decompose, but the pile will mat down faster and may have to be turned more often.
After turning the pile out, I just fork it into the next bin. During the first four weeks, the pile will need to be turned weekly and it will continue to reach very warm temperatures since it will contain a good amount of green material or nitrogen to act as fuel for the bacterial. As the fuel is used up, turning the pile to introduce oxygen won't cause the pile to heat up as much because a large portion of the nitrogen in the pile will have been used up. After about 8 or 10 weeks, turning the pile won't produce any temperature increase and the pile should be left to mellow for 4 weeks. After that period of time, the compose can be used.
The University of Maryland's Home and Garden Information Center has a publication on Backyard Composting. If you would like to learn more about composting, you can always visit one of Howard County MG compost demonstrations sites during the summer to learn more. Date and times for the compost demonstrations can be found on the Howard County GIEI class schedule.
If you are like me and can't produce enough compost to fulfill your gardens requirements, high quality compost is available at Howard County's Alpha Ridge landfill. This pilot composting facility produces high quality compost from yard trim (grass, leaves, etc) and food scraps collected and delivered to the facility. Lab tests are conducted on the compost to insure it meets EPA limits on metals and to insure that it is mature compost with no residual herbicides contamination.
So clean up your gardens this winter, load your compose piles and wait for the seed catalogs so that you can plan for the 2016 garden.