Compost

Adding compost to soil increases the level of microbial activity and helps plant roots absorb nutrients. The organic matter helps improve soil structure, water retention, and aeration. Plants grown in soils amended with compost tend to be healthier, have increased drought tolerance, and are more resistant to some pests and diseases. It also improves soil chemistry, so nutrients are more available to plants. Many micronutrients are chemically bound up in the soil which makes them unavailable to plants.

Compost provides food for earthworms to live and multiply. Earthworms, in turn, help aerate the soil and their castings contain nutrients plants can absorb. Composting decreases the amount one needs to spend on soil amendments and will lessen the need for fertilizers.

Composting turns garden waste, kitchen vegetable and fruit scraps, and other organic material into a valuable soil amendment and plant fertilizer. It has been practiced for thousands of years and is still widely used throughout the world by gardeners and farmers. The chemical process necessary to turn garden trimmings and kitchen scraps into good compost requires carbon, nitrogen, water, oxygen, and microorganisms such as bacteria and fungi. NOTE: Check with your school district as some prohibit the use of home-made compost.

Compost Materials

For the composting process to work effectively, material to be composted should have a carbon to nitrogen ration of 30/1. This cannot be measured easily, but experience has shown that mixing equal volumes of natural dry plant material (carbon) and green plant material (nitrogen) will give approximately a 30/1 carbon to nitrogen ratio.

Materials high in carbon, referred to as “browns”, include such materials as dried brown leaves, straw, woody stems, bark, mixed paper, newspaper, cardboard, wood chips or sawdust. Materials high in nitrogen, referred to as “greens”, include vegetable and fruit scraps, coffee grounds, green leafy material (grass clippings, fresh pruning material, and weeds that have not gone to seed), corn stalks or tomato stems (shredded or cut into small pieces).

If a material is green when it is cut or harvested, it will lose some nitrogen if left to dry out before shredding, but it is still considered “green”. Leaves that have fallen from a tree, as in autumn leaves, are mainly carbon because the nitrogen has returned to the roots due to the shortening day length and cooling temperatures.

Waste products that should never be added to your compost pile include:

    • Animal feces from dogs, cats, and other carnivorous animals.
    • All manures other than commercially processed bags.
    • Ashes.
    • Weeds that have already formed seeds.
    • Diseased plants.
    • Dairy or meat products.
    • Bones, fish, lard, mayonnaise, peanut butter, oils, and bakery goods which may attract critters and take a long time to decompose.
    • Palm fronds which are too fibrous, difficult or impossible to shred, and require too much time to decompose.
    • Walnut husks and walnut leaves which take too long to decompose and inhibit the growth of some plants such as tomatoes.
    • Rose clippings – because of the thorns.

Making Compost

There are two basic methods for making compost: passive and active. Passive composting is as simple as collecting organic waste, placing it in a pile or bin and periodically spraying with water to keep the material moist. Over the course of a year or so, the material will decompose. Active composting is a faster process obtained by creating optimal conditions for decomposition to occur. You’ll get compost in one to three months during warm weather. Several things are required for rapid “hot” composting: nitrogen (greens), carbon (browns), air, water, small sized material (hand size or less) and building a large enough pile to retain heat (at least 3 x 3 x 3 feet). Together, these components feed microorganisms, which speeds up the process of decay.

Passive Composting

Passive composting requires little effort. Brown and green raw materials are placed in a pile in proper proportions, and occasionally watered and turned to keep it moist until the material is no longer recognizable as leaves, grass or vegetables. Such a pile is usually built gradually, adding material a little at a time. The smaller the particle size, the faster the material can break down. Mulching mowers can help shred plant materials and leaves; chipper/shredders can reduce the size of large material, but both are expensive and require storage space.

Passive compost piles that are relatively cool, often harbor insects such as spring tails and beetle larva, nematodes, fermentation mites, centipedes, millipedes, sow bugs, pill bugs, and earthworms, which assist in the decomposition process.

Some less desirable creatures, such as flies, ants, earwigs, snails, and slugs are also attracted to passive compost piles. To discourage these less welcome creatures try turning and moistening a pile more often. Heat will build up in your pile if the material you use has the proper ratio of carbon and nitrogen. Frequent turning and watering will help maintain higher temperatures, by supplying the oxygen and moisture necessary for complete and rapid breakdown.

Another option is to place the compost material in a commercial compost bin, add water, and stir occasionally. Finished compost is removed through the bottom door as it appears ready for harvesting.

Active Composting

The active or hot composting method is more labor intensive, but it is also much faster. Under optimum conditions it is possible to have beautiful brown compost in just a few weeks. Begin by building a large enough compost pile all at once by layering green and brown materials and watering as you add the material. Every few days, or weekly, turn the whole pile by forking it from one place to another (or from one bin to another). Water it as you turn it so the material will be as damp as a wrung-out sponge. When turning the pile, place material from the outside of the old pile into the center of the new pile.

The optimum size for a compost pile to heat up properly and maintain the temperature is at least 3 x 3 x 3 feet and not larger than 5 x 5 x 5 feet. If using a compost thermometer, the pile should be turned if it reaches 150°F or higher, or if it cools to below 100°F. The aeration and moistening will enable the pile to heat up again. A temperature of 140°F for a 21-day period is required to kill most seeds (except for tomato seeds) and disease pathogens. If you have too little nitrogen and your pile won’t heat up, you can add a small amount of nitrogen fertilizer, such as ammonium sulfate or blood meal, to your pile when turning. If there is too much nitrogen, there will be a strong odor of ammonia, but adding a little sawdust or shredded paper when you turn the pile can help.

Vermicomposting

Vermicomposting uses red worms, also called red wigglers, to help digest decomposing material. When worms eat the food scraps, they release “castings” that contain nitrogen and other plant nutrients. You can purchase red worms inexpensively online or at a garden supplier. Earthworms usually found in garden soil are long lived, but do not multiply fast enough to use in a worm bin.

Worm composting is generally done in manufactured worm bins, but can be done in wooden boxes or plastic storage boxes as well. Newspaper torn into narrow strips and moistened, can be used as bedding material and then worms are added along with a small amount of compost material.

When making a worm bin from a plastic storage box, choose one that is opaque, if possible. Using a drill, make about twelve 1/4 inch holes in the bottom of the box to allow the worm liquid (“worm-tea”) to drain. If the liquid does not drain out, the bedding will get too wet and the worms will try to leave or may drown. Purchased worm bins usually come with bedding material. With a three layer box system, the bottom section will catch and hold the “worm tea”.

Kitchen green waste is added every few days. To add new “green” material, put on plastic gloves and pull the worm castings to one side of the box; add the green materials; then push the castings back over the new material. The next time, pull the material from the opposite side of the box, add the material and cover it over, as before. For more detailed information go to the Worm Care Guide.

The worms will multiply in the bins and over time the castings can be harvested and used in the garden as a soil amendment and plant food. Worm castings should be mixed with soil at a ratio of 10 parts soil to one part worm castings. Worm tea should be diluted 6:1.

Worm bins should be kept in a shady location. Direct sun on the worm bin can “cook” the worms. Add new material only after the previous material has been well digested. If too much material is added at one time, or so frequently that it is not digested, the box may become smelly. In that case, do not add more material for a week. Or you can add some finely shredded paper (carbon) and gently mix it into the castings, then wait a while before adding more green material.

At some schools the cafeteria saves the green scraps from preparing lunches for use in the worm bins. Not all school districts will allow this, so check to see if this is possible at your school. You can post a sign to remind students that meat products, cheeses, fried foods, oils, and fats, should not be put into the worm bins. These materials tend to attract unwelcome critters (raccoons, dogs, and cats). The worms do not “eat” the waste products; rather, they digest decomposing materials.

Compost Resources

For more information on composting go to: