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Composting and Mulching

by James B. “Jim” Kea
Area Extension Forestry Agent – now retired
Thursday, February 9th, 2006

Yard waste from recent hurricanes could easily overwhelm county landfills. Home owners can greatly reduce this burden on county services by composting these materials or using these materials as mulch.

Composted organic matter can serve as a minor source of nutrients, but more importantly as a soil amendment. As a soil amendment, organic matter, in the form of humus, turns sandy or sandy clay soils to rich loamy soils. As a source of nutrients, it takes over 500 pounds of leaves to equal one 50 pound bag of 8-8-8 fertilizer. Loamy soils remain moist, but well drained, while allowing for good aeration which is as important as moisture. Humus holds on to nutrients like a magnet. This hold is strong enough to keep water from washing the nutrients away while not too strong for roots to absorb. Humus also provides food for beneficial organisms that not only help to further break the organic matter down, but also form a unique relationship outside and inside the tiny root hair that greatly increases nutrient uptake. Humus will not turn wet, mucky soil into loam. Sand must be added to these soils to increase aeration and drainage.

Organic matter can be composted to the crumbly, humus stage in as quickly as two weeks or as slowly as two years. Rapid composting requires lots of organic matter, moisture, nitrogen, air, heat and several small plants and animals to shred and digest the organic matter. Organic matter could include leaves, pine straw, saw dust, wood chips from right-of-way maintenance, peanut hulls, kitchen waste, corn cobs and husks. Do not include walnut, cherry leaves or other plant parts that may be toxic to other plants or diseased plants. Newsprint may be shredded and added, but not glossy, magazine type paper. The ink may contain chemicals toxic to plants. Small amounts of animal or vegetable grease or oil can be added if it is well mixed with fine sized organic matter such as corn meal. Such a mix is used by commercial fishing worm operators. Nitrogen sources could include grass clippings (avoid seed heads), green leaves or needles, blood meal, cottonseed meal, manure, or chemical fertilizer. The more nitrogen added, the faster the breakdown will occur.

The bulky organic matter and nitrogen source should be piled in a bin or container at least 4 feet by 4 feet by 4 feet tall. A piece of 2X3 inch galvanized wire five feet tall and 25 feet long forming a circle works well. It can be unhooked and moved when turning a pile or used for another pile. Shredding the bulky material will speed up the breakdown.

For fast breakdown, mix the material well at about three parts bulk to one part organic nitrogen (fresh manure or green plant parts) and add enough water as you mix to moisten the pile. One cup of 10-10-10 chemical fertilizer per 20 cubic feet of bulky material can be substituted for the organic nitrogen. Too much water will cause the pile to sour. Souring may produce material toxic to plants. Ammonia indicates souring. The pile should be turned and thoroughly mixed after three or four days. Heat should be felt in the pile as organisms use the nitrogen to break down the organic matter. The more nitrogen, the faster the process. Too much nitrogen may cause the pile to smoke, steam, or even burn. Cool the pile with water and mix more bulk if the process is too fast. Chemical nitrogen is a salt and should be used for the slower process. High heat in the pile will kill some weed seed and some organisms.

For the slower breakdown, simply pile material in the wire bin as it becomes available. Break limbs and branches into two foot sections. Pack the pile and water if material is dry. Add layers of soil to pack the pile. Add kitchen vegetable scraps and egg shells. Turn the pile at least every six months mixing materials while turning. Spray extremely dry material with water. More frequent turnings will speed up breakdown. Remove the wire to form another pile as soon as the pile settles. After two years either use the pile in the garden or mix it with new material. Any limbs not completely broken down can be thrown into the next pile. Bins can hold a great deal of yard waste. Volume should drop in half between turnings. Year-old piles make excellent potato beds.

The end product with either method will be a dark, crumbly material similar to peat. As compost gets older, it will lose nitrogen. It can be mixed into soil after being applied one half to one inch deep. A liquid fertilizer can be made by soaking compost in water for several days until a weak looking tea is produced. Pour about one pint of the tea around transplants. Compost can also help reduce the pH of areas overly limed. The relatively low pH of the compost will dilute the lime and neutralize its chemical effect.

Organic material can also be used in its uncomposted state as mulch. Mulch will eventually decompose to the humus stage, but will provide weed control, protect soil from compaction, control erosion, and conserve moisture in the mean time. Mulch should be sized between a dime and a silver dollar to allow water and air to move freely through to the soil. Two to four inches in depth is sufficient to stop most weeds. Avoid materials that will crust over. Saw dust and whole leaves can seal the soil. Also adjust the mulch thickness if soils become too wet or too dry. Mulch areas under trees and in walks where grass won’t grow. Save clean pine straw in early fall to cover mulched leaves in early spring. The clean straw will go further and the leaves won’t blow or be unsightly. Mulches will increase populations of slugs and millipedes. These “pests” help breakdown organic matter into smaller particles. Some strange looking mushrooms may also appear. If problems exist with these pests, thin out mulch or move away from areas where conflicts occur.

Wood ashes may also supplement or replace store bought nutrients. A cord of wood will produce about one bushel of ashes. Ashes contain from 20 to 50% lime as calcium carbonate, about 5% potash and very small amounts of phosphorous. Lime in the ash is rapidly available to plants because of its oxide form and small particle size. Ashes from dense hardwoods such as hickory and oak are higher in lime and potash content than pine or gum. Use wood ashes at the rate of 25 pounds per thousand square feet or lightly dust a layer of ashes every 6-8 inches in your compost pile (two cups for 20 cubic feet of bulky organic matter). Do not use ashes or lime on acid-loving plants. Ashes mixed with water will produce a very caustic material (lye) that will burn flesh and corrode metal. Use care to keep out of eyes and off skin. Water in thoroughly after spreading. Wash ashes from cars or other painted surfaces. And by all means use only cold ashes. Run soil tests on areas before adding ashes and have compost tested to check for pH. The materials for soil testing and the test itself are free.


Revised 2/16/2006.

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