LARRY SUTTON

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August 16, 2014
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Ask A Master Gardener: How do I build a compost pile?

Q. We are considering adding a compost pile to our back garden. What do we need to do to create one that is safe and looks good?

A. Composting is the gardener’s ultimate recycling. Almost everything that has come out of your yard or garden can be recycled. Yard waste is an ideal source for raw materials for your composting. Nature; including microorganisms, worms and other creatures recycle the nutrients into carbon dioxide and rich soil which you can reapply to your garden or yard.

Composting can be broken down into two separate approaches known as cold and hot composting. The cold method is slower and comes about when ideal conditions are not maintained in your compost pile. The decay (recycling) is slower and does not reach the temperatures needed to kill the pathogens (diseases) or the weed seeds that you have put in your compost pile.

Hot composting is fast and healthy. All you need to do is create a balance between the food, water and air in the compost pile. When in balance the interior temperatures of the pile will rise rapidly to between 120 F and 150 F. The bad things in the pile are killed and the fungi is not impacted. Once the heat phase has been completed, worms, insects and other decay-causing creatures move in to complete the decay.

Food for your compost pile is composed of energy materials, bulking agents and balanced raw materials. Below are suggestions for each of the categories.

Energy Materials

(High moisture, low porosity, high nitrogen)

• Grass clippings

• Fresh dairy, chicken or rabbit manure

• Fruit and vegetable waste

• Garden trimmings

Bulking Agents

(Low moisture, high porosity, low nitrogen)

• Wood chips

• Sawdust

• Grass Hay

• Corn stalks

Balanced Raw Materials

(Low to medium moisture, medium porosity, medium nitrogen)

• Ground up tree and shrub trimmings

• Horse manure and bedding

• Deciduous leaves

• Wheat straw

• Legume hay

You should mix your compost pile with two parts bulking agents to one part energy material by volume. Avoid adding woody branches as they will decompose slowly and make it difficult to turn your pile. To effectively hot compost you need to have a uniform size of raw materials. Ideally you would run all your materials through a chipper/shredder before adding them to your pile because small particles provide more surface area for the microbes to attack and also makes it easier to turn. Thoroughly mix the materials when you start the pile. If new materials are to be added later on, place them in the center of the pile. This will aid in the aeration and prevent anaerobic activity. The material in the center of the pile should feel damp but not wet.

The minimum size pile to ensure good heat buildup is one cubic yard. Small piles tend to be colder and will dry out faster. There is no maximum pile size limit. A good rule of thumb is to build your pile no higher than you want to turn. As your material starts to decompose it will settle and become denser or heavier. This reduces aeration. Turning the pile and or adding more bulking material keeps the aeration working.

Some items should never be added to your compost pile. Meat, dairy, and grease lead the list of items not suitable. Human and pig manure contain pathogens that can and will pass on diseases. Go light on wood ashes. While they are a good source of lime and potassium, they can radically impact the pH of your soil. Add no more than one cup per bushel of compost. If you have used weed and feed fertilizer on your lawn, do not use the lawn clippings until at least the third mowing. It is OK to let the grass clippings from the first two mowings drop to the ground and decompose in place.

You do not need a bin or an expensive container to make your compost. Some people prefer a simple pile while others go for a bin. Bins are available commercially. Bins can be constructed with cinder block, wood or even bales of straw. Choose the one that most fits your life style. The compost area of the Master Gardeners Discovery Garden has on display a representation of both commercial and home-built composting bins.

You can use your compost materials to add organic material to your soil by simply mixing the two together. It can also be used as a mulch to help control weeks, reduce water consumption or prevent erosion around your existing plants.

Do you have a gardening question? Please email, call or visit the Douglas County Master Gardener Plant Clinic at douglasmg@oregonstate.edu, 541-672-4461, or 1134 S.E. Douglas Ave., Roseburg.

Douglas County Master Gardeners are trained volunteers who help the OSU Extension Service serve the people of Douglas County.


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The News-Review Updated Aug 16, 2014 12:06AM Published Aug 16, 2014 12:06AM Copyright 2014 The News-Review. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.