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Revised 10/02 Purdue University Cooperative Extension Service Page 1 of 3

Solid Waste Management Series . ID-182-W

Department of Horticulture

Purdue University Cooperative Extension Service • West Lafayette, IN

Managing Yard Wastes: Clippings and Compost

B. Rosie Lerner

Turning Trash to Treasure

Yard waste materials such as grass clippings, leaves,

and yard trimmings make up approximately 10% (by

volume) of the municipal waste stream, according to

Indiana’s Department of Environmental Management.

Yard waste can account for 50% or more of residential

solid waste during the active growing season.

Although this waste is biodegradable, landfills do not get

the oxygen and water needed for breakdown. Landfills

are constructed to prevent movement of air and moisture

in order to protect the surrounding environment. These

materials can be better put to use enhancing our gardens

and landscapes.

Some communities have established municipal

composting facilities to efficiently manage large quantities

of yard wastes. But by reducing the amount of yard waste

generated and recycling the rest, gardeners can have a

great impact, both economically and ecologically.

Reducing Yard Wastes

Leaving grass clippings on the lawn rather than bagging

for disposal is an excellent way to dramatically reduce

yard waste. The amount of grass clippings generated

from a given lawn varies, depending on the grass species,

weather, fertilization program, and yard size. One

estimate indicates that 5,000 square feet of lawn generates

about 1 ton of clippings per year!

Grass clippings left on the lawn are not harmful to the turf

if it is mowed at the proper height and frequency. In fact,

the clippings will return some nutrients back to the soil,

reducing fertilizer requirements. Contrary to popular

belief, grass clippings do not contribute to thatch buildup

because they break down quite rapidly. Thatch is composed

of dead, decomposing roots, and underground

stems.

Maintain the lawn at a height of about 3 inches, removing

no more than 1/3 or the grass plant each time. This will

likely mean mowing more often than once a week, but

mowing time is greatly reduced when clippings are not

collected. Mow only when the lawn is dry to prevent

clippings from matting down. If the lawn is excessively tall

when mowed, you should remove the clippings and either

use as a mulch or add to a compost pile.

Recycling Yard Wastes

Composting is a naturally occurring process that breaks

down organic materials into a soil-like material. Finished

compost is an excellent soil amendment that improves

soil structure as well as adds some nutrients. All organic

materials will break down eventually, if given the proper

environmental conditions. Gardeners can speed up the

composting process with proper management of the

materials and environment of the compost system.

Ingredients of Compost

The basic ingredients for successful composting include

organic materials, microorganisms, and the proper

balance of carbon to nitrogen, water, and oxygen. Let’s

look at each of these more closely.

Organic materials for composting include discarded

garden plants, grass clippings, tree leaves, and plant

trimmings. The smaller the particle size, the faster the

organic materials will break down. Materials which have

been chopped or shredded will compost more quickly.

Kitchen wastes such as vegetable and fruit scraps, egg

shells, and coffee or tea grounds can also be added.

These materials should be buried in the center of the

compost pile to avoid attracting insects, rodents, and

neighborhood pets.

Some organic materials are best left out of the compost

pile because of possible health hazards or attractiveness

to pests. Because of the danger of disease transmission,

human and pet feces should not be composted. Meat

scraps, bones, and fats will likely attract rodents and

other unwanted visitors.

Less experienced composters should avoid materials

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Solid Waste Management Series . ID-182-W

heavily infested with weed seeds, insects, and disease

organisms. Although a properly managed compost pile

should generate enough heat in the center to kill most of

these pests, ensuring uniform heat may be difficult,

particularly in a small compost pile.

Microorganisms (microbes) such as bacteria and fungi

are responsible for breaking down the organic materials

in yard waste. Although commercially packaged compost

starter is available, adding a little soil or finished compost

will supply all the microbes you need for composting.

Microorganisms require a proper environment to work

efficiently. Any factor which affects the microbial population

will also affect the rate of decomposition.

Nitrogen is needed by the microbes in order to break

down and use the carbon found in organic materials. The

ratio of carbon to nitrogen in the compost pile will affect

the rate of decomposition. If the carbon content is too

high, decomposition will be slow. If the nitrogen content is

too high, ammonia gas can be given off, creating foul

odors.

The ideal ratio of carbon to nitrogen is approximately

30:1. Table 1 shows the carbon to nitrogen ratios of

various organic materials. Sawdust has a high C:N ratio,

while animal manures have a low C:N ratio. The ideal

ratio for composting can be achieved by combining high

and low carbon materials, such as dry tree leaves and

fresh grass clippings. Another method is adding a

nitrogen source such as livestock manures or commercially

packaged fertilizer to high carbon materials.

Water is also needed for efficient microbial action and

uniform heating of the compost. Apply water as needed if

rainfall is lacking. Compost with optimum moisture

content should resemble that of a moistened sponge that

has the excess water squeezed out.

Oxygen is required for efficient decomposition and to

prevent foul odors. Breakdown occurs more slowly when

oxygen is lacking, and foul odors from fermentation will

result. Turning and mixing the pile at least once or twice

a month will add oxygen from the air into the center of the

pile. Mixing the compost also helps bring the outer

materials to the center for heating and faster decomposition.

Lime is generally not needed in most compost piles.

Although lime is recommended by some gardening books

to "sweeten" (make alkaline) the compost pile, several

studies indicate that finished compost is already slightly

alkaline. Adding lime may lead to production of ammonia

gas, which allows nitrogen to escape from the pile and

causes foul odors. Wood ashes are very highly alkaline

and should only be added in very small quantities, if at

all.

Containing Compost

Compost can be constructed in open piles, but it is

probably more easily managed in some type of structure.

Many types of containing materials can be found around

the home or at a hardware supplier. Examples include

wooden pallets, metal mesh wire, and cinder blocks.

Molded plastic bins such as those with a turning crank

and aeration holes are also available for relatively small

composting operations.

A three-bin container is ideal for managing compost

(Figure 1). One bin is for actively composting materials.

One bin remains empty to allow the compost to be turned

over more easily. The third bin is used for holding plant

materials until the current compost is finished.

Locate the compost pile close enough to the house so it

is readily accessible but out of the way of other activities.

Choose a shady spot with protection from the wind to

avoid excessive heating and drying.

Managing Compost

To achieve a good balance of materials, construct

compost piles in layers, alternating yard wastes; a

nitrogen source, if needed; and soil (or finished compost)

(Figure 2). The base layer should consist of 6-10 inches

of organic materials, with coarser, dry materials on the

bottom. If needed, follow with a nitrogen source such as

3'-5"

3'-5"

4'-5"

Empty Active Holding

Figure 1. A three-bin

container for managing compost.

Table 1. Approximate carbon to nitrogen (C:N) ratio of

various materials used in municipal and backyard

composts.*

Material C:N ratio

(wt:wt)

Livestock manure 10 to 30:1

Table scraps 11 to 15:1

Alfalfa 12 to 19:1

Grass clippings 15 to 25:1

Fruit wastes 25 to 45:1

Sugarbeet 30 to 40:1

Leaves 40 to 80:1

Paper 200 to 800:1

Sawdust 100 to 750:1

Wood 200 to 1300:1

*Adapted from Composting and Mulching: A Guide to

Managing Organic Yard Wastes. University of Minnesota

Extension Service Bulletin BU-03296.

Revised 10/02 Purdue University Cooperative Extension Service Page 3 of 3

Solid Waste Management Series . ID-182-W

1-2 inches of animal manure or approximately 1 cup of a

balanced, low-analysis fertilizer (such as 12-12-12), per

25 square feet of compost surface area. The next layer

should be approximately 1 inch of soil or finished compost.

Repeat layers as organic materials are added.

Water each layer as it is needed, and check the pile

occasionally for watering needs.

The center of a properly managed compost pile will

generate heat as the microorganisms break down the

organic matter. A good-sized compost heap, approximately

4-5 feet in diameter and 4-5 feet deep, should

reach 130° to 160° F in the center.

Turn the pile with a pitchfork or shovel at least once or

twice a month to keep the materials supplied with oxygen

and to bring outer contents to the center for heating.

Small amounts of organic materials can be added to

actively composting piles, but it’s best to start a new pile

when compost becomes too tall to work by hand.

Using Finished Compost

Compost can be ready to use in as soon as a month or

as long as a year, depending on how well the pile is

constructed and tended. Finished compost should look

much like a uniform potting soil, with no indication

remaining of what materials originally went into the pile.

Compost can be used as a soil amendment in the garden

to add some nutrients, but its primary advantage is that of

improving soil structure. Adding compost increases

water-holding capacity, aeration, and nutrient exchange

sites in the soil.

Compost can also be used as an organic media in potting

soil or for starting seeds of garden plants. Finished

compost is free of pests and weed seeds only if it has

been properly mixed and uniformly heated. To be sure

your compost is free of pests, pasteurize it by heating in

a conventional oven to 180° F for 30 minutes. Be sure

the compost is slightly moist to ensure uniform heating.

Compost is also useful as a garden mulch to conserve

soil moisture, cool the soil, and discourage weeds. And it

can be used to cover seeds as they are planted, to

prevent crusting in heavy soils.

Compost is an inexpensive and ecologically sound

Less coarse organic material

Coarse organic material

Soil or finished compost

Manure or fertilizer

Figure 2. Compost constructed in layers.

Because of possible injury to desirable plants,

clippings from lawns treated with weed killer should

not be used as mulch for at least 8 weeks after the

herbicide is applied. Most commonly used lawn

herbicides will break down in that time, but some do

take several more months to a year to degrade.

Leaving these clippings on the lawn is the best

method of disposal.

Pesticides are biodegradable and are dependent on

the same environmental factors as composting yard

wastes: microorganisms, temperature, water, and

oxygen. Several studies have shown that

composting decreases the concentrations of most

modern-day pesticides to levels below EPA regulations.*

* Mechanisms of Pesticide Degradation in Compost

By Craig Coker, Composting Specialist

North Carolina Division of Pollution Prevention &

Environmental Assistance

http://www.cra-recycle.org/CCC/techcornerindex/

techcornerarticles/TCpesticidedegradation.htm

A citizen education program called "Don’t Bag It"

was piloted in Ft. Worth, Texas to encourage

citizens to reduce yard waste. The 184 residents

participating saved the city $60,000 in garbage

collection costs and saved themselves a total of

$22,000 by purchasing fewer plastic bags for

disposal. Participants reduced the average time for

mowing by more than 30 percent, although they did

mow more frequently. And, of course, the local

landfill saved considerable waste space.

"Don’t Bag It" Lawn Care Plan, Texas A&M

Extension Service

http://aggie-horticulture.tamu.edu/extension/

homelandscape/dontbag/dontbag.html

For more information on the subject discussed in this

publication, consult your local office of the Purdue University

Cooperative Extension Service.

It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to programs and facilities

without regard to race, color, sex, religion, national origin, age, marital status, parental status, sexual orientation, or disability. Purdue University is an Affirmative Action employer.

This material may be available in alternative formats. http://www.agcom.purdue.edu/AgCom/Pubs/menu.htm

method of managing yard waste and producing an

excellent gardening tool. Composting will help you

recycle your garden wastes, improve your soil, and

reduce disposal costs