This section on composting covers the gamut of backyard composting (rather than commercial) tips and techniques.
What is compost?
Compost is the finished end product of the process of decomposition of organic matter, whether plant, animal or a mixture. Compost is the decomposed remnants of plants -- whether it is leaves, stems, flowers, fruits, and thick hard cellulose fibers such as bark and wood. Animals and animal manures can be termed composted material as well.
For the home gardener, compost is typically decomposed plant debris from our gardens: grass clippings, autumn's fallen leaves, pruned stems, limbs and branches, unwanted, spent or dead plants, and vegetables, fruits, and kitchen scraps.
Sometimes compost is referred to as humus. Humus is a complex substance, the end product of decomposition. Organic matter that has been acted upon by soil bacteria and fungi are converted into a mixture of complex compounds of gums, starches, plant waxes and lignins. Humus is categorized as active and stable, really a continuum that ranges from fresh decomposed plant material to a solid dark brown granule that resists further decomposition. Throughout the process of decomposition, nutrients are released for the plants, and the stable humus aids soil structure. Healthy soil contains organic matter, or humus, in all stages along the continuum, each stage providing benefits. Adding just the granular, stable humus is beneficial, but the constant and steady decomposition of organic matter is essential to healthy, vigorous plant growth.
Not all plants need the same amount of compost. The usually rule of thumb is, the more water a plant requires, the more nutrients it needs as well. Xeric plants, needing significantly less water that high water-use plants, also require less nutrients. Match the soil type, including organic content, to the plants needs.
Benefits of Compost
Even though I've listed the benefits of compost elsewhere in this website, compost is so beneficial, the benefits bear repeating.
- Compost aids in better soil structure by building better crumb structure, or aggregates. In tight, compacted clay soils, compost provides spaces for air and water, allowing air and water to circulate easier. In sandy soils, where water and nutrients drain away too quickly, the fine sand particles are built into large crumbs that hold water and nutrients. The higher the humus content, the greater the moisture absorption. This provides bother better retention and drainage.
- Compost holds soil together better in a more desirable structure due to the sticky gums and resins secreted by microbes through the process of humus formation.
- Compost promotes the growth of mychorrhizal fungi, the beneficial fungi that grow in decomposing organic matter. Increases growth-promoting fungi, which help control diseases, root rot, and damping off fungi.
- Compost lessens soil erosion.
- Compost balances the pH of the soil. Balancing the pH of the soil allows for better mineral absorption.
- Earthworm populations increase in well composted soil.
- Compost helps to conserve water. When ample minerals and nutrients are available, plants require less water for their uptake.
- Compost acts as a buffer to chemicals, reducing toxicity.
- Compost promotes earlier soil warming.
- Compost moderates soil temperatures.
- Compost recycles waste products.
Composting mirrors or echoes the cycle of life and the soil food web. Gardener's don't make the compost, nature does. Gardeners may gather together the materials in an enclosed space and enhance conditions for a more rapid decomposition, but we are not the decomposers.
If a time-lapse camera were to film the action inside a compost pile, we'd probably be amazed at the activity taking place. Most noticeable would be larger insects like rove beetles or centipedes. These feed on springtails, nematodes, and protozoa, that feed on earthworms, bacteria, fungi, actinomycetes, that in turn, feed on leaves, grass clippings, plant debris, food scraps, animal manures and dead bodies of soil invertebrates. A perfect chain that keeps looping around -- also known as the compost food web.
When we think of compost, we probably only think of the brown, earth-like humus, a substance considerably better than dirt that improves the physical structure of the soil. This physical element is important, but even more important is the biological aspect of compost.
Compost is used for the following reasons:
- To add organisms to the soil. Bacteria, fungi, actinomycetes, nematodes, protozoa, microarthropods. Compost serves as an inoculate of all these microorganisms if the compost is made correctly.
- To add foods to feed the bacteria, fungi, actinomycetes, nematodes, protozoa and microarthropods, which in turn feed our plants.
- To add structure to the soil. Many composts contain physical structure components like lignin and other undecomposed woody products. This imparts physical structure that creates air passageways. (Compost Food Web.)
Compost has been termed "black gold" by gardeners. But if we gardeners really understood the importance of compost and its benefits to soil and plants, we would locate our compost piles right outside our back door, in front of the kitchen garden instead of hiding it at the back of the property.
In addition to the biological and structural improvement to the soil, composting is a benefit as a waste reducer. Again, consider the forest example, as we did in the section on Mulch. The plant material: leaves, twigs, stems, cones, spent flowers, plus all the living microorganisms and macro arthropods on the forest floor are a living, continually renewing compost pile. What if we had to gather all that plant debris up and cart it off? And just exactly where would we take it?
Compost happens, naturally.
Composting, Generally Speaking
To compost, you'll need organic material, both brown (carbon) and green (nitrogen), microorganisms (soil and/or manure), air and water. Depending on your carbon to nitrogen ratio, a small amount of nitrogen fertilizer may be added for quicker results, but is not necessary for decomposing. The nitrogen is food for your microorganisms. Air and water create an environment conducive for the microbes to break down the brown and green material. The best composting occurs when your pile heats up 140 degrees to 150 degrees F within five days. As in the soil, too much water or moisture in your compost pile causes oxygen deprivation.
There are many ways to compost and it's always best to do what will work for you. Backyard composting is approached differently from commercial composting operations. Backyard composting is more relaxed, less precise and takes longer. Composting can be an exact science. Compost can be tailor made to fit specific soil and crop needs. Individuals who are interested in maximizing benefits from compost should contact Dr. Elaine Ingham at Soil Foodweb.
For the backyard composter, the act of composting could be as simple as covering vegetable or fruit scraps from meal preparation under a layer of soil. When weeding, just let the weed lie there to decompose, as long as it hasn't seeded out. Or composting could involve an expensive composting device that rotates.
Earthworms are great composters of the world. Decomposing small amounts of material is simply and easily achieved by vermicompositing. Click on vermicomposting for simple instructions of how to use red wriggler worms to compost your household non-meat kitchen scraps in both English and Spanish.
If you have room at all, you should intentionally compost your kitchen and garden vegetative debris (either by vermicomposting or regular composting). If you find it too unsightly to place your compost pile in the place of honor right outside your door, at least make it convenient. You don't have to have a special structure to compost - a pile or area will do. Even just tying together three old wood pallets will work. Small amounts can be composted quickly with little effort, or large amounts composted in several weeks with effort. The principle to remember is to return to the soil what you took from it. The average gardener throws away 40 pounds of nitrogen from grass clippings alone every year when bagging and throwing out lawn clippings (AHS Resource Bulletin No. 112, Compost-- Black Gold).
What to Compost
I compost all my vegetable kitchen scraps, including fruit and vegetables that have rotted in the refrigerator. These materials are commonly composted.
- Egg shells, coffee grounds and tea bags.
- Shredded newspapers or paper.
- Water from cooking vegetables or eggs.
- Fruit and vegetable juices, coffee, and tea.
- Wood chips and pine needles.
- Hay and straw.
- Pruned and clipped plant debris, spent flowers and dead plants.
- Grass clippings and leaves.
- Animal manures from herbivores.
As I cook, clip, prune, deadhead, harvest, mow and rake, I just toss it in, being mindful of whether I need to add soil or manure (for the microbes it provides) or water. Larger pruned branches get set outside my fence for the chipper. If I had a chipper, I'd chip my own branches and add these to the pile, or use them as mulch.
We use a mulching mower, so we immediately return the finely chopped grass blades to the soil instead of composting. This is the easiest method to compost. Mulch mowing autumn's fallen leaves either onto the lawn, or catching them in the mower bag and spreading on flower and vegetable beds is another method of natural composting. The smaller or more finely shredded the material, the faster the decomposing process.
What Not To Compost
These materials are best deposited in the dumpster or not used in the compost pile.
- Diseased, and insect infested plants or plant parts.
- Seedy or rhizomatous material such as Bermuda grass roots.
- Plants that contain toxins that inhibit growth of other plants, such as black walnut leaves, walnuts, castor beans, juniper, acacia, eucalyptus and cypress.
- Do not include any part of poison ivy, poison oak or poison sumac. Do not touch or burn these plants.
- Meat, fats, grease, oils and dairy products can attract rodents.
- Avoid using manure from meat eating pets.
- Do not compost weeds that have seeded out or seeds of weeds unless you are certain the compost pile heats sufficiently to kill them.
- Sawdust, C:N ratio of 500:1 and paper, 170:1. These carbon to nitrogen ratios are too high in a normal compost pile.
- Ashes and charcoal.
- Do not compost herbicides, pesticides or other harmful chemicals or plant parts recently treated with herbicides, pesticides, fungicides, etc.* See below
Most books recommend turning the pile every two weeks for aeration for a rapid turn around. I'm a lazy composter, so I only turn it once every two-to-three months. But my pile takes much longer to compost. I'm not in any hurry; I only apply my own compost once or twice a year. I never have enough for my yard and garden and have to buy extra anyway. Your preferences and needs could be different.
Herbicide Carryover – Killer or Contaminated Compost
Unfortunately, mankind has reached the point of contaminating one of the most natural and beneficial substances, compost. Farmers and home gardeners across the United States have reported damage to vegetable, flower and fruit crops after applying composted manure (whether from cows or horses) or composted hay, straw or grass clippings to the soil. Shortly after these applications as soil amendments or mulch, they noticed stunted growth, poor germination, death of plants, deformed plants and fruit. In most cases, the damage was caused by a group of synthetic chemicals known as pyridine carboxylic acids, sometimes referred to as pyralids, namely, aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr and/or aminicyclopyrachlor. Products containing these chemicals include Curtail, Forefront, Grazon Next, Grazon P+D, Milestone, Redeem R&P, Surmount, Confront, Lontrel, Millennium Ultra Plus and Plus2, Clopyr AG, Stinger and Imprelis. In September, 2009, Mother Earth News reported that a previously considered organic product, Grab 'n Grow, contained one of the above chemicals and caused damage to a vegetable garden of Grab 'n Grows manager, Don Liepold. Subsequently “I have been testing and detecting herbicide residues and thus rejecting cow manure, horse manure, turkey mulch, rice hulls, mushroom compost and yard trimmings,” says Grab n’ Grow manager Don Liepold. “I spent $20,000 in lab fees in 2008, and am on the same track for 2009,” he says.”
The Mother Earth News article continues “It is extremely difficult to keep contaminated materials out of commercial compost. “One load of contaminated grass clippings can ruin a batch of compost,” says Eric Philip of Anatek Labs in Moscow, Idaho. Philip has seen so many positive tests for clopyralid residues in compost that he would not use untested compost in his own garden.
“When folks have plants die in their home gardens, their first assumption is that they did something wrong,” Philip says. But with pyralid-laced commercial compost becoming more common, contaminated soil amendments are often to blame.
The source of pyralid pollution can be impossible to trace. For example, a horse stable may use hay brought in from a neighboring state, without knowing that it is laced with pyralid herbicides. If the horse’s manure or stable litter ends up in a garden, disaster is ready to strike. It’s better to be safe than sorry. Liepold stopped making one of Grab n’ Grow’s most popular products, Mango Mulch, for more than a year because he could not find an uncontaminated manure supply. Now he’s getting it from two local organic dairies.”
Mother Earth News first sounded the alarm on “killer compost” in 2008, and has continued to report as new information comes to light. In 2011, Dupont's Imprelis, an herbicide praised for being a “green alternative” because of its long residual, made headlines as it killed trees and shrubs in numerous states from New England across the Midwest into the northern Plains States. Currently, the EPA Stop Sale Order on Imprelis, but not on the other products by Dow AgroScience and Dupont.
Dupont did notice that Imprelis could create killer compost. From Page 7 of the 9 page label on Dupont's Imprelis: “Do not use grass clippings from treated areas for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/property managers/residents to not use grass clippings from treated turf for mulch or compost.”
It is well known that the “label is the law”. How many people do you imagine read the entire label when purchasing herbicides? Although Imprelis was sold only to licensed applicators, how many of them read the label or warned home or corporate owner/managers when they applied Imprelis of the long term effects regarding compost? In areas where community composting is practiced, it is easy to see how contamination of these resources can occur.
North Carolina University Cooperative Extension issued an excellent bulletin entitled “Herbicide Carryover in Hay, Manure, Compost and Grass clippings warning “farmers and home gardeners of reported damage to vegetable and flower crops after applying horse or livestock manure, compost, hay or grass clippings to the soil,” (http://www.ces.ncsu.edu/fletcher/programs/ncorganic/special-pubs/herbicide_carryover.pdf). Although the above mentioned products were licensed for use in agriculture by licensed applicators, Imprelis was licensed for use on residential lawns by licensed applicators.
Just because many of these products were for agricultural use, doesn't mean home gardeners are safe from the herbicides long term effects. The warning for vegetable growers and home gardeners is to be aware of your source for hay, straw, manure or compost from hay, straw or manure. These herbicides can be active up to four years or more. The person you purchase or receive these products from may not even know this class of herbicides have been sprayed on them, or be aware of the longterm effects.
Here is an example of why it is difficult to find out. A friend of yours offers you horse manure that has been composted. You might ask him/her if herbicides were used, with the farmer replying the manure/compost is "safe" because the animal has not been effected. The horse or cattle were fed hay that was sprayed with one of these herbicides (it's reported not to be harmful to animals). The horse eats the hay, and the resulting horse manure contains active residues of the herbicide, even after it composts. You spread the manure in your vegetable garden and your vegetables are stunted and fail to thrive, or die outright.
You might think this couldn't happen to you, but a case very similar to what I described happened to a family member of mine. After he did some research, he went back to the neighbor where he got the manure and found out the man did indeed spray his hay with one of these chemicals.
Unless you are absolutely sure hay or straw does not have a history with these herbicides, I would not use them in compost or on your garden soil or ornamental beds.
The affected composted manure would be safe to spread on your turfgrass. To be safe, I would not compost the grass clippings or use the grass clippings in beds or borders. It would be safe to cut your turf with a mulching mow, returning the clippings to the soil if you had already used contaminated compost there. I'm unsure of the effects of these chemicals on trees (except for Imprelis). The North Carolina bulletin goes on to describe how to do tests to determine whether the compost or hay/straw contains residues of one of these herbicides.
The latest warning has come from Mother Earth News, published in the February/March 2013 issue. They noted that livestock feeds now contain the contaminated chemicals and are passed through the animal into the manure in this manner. Because of the growing contamination problem, Mother Earth News advises gardeners that “the time has come for the public to stop buying compost or manure products unless they come from suppliers that are able to afford testing and can screen feedstocks for herbicide residues.”
Once again, the buyer needs to be very aware.
Read More: a FAQ sheet from the US Composting Council on contaminated compost: http://compostingcouncil.org/persistent-herbicide-faq/
The simplest form of composting is covering material with a layer of soil. Organic materials can be composted simply by layering in a heap, without the aid of a structure. If using a structure, the size should be no more than 3 feet tall, but can be any length and width -- whatever works well for you to turn the pile.
I have two wire compost bins I bought after attending a local composting seminar. These wire cages came with a center wire "chimney" to allow for aeration through the center of the pile. Compost bins can take a number of forms, both round or rectangular and box-like, from chicken wire built around fence posts, wood pallets placed upright to form a box, concrete or cement blocks, to purchased composting devices, including barrel composters built with easy hand turning.
Pit composting is similar, only below ground. The sides of the pit could be lined with wood or other supporting material, but in our clay and caliche soil, the soil is firm enough to make this step unnecessary. Usually the pit is not deeper than 2 feet, and about 3 feet wide, and again of any length. Turning the pile is much more difficult and because pit compost piles are usually not turned, they become anaerobic (unless aerated in some manner) and take longer.
Organic materials will compost in black plastic bags that hold 30-40 gallons of material and of sufficient thickness to hold the load (at least 3 ml.). Fill the bag with both brown and green material, a few handfuls of good garden soil or your last batch of compost and slightly moisten contents. One source recommends adding about 1/4 cup of hydrated lime, used to counteract the acidity produced from the anaerobic conditions inside the bag. Set in a sunny spot and wait 6 months. Turning is not necessary. Storing in a shed or garage over winter will hasten the process.
Recommendations of the ratio of carbon to nitrogen vary with the source of information. A good mix of material can be anywhere from 75-80% dry or brown vegetative matter (carbon) and 20- 25% green plant (nitrogen) material or animal manure to a 50/50 blend, lightly moistened. If just using green and brown plant material, add soil and/or manure and lightly moisten as you layer the green and brown material.
Few sources recommend adding raw manures to home compost piles lately, due to the risk of E. coli bacteria and antibiotics and other drugs given to animals. For that same reason, human and pet feces should not be added because of any possible disease pathogens that may not be killed during the composting process.
The carbon to nitrogen ration needs to be in the 25:0 to 30:1 range for an effective compost pile. With too much carbon material, nitrogen is too quickly used, slowing the process. With too much nitrogen, carbon is vented due to microorganisms using it quickly. Wood, woodchips and sawdust have quite high ratios and should be used sparingly, if at all in a normal compost pile.
Carbon/nitrogen ratios of some materails are:
- Wood and wood chips 700:1
- Sawdust 500:1
- Paper 170:1
- Tree leaves 80:1 to 40:1
- Straw 80:1
- Cornstalks 60:1
- Fruit wastes 30:1
- Rotted manure 20:1
- Grass clippings 19:1
- Food wastes 15:1
- Alfalfa hay 12:1
The American Horticultural Society recommends several different formulas of brown and green material for making compost (AHS Resource Bulletin, Compost, Black Gold, adapted with permission from Backyard Composting -- Your Complete Guide to Recycling Yard Clippings):
- 3 parts dry leaves (carbon)
- 3 parts fresh grass clippings (nitrogen)
- 6 parts dry leaves (carbon)
- 3 parts kitchen scraps (nitrogen)
- 3 parts fresh grass clippings (nitrogen)
- 2 parts dry leaves (carbon)
- 2 parts straw or wood shavings (carbon)
- 1 part manure (nitrogen)
- 1 part fresh grass clippings (nitrogen)
- 1 part fresh garden weeds/harvested plants (nitrogen)
- 1 part kitchen food scraps (nitrogen)
- 3 parts dry leaves (carbon)
- 1 part fresh garden weeds/harvested plants (nitrogen)
- 1 part fresh grass clippings (nitrogen)
- 1 part kitchen food scraps (nitrogen)
Be sure to moisten the pile but do not soak it. The microbes need water to decompose the material.
As soil macro and microbial life (primarily bacteria and fungi) break down the material, the pile heats up. A well composed pile will heat up to 135 degrees within 24 -- 72 hours, and up to 150 degrees within 3 days at the center. If the pile does not heat up, turn the pile (be sure the pile was moistened) to add oxygen. If the pile still doesn't heat up, add more green material (nitrogen).
A compost pile temperature of 140 degrees to 150 degrees should be maintained for several days to kill pathogenic microbes. Weed seeds are killed at 150 degrees. Temperatures higher than 155 degrees burn off carbon. If this occurs, turn the pile (turning helps heating and cooling of the pile). Turning the pile also insures all the material will be composted. If turning doesn't cool the pile down, add water, or more brown (carbon) material.
After this initial heating up phase, the temperature of the pile should remain around 104 degrees to 131 degrees. The pile should be teaming with not only microbes (bacterial, fungi, actinomycetes, protozoas, nematodes, springtails,), but macropods: centipedes, ants, snails, slugs, mites, spiders, rove beetles and sow bugs, among others. It takes a grand cast of characters to break down cellulose, lignin, chitin and protein. Don't be surprised to find all manner of "bugs" in the pile. This is not only normal but necessary.
If you've constructed and turned your pile well, you should be delighted to find that beautiful, rich, earthy smelling chocolate brown compost in 2 to 3 weeks. (Teaming With Microbes, A Gardener's Guide to the Soil Food Web, see resources below.) I've never made compost that fast, expect 6 to eight weeks.
Recap of Compost Tips
- The compost pile can be in sun or shade.
- Air and water is necessary for the composting process.
- Carbon/Nitrogen ratio should be 25:1 to 30:1.
- It is not necessary to add nitrogen fertilizer or other commercial starters to the compost pile.
- Inoculation with soil or compost that contain microbes is helpful.
- The temperature must reach 150 degrees to kill weed seeds and most pathogens.
- If you compost materials using the cooler, slower method, do not put weeds or manures containing weed seeds in your compost pile.
- Turning the pile aerates the pile, cools it and helps the pile to heat up. Turning the pile speeds up the process for a quicker end product.
- We don't have to worry about covering it in our climate. But if we ever experience an extended rainy period where the compost pile is in danger of becoming saturated, then cover before it reaches this point.
- During Panhandle summers, add water when turning the pile; compost piles in our climate dry out.
- Never compost plants or manures exposed to persistant herbicides
Composting Sources for Additional Information
There are many excellent sources for composting information. An excellent book on the explanation of and the benefit of the soil food web is Teaming with Microbes, A Gardener's Guide to the Soil Food Web, by Jeff Lowenfels and Wayne Lewis, Timber Press, 2006. This book also offers guidance on tailoring your compost for particular plant types.
Most books on organic gardening and composting will cover the subject of composting quite well. Information was also taken from The Rodale Guide to Composting, by Jerry Minnich and Marjorie Hunt, 1979, Rodale Press.
Each of these links provides extensive information on composting. Please look at several of them. These are just a few of the many, many website with composting information.
- Texas Cooperative Extension's Don't Bag it Composting Program
- Cornell University Composting
- Compost Guide
- EPA Compost Information
- Natural Resources Conservation Service Composting Info
- City of Austin, TX Composting
- Soil Food Web/Compost Food Web