Clean Calgary Association

Frequently Asked Composting Questions

These are the most common questions asked by Calgarians concerning composting. If you require more information please contact us and we would be more than happy to assist you.

Why Should I Compost?

Organic materials are a valuable resource in the garden either as a compost or a mulch. Mulches and compost improve soil texture and plant health, prevent erosion and hold moisture and nutrients. Their production and use in this way can enable a typical household to reduce the amount of garbage they send to the landfill by one third to one half. Finished compost made from household wastes is free to the householder. Waste diverted to composting or mulching saves the City of Calgary (and ultimately the taxpayer) the cost of collecting it and disposing of it. Diminishing landfill space is therefore also conserved. Organic materials placed in a landfill decompose only under anaerobic conditions. One of the byproducts of anaerobic decomposition is methane gas, which is odorous, explosive and contributes to the greenhouse effect. Landfill leachate is also a product of concern.

Do I Need A Bin or Container To Compost?

No. The composting process is a natural one and will take place in an open pile as well as a compost bin. Bins or composters help keep a compost pile neat, provide some weather protection, and will keep out rodents and pests. They are recommended for a close urban environment. Composters can be made or purchased. Clean Calgary provides plans for a number of standard composter designs for those that would prefer to build their own. These may be followed or adapted to suit particular needs and materials.

What Composter Should I Build or Buy?

The correct decision as to what composter to build or buy will depend upon a careful consideration of a number of factors such as the amount of material to be composted, the amount of room available, the cost, the appearance of the composter and how much time and labour can be devoted to operating it. If the decision is made to compost, IT IS MUCH MORE IMPORTANT THAT IT BE DONE CORRECTLY RATHER THAN WHAT COMPOSTER IS USED. In process terms, most of the home composters available commercially in Calgary work. Any shortcomings or faults attributable to any particular model can be overcome through an understanding and intelligent application of the principles involved in home composting.

If the process variables are factored out, the choice will depend upon cost, durability, appearance and size. Home composters can be made of various combinations of wood, plastic, and metal. In general, recycled plastic costs more than virgin wood which, in turn, costs more than salvaged wood. Metal and virgin plastic is comparable in cost to virgin wood.

How Big Should the Composter Be?

This will depend on the amount of material to be processed and the amount of room available to site a composter. With an average City lot, most of which is given over to turf, one to two holding type bins, each capable of enclosing a cubic metre in volume, should be adequate. Larger yards may require a turning type composting system. There is a very significant volume shrinkage to waste materials as they are composted. Finished compost will only occupy from 10% to 40% of the original waste volume.

There are a number of methods that can be utilized to take advantage of the volume shrinkage inherent in aerobic composting and maximize the volume available in a small composter unit. Grass clippings can be left on the lawn every few cuttings or used as a mulch, for example. If the composter is filled during periods of fast grass growth, some of the overflow clippings can be stored in sealed plastic bags and added to the unit after the initial volume shrinkage occurs. The continual feeding of the nitrogen rich clippings at small intervals will also help maintain thermophilic conditions in the pile.

Where Should I Place the Composter?

A composter should be placed on a well drained site to prevent the saturation of the material in the bottom of the unit and the creation of anaerobic conditions. Siting the composter so that it receives some direct sunlight will aid in process heat gain and retention. At the same time, solar heat will cause the pile to dry out faster, which may or may not be desirable.

In an urban setting, a composter should be sited in a yard so that its presence and operation is not a nuisance to the neighbours.

How Long Does It Take To Produce Finished Compost?

Under typical Calgary conditions, with a moderate amount of care and attention, it will take a growing season to produce a stable, humus like "finished" compost. This also assumes that large amounts of high carbon materials that are slow to break down (such as sawdust or wood bark) are not being composted. There is a danger of compost containing the latter materials causing a nitrogen immobilization or deficiency in the soil as it is incorporated into it. Bacteria are more efficient at using nitrogen than plants. They will therefore "rob" plant life of the soil nitrogen in order to further break down the high carbon materials.

Following the University of California Method, compost that is semi-stabilized can be produced in between two to four weeks during an Calgary summer. Partial sterilization of pathogens and weed seeds will have occurred and the readily decomposable materials will have been broken down. The origin ofmanv wastes will still be discernible however. They may still be discernible for up to a year following soil incorporation at this stage. Using less labour intensive methods, finished compost may take up to two years to be produced.

How Do You Tell When Compost Is Finished?

The composting literature proposes a number of methods to tell when compost is fully stabilized or "finished". These include C:N ratios, plant bioassays, degree of self-heating capability and spectroscopic techniques. Unfortunately, these methods are unavailable to the average householder.

Odour and visual appearance are, by themselves, not reliable indicators of compost maturity. An earthy odour is only indicative of the presence of actinomycetes. The first notice of this smell, at least, is therefore more indicative of there still being unstable organic matter present. Similarly, a dark coloured composting mixture may still have too high a C:N ratio that could lead to nitrogen immobilization.

For home composting purposes, compost may be assumed to be fully "finished" when a number of indicators coincide. Stable compost has been described as dark brown or greyish black in colour, with a sweet, earthy smell and a loose, crumbly texture that feels and looks like topsoil.

Can I Compost in Winter?

Bacterial activity slows down drastically under typical Calgary winter conditions. While thermophilic conditions can be maintained in large scale windrow or aerated static pile composting operations, it is impractical to construct these same size piles in home composting. Some heat may be generated in a home composting operation as quantities of fresh household waste are added to the pile. Any rise in pile temperature is very short lived however, and conditions will soon revert to ambient. Insulating a pile with large amounts of dry cover materials such as straw or hay will retard the loss of interior heat as will ensuring a supply of easily decomposable high nitrogen feedstock.

Materials may continue to be added to the pile over the winter. As the pile is in an essentially dormant state, there will be very little volume reduction associated with the new materials. If the composter fills up, kitchen wastes may be stored outside in sealed containers or plastic bags and left to freeze. Odour is not a problem with these materials in a frozen state. In the spring, the wastes may undergo a number of freeze thaw cycles that will aid in the breakdown of their cell structure once they are placed in the compost pile. A Compost pile will become active again as ambient temperatures warm up. The kitchen wastes that were stared aver the winter and added to the pile should be mixed with drier materials such as leaves or straw to absorb the excess water generated from freezing.

What Can I Do With My Finished Compost? Will I Have too Much?

There are a variety of uses for finished compost. Its most beneficial use is as as soil conditioner incorporated into an ornamental or vegetable garden or spread on a lawn as a top dressing. Though low in nutrient value compared to chemical fertilizers, compost nutrients are in a slow release form due to their chemical bonding with organic matter. Mixed with garden soil, it will help to improve its water retention properties, its workability and pH buffering capacity. Materials in the compost that have not really broken down, such as woody twigs, may be screened out and put back into the compost pile.

Finished compost can also be used as a potting soil amendment for house plants. The caution here is that it should be completely sterilized first through heat treatment in order not to infect house plants with insects that migrate into the compost pile during its later cooler stages. These insects are useful in the further breakdown of organic material in a compost pile, but are a nuisance around house plants.

As previously stated, the volume of finished compost produced is very small in comparison to the volume of the original waste materials. It can be used virtually any place in the garden. The more usual problem with experienced home composters is an insufficient quantity of the material rather than an oversupply.

How Do I Prevent or Solve an Odour Problem?

Most odour problems are caused by the composting mixture being too wet, anaerobic conditions occurring, or a nutrient imbalance in favour of too great a quantity of easily decomposable nitrogen materials. The first two conditions are related in that the majority of oxygen transfer only occurs in the void spaces not occupied by water.

The proper preventative measures to take to prevent odours are to ensure a proper starting C:N ratio (25:1 to 30:1), a proper moisture content (like a damp sponge) and sufficient aeration through turning. Microbiological reaction rates will increase during periods of warm weather with an attendant increase in the rate at which atmospheric oxygen is used up. Consequently, the pile should also be turned or agitated more at these times.

Measures that may be taken for offensive odours resulting from the composting mixture being too wet include mixing in drier materials and turning it more ~frequently to provide more air exposure. Turning and agitation will also induce more aeration, as will the addition of materials with greater structural strength such as twigs or straw. High carbon materials added to the pile such as dry leaves, small quantities of sawdust and shredded paper will help to offset an excess of high nitrogen materials. In extreme cases, the entire pile can be broken down and reconstructed with other material amendments as required. Dry topsoil sprinkled on top of a compost pile will also act as an absorbent for offensive odours.

Another possible reason for odours from a home compost pile is the addition of improper materials such as meat, grease and dairy products. In addition to being slow to break down, they also quickly turn rancid. The solution in this case is to not compost these materials or to remove them from the pile if already present.

Are Pets, Rodents or Other Animals Attracted to a Compost Pile?

Animals are typically attracted to a compost pile for two reasons: food and warmth. Cats, dogs and rodents will not be attracted if meat, bones, fish and other food products eaten by these animals are not placed in the compost pile. Maintaining a very hot compost pile will also aid in keeping these animals away.

In the winter, small rodents, such as mice and voles, will be attracted by the insulating and easy burrowing qualities afforded by an open compost pile. The best measure to use to prevent this is to enclose the entire pile within a "pest-proof' container or bin. This should be equipped with a tight fitting lid, a closed perforated or wire mesh bottom, and air holes less than an inch in diameter. Spaces that might provide entrance into the pile should be blocked off with sturdy half inch (or smaller) wire mesh.

How Do I Prevent Attracting Flies and Other Insects?

Flying insects are attracted to kitchen wastes with a high sugar content such as fruit and vegetable peelings. These materials should be immediately buried and covered inside a compost pile. The maintenance of a hot compost pile will also destroy insects at the larval stage.

Can I Compost Weeds or Diseased Plants?

Evidence from large scale composting operations indicate that both weeds and diseased plants will be destroyed through the high process temperatures achieved. This is not the case in a home composting operation.

Broad leaf weeds that have not gone to seed may be safely composted at home. Care must be taken with those that have. While the general rule of thumb is that weed seeds will not remain viable if the combination of moisture content and temperature in degrees Fahrenheit is greater than 100, there is no guarantee in a home compost operation that this will occur uniformly or at the specific point in the pile where the weed seeds are placed.

The lower, below ground, portion of weeds that spread by rhizomes (nunners) such as crab grass should not be placed into a compost pile fresh, even if shredded. They will be acceptable if they are first dried out thoroughly after being spread out on pavement.

Finally, diseased plants should not be added to a home compost pile because of the possibility of the disease organisms surviving the composting process and propagating further as the ~finished material is used throughout the garden.

Can I Compost Plant Material Treated with Herbicides & Pesticides?

Herbicides and pesticides intended for residential use generally have short residence times. Broad leaf herbicides do not affect grass plants and the residues are either washed away by rain or watering or are oxidized or broken down by ultraviolet light. Residential pesticides residues also have short residence times and are subject to environmental degradation by air, sunlight and heat.

Documentation in the literature from large scale yard waste composting operations indicate that most herbicide and pesticide residues will be volatilized through the heat of composting. The residual toxicity of any remaining compounds will also be significantly reduced due to them being tightly bound to the organic matter present.

Even given the above, the conservative procedure would be to not compost with herbicide or pesticide treated plant material. This means clippings from the first few lawn cuttings after a herbicide is applies are not placed in the compost pile. It also means that composted pesticide treated materials are not used in areas of the garden used to grow food or are left to cure for a year to allow for environmental degradation of any residual compounds.

Can I Compost Paper?

Small amounts of certain types of paper, such as shredded newsprint pulp, coffee filters and tea bags are acceptable in a compost pile. Paper has no structural strength when wet and will reduce the overall percentage of air voids in the composting mixture. Due to its cellulose content, it also takes longer to break down than other organic materials. Glossy magazines should not be composted because the clay coating on the stock inhibits decomposition and some of the printing inks used are toxic.

Paper stock from newspapers (pulp) and magazines are best dealt with through the recycling depots.

Can I Compost Pet Wastes?

Care must be taken when dealing with pet wastes. Wastes from dogs, cats and other carnivores may contain human pathogens that survive the home composting process. These materials should therefore not be used. Pet wastes from certain herbivores such as rabbits, guinea pigs and hamsters, however, are not pathogenic and may be composted in the usual manner.

Manures from farm animals have often been recommended as natural compost activators. For ease of handling and less odour problems, they should be well rotted prior to use. Manure from horses and other pasturing animals tend to contain a lot of weed seeds.

Do I Need To Use a Commercial Compost Starter or an Accelerator?

No. Commercial compost starters or accelerators sold as such typically contain a source of nitrogen or protein or dehydrated bacteria. No commercial nutrient activator is required if care is taken to ensure that the composting mixture contains the proper C:N ratio. If an additional nitrogen source is required, high nitrogen "green" materials such as grass clippings may be added or a natural activator such as bloodmeal or bonemeal sprinkled in. On a weight basis, the latter are more economical than commercial nutrient starters.

It is also unlikely that any commercial bacterial based activator is any better adapted to decompose the waste materials than those already present. If required, garden topsoil or finished compost may be added to the composting mixture to introduce more of the composting microorganisms to the waste materials.

Depending upon the constituent materials, the pH of finished compost will be close to neutral.

Some yard waste composts will be slightly alkaline, those made from large quantities of acidic materials such as pine needles and oak leaves may be slightly acidic. The large amount of organic matter in finished compost will also give it a significant buffering capacity. Upward adjustment of the pH level through lime addition should not be required.

September 5, 2008

© 2008 Clean Calgary Association.
Site by Shadow Box.