Greenhouse Canada

Fall’s a good time to start a healthy compost pile

December 2, 2008  By Lee Reich The Associated Press

Dec. 2, 2008 – This time of year, autumn leaves and garden debris, in addition to the usual grass clippings and kitchen trimmings, quickly fill compost bins. Now's the perfect time to encourage your customers to erect their own compost bin.

Taking your compost pile's temperature is one way to tell how it's doing.

A healthy compost pile often has a passing, healthy "fever" that may be as high as 65 C. This temperature, which a compost pile might maintain for a few days, is enough to cook to death virtually all pathogens, insects and weed seeds.



An abundance of compost materials makes autumn a good time to assemble a large pile all at once, and large, quickly assembled piles are the ones most likely to get steaming. Heat dissipates too easily from a small pile – one less than one metre on a side – and heat is lost as rapidly as it is produced from a pile built very slowly.

This time of year, autumn leaves and garden debris, in addition to the usual grass clippings and kitchen trimmings, quickly fill compost bins.

The steam you often see billowing out of compost piles comes from the combined body heat of bacteria, earthworms, fungi and other organisms working away at digesting raw materials. All these
organisms are happiest if provided adequate food, water and oxygen.

By adding a wide variety of materials, you offer a smorgasbord of nutrients, and the different textures allow for good aeration. For instance, old corn stalks or straw fluff up grass clippings or maple leaves, either of which packs down into a sodden mass when used alone.


The most important thing you can do for your compost pile is to enclose it in some kind of bin. An enclosed pile is easier to build and, depending on the material, will retain heat and moisture better than an open pile, which can too easily look like a pile of garbage.

Once materials are assembled, composting organisms get right to work in a wonderfully orchestrated sequence of activity. First come those organisms that thrive at lower temperatures, the so-called psychrophiles, which work happiest from below freezing up to about 21 C.

Once temperatures warm a bit, the next group, the mesophiles, get to work, and continue to do so up to about 37 C.

As internal temperatures rise, the group of organisms called thermophiles start to multiply. They work above even 71 C.

After a few days at high temperatures, thermophiles have finished their food and are exhausted, so temperatures begin to drop. Mesophiles and psychrophiles waiting at the cooler edges of the pile multiply and move in, and they, along with earthworms and other creatures, finish the work. The temperature drop takes a few weeks in summer, but is hurried along in autumn's coolness.


There's no need to fret over the temperature of a compost pile. Sliding the long probe of a compost thermometer into the innards of a compost pile is just a way to see what the "herd" within is doing. Are they working fast, so decomposition will be well on its way before colder weather temporarily slows or stops activity? If the herd is sluggish, perhaps the pile needs moisture or more nitrogen – manure or a sprinkling of fertilizer – to get cranking.


Whether the herd works quickly or slowly, however, any pile of organic materials eventually turns to compost. So don't worry if your pile never gets a fever. At lower temperatures, the process is merely slower.

It is a combination of temperature and time that does in bad guys, such as diseased plants, within the pile. If an hour at 60 C kills a pathogen, that pathogen might still die at 48 C in 24 hours, even at a balmy 37 C in a week.

Whether you compost fast or slow, the material is ready to use once it is brown, with the original materials no longer recognizable, and when it has a nice woodsy smell. The pile also will have cooled to surrounding temperatures.

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