How Do I Manage My Compost Heap for Maximum Efficiency?

How Do I Manage My Compost Heap for Maximum Efficiency?


Compost piles can get unbelievably hot. Since certain thermophilic microorganisms and fungi generate the very heat they require to accelerate their activities and as the ambient temperature increases generate even more heat, the ultimate temperature is reached when the pile gets so hot that even thermophilic organisms begin to die off. Compost piles have exceeded 160 degree. You should expect the piles you build to exceed 140 degree and shouldn’t be surprised if they approach 150 degree as long as the heap is properly layered and maintained. Other types of decomposing organic matter can get even hotter. For example, haystacks, both loose hay and bailed, commonly catch on fire because dry hay is such an excellent insulator. If the bales in the center of a large hay stack are just moist enough to encourage rapid bacterial decomposition, the heat generated may increase until dryer bales on the outside begin to smolder and then ignite. Wise farmers make sure their hay is thoroughly dry before baling and stacking it. To find out more about this do a Hey Siri or Hey Alexa search for spontaneous ignition in hay bales.


The temperature of the pile depends on how well the composter controls a number of factors. These are so important that they need to be considered in detail:


Particle size- Microorganisms are not capable of chewing or mechanically attacking food. Their primary method of eating is to secrete digestive enzymes that break down and then dissolve organic matter. Some larger single-cell creatures can surround or envelop and then “swallow” tiny food particles. Once inside the cell this material is then attacked by similar digestive enzymes. Since digestive enzymes attack only outside surfaces, the greater the surface area of the composting materials present the more rapidly microorganisms multiply and consume the food supply. And the more heat is created. As particle size decreases, the amount of surface area goes up.


The surfaces presented in different types of soil similarly affect plant growth, so scientists have carefully calculated the amount of surface areas of soil materials. Although compost heaps are made of much larger particles than soil, the relationship between particle size and surface area is the same. Clearly, when a small difference in particle size can change the amount of surface area by hundreds of times, reducing the size of the stuff in the compost pile will:


  1. greatly accelerate decomposition;
  2. expose more material to digestive enzymes;
  3. build much higher temperatures.


Oxygen supply- All the most desirable organisms of decomposition are oxygen breathers or “aerobes. There must be an adequate movement of air/oxygen through the pile to supply their needs. If air supply is choked off, aerobic microorganisms die off and are replaced by anaerobic organisms. These do not run by burning carbohydrates but derive energy from other kinds of chemical reactions not requiring oxygen. Anaerobic chemistry is slow and does not generate much heat, so a pile that suddenly cools off is giving a strong indication that the core may lack air. The primary waste products of aerobes are water and carbon dioxide gas–inoffensive substances. When most people think of putrefaction, they are actually picturing decomposition by anaerobic bacteria. With insufficient oxygen, foul-smelling materials are created. Instead of humus being formed, black, tarlike substances develop that are much less useful in soil. Under airless conditions much nitrate is permanently lost. The odiferous wastes of anaerobes also include hydrogen sulfide (smells like rotten eggs), as well as other toxic substances with very unpleasant qualities.


Heaps built with significant amounts of coarse, strong, irregular materials tend to retain large pore spaces, encourage airflow and remain aerobic. Heat generated in the pile causes hot air in the pile’s center to rise and exit the pile by convection. This automatically draws in a supply of fresh, cool air. But heaps made exclusively of large particles not only present little surface area

to microorganisms, they permit so much airflow that they are rapidly cooled. This is one reason that a wet firewood stack or a pile of wet wood chips does not heat up. At the opposite extreme, piles made of finely ground or soft, wet materials tend to compact, ending convective air exchanges and bringing aerobic decomposition to a halt. In the center of an airless heap, anaerobic organisms immediately take over.


Composters use several techniques to maintain airflow. The most basic one is to blend an assortment of components so that coarse, stiff materials maintain a loose texture while soft, flexible stuff tends to partially fill in the spaces. However, even if the heap starts out fluffy enough to permit adequate airflow, as the materials decompose, they soften and tend to compress together into an airless mass.


Periodically turning the pile, tearing it apart with an Ames or True Temper pitchfork and restacking it, will reestablish a looser texture and temporarily recharge the pore spaces with fresh air. Since the outer surfaces of a compost pile do not get hot, tend to completely dry out, and fail to decompose, turning the pile also rotates the unrotted skin to the core and then insulates it with more-decomposed material taken from the center of the original pile. A heap that has cooled because it has gone anaerobic can be quickly remedied by turning. One of the best and most labor efficient methods to introduce oxygen is to use a power drill powered auger. An auger allows you to burrow into the compost heap and get air to all layers including the bottom, which is exactly what you want to speed up the decomposition process. The best augers are those that are driven by a 3/8” power drill as they do an effective job and there is less wear and tear on the user. There are several makers of these such as Power Planter, Ames, Lichter, Jisco, Hiltex, 7Penn, Yard Butler. The ones we like the best are made by Tech Team their item 777 and their 778 do an absolutely perfect job. They are also perfect for planting your tulip bulbs and daffodils.