A common misunderstanding about compost piles is that they must be hot to be successful. This just isn't true. If you have good aeration and moisture, and the proper ingredient mix, your pile will decompose just fine year-round at normal Scottish temperatures.  It will slow down considerably when temperatures drop below freezing, but start up again as the day warms up.

Hotter piles will decompose faster, however.

... Generally speaking, a hotter pile means more microbes or conditions that allow the microbes to have faster metabolisms, and therefore a faster composting process. If you'd like to keep your pile as warm as possible, consider the following:

For a pile to get hot and stay hot for a long period of time, the typical minimum size is one cubic meter (i.e., a cube that is one meter -- about three feet -- on each side). A pile this size has enough mass to support those billions of heat-generating microbes, yet is also large enough that the centre of the pile is well-insulated by the material surrounding it. Smaller piles just cannot insulate themselves well enough to remain hot for long, if at all.

To get it started:

1. Gather both "green" and "brown" ingredients, enough to make a compost pile measuring at least 1 metre (3 feet) in each direction (high, wide and long).  In other words, fill your bin completely. (NB: One of the things we want to learn in Dunblane is how well the compost heats for those of you with the smaller bins that are less than 1 metre square.  Please call or write for advice if you have difficulty.  You may be better advised to try ‘Cold Composting’ or ‘High Fibre Composting’ detailed below).

2. Chop or shred into small pieces as much of the material as possible. Smaller materials make a better home for decomposer organisms, with more surface area for them to work on. The finer the pieces, the faster your compost will be finished.   Garden shears or hedge trimmers will work, even if they are tedious with large amounts. Dry materials like leaves can be run through a shredder (if available), or a lawn mower can be run over them.

3. Layer 15 cm (6 inches) of well-watered "browns" and 15 cm of "greens," then mix the first two layers together.    

4. Alternate and mix layers of each type of material, adding water as needed, until the box is full. Adding the material in layers simply helps you judge the right proportions of "brown" and "green." But everything should then be thoroughly combined to compost efficiently.     

5. Close the lid to protect it from heavy rain, and wait. The compost should begin to heat up within hours. 

To witness decomposition in action, you can stick a metal rod into the centre of the pile for a few minutes, then check if it has warmed up. Compost thermometers are available at garden centres, or you can even mount a meat thermometer at the end of a stick if you want precise temperature readings.  Vapour emerging from between the slats, and a fine grey fungus just under the surface, are other good signs of an active hot compost.  

What if it doesn't heat up? 

When a ‘hot’ compost pile won't heat up, the problem is almost certainly one of three things:

a) the pile is too small

b) it's too dry

c) it needs more "greens" or, especially in cold weather, a "starter" to give it more nitrogen.

The Hot Composting Timetable

The temperature of the pile should rise steadily, peaking between 50 and 65 degrees C (120-150 F), 24 hours to one week later. When the temperature begins to drop, the compost is ready for turning. Break up any clumps of material, and move the outside parts to the base and centre. If the pile is too dry, this is the time to wet it. Close the lid again, and wait. The temperature should peak again in about a week, in a pile made of well-shredded materials. (Remember, the smaller the pieces, the faster the compost.)

As soon as it begins to cool, turn the pile once more. In another week or two, the compost should be finished; that is, dark and crumbly, fresh-smelling, with very little of the original material identifiable. When compost is ready for use, the temperature of the pile won't rise above 43 degrees C (110 F) no matter how often you turn it.

Key Points to Remember      

· Use equal amounts of "greens" and "browns."     

· Mix together a variety of ingredients.      

· Shred or chop all ingredients, if possible.     

· Build the pile large enough to retain heat.     

· Turn or aerate the heap regularly to let in air.