Research

Paul Alexander

There is a wealth of information out there for home composters but there appears to be a lack of scientific studies. This research aims to improve gardeners' composting by improving our scientific understanding.

The research initially examined the effects of different bin types and the effects of turning (or not) upon the temperature, quality and volume of compost produced. The experiment used three types of bin:

• wooden (volume 1m 3),
• black plastic - available from local councils (volume 0.3m 3),
• open heaps (volume 0.3m 3 ).

Garden waste from a large RHS Garden Wisley compost heap was used to fill the test bins and allowed measurement of temperature in a large heap (greater than 30m 3 ) for comparison. All the heaps were turned once a month from November to the following October.

The amateur bins composted at about 5 °C above air temperature for the course of the experiment (In comparison, the larger garden heap exceeded 50 °C for most of the year. The wooden bins composted significantly warmer than the plastic and open heaps for most of the experiment but not at high enough temperatures to suppress pathogens or weeds. Interestingly, the plastic bins composted significantly warmer than open heaps. This was possibly a positive effect of the container. Turning only really stimulated increases in temperature in the larger wooden bins.

When the bins were broken down, all bin types, irrespective of turning, yielded around 1/3 less compost than the starting volume, of which 80% was determined as being made up of fine (less than 10mm) particles.

Weed germination assessments with the 'fine fraction' suggested only the open heap compost had significant weed populations.

Seed germination tests with lettuce and tomato suggested that planting in the composts delayed germination, due to high nutrient content, except in the open heap compost where analysis showed nutrients had been leached out.

Further work to examine minimum heap size for elevated temperatures, specific compost mixes and developing our understanding of compost quality would be of great interest.

For the article on home composting in the RHS Science Departments Report 2004, click here.

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