Guernsey Waste improves the quality of its free garden compost

Thursday, 11 June 2026 11:28

By Euan Mahy

The 'windrow' method ensures the temperature of garden waste is constantly monitored to provide optimum conditions.

Keen gardeners in Guernsey have long been part of the virtuous circle where they take clippings to the green waste site and then collect the resulting compost for free.

Guernsey Waste says the quality of compost is better and more consistent having adopted the 'windrow' method.

Guernsey Waste's Douglas Button says a digger makes separate piles of garden clippings and their internal temperature is closely monitored:

"The piles are two metres wide and two metres high, or vary, depending on the amount of material we have for consistent rows that run lengthways.

"Once it's in rows we just let it decompose and put in temperature gauges to make sure that it gets to a certain temperature, then we have to turn it."

Douglas Button says the inside temperature can reach 70°C, which promotes faster composting and sanitises the material:

"Heat probes monitor the exact temperature that the microbial activity is causing.

"When it gets to about 70° we then turn it, which is the optimum time to turn it, because you’re getting a lot of breakdown of material, but it’s not exceeding the temperature where it goes anaerobic."

He says it is this scientific approach to composting, including adding water in the summer, that produces a better grade of compost.

The compost is then finely graded to remove contaminants.

"By screening down to 10 millimetres we take out anything that may not have decomposed within that time and that goes back into another windrow, to be decomposed further."