Compostable Greenhouse Growing Bag Trials Encouraging

Convex Plastics, September 12th, 2011

Convex Plastics is one step closer to developing a functional compostable growing bag that will eliminate the mountain of landfill waste created by commercial greenhouse tomato growing.

A 15-month cherry tomato growing trial that Convex was involved in last year has enabled the Hamilton company to develop a customised compostable film that is purpose designed to function well in a greenhouse.

A new ten-bag growing trial got underway in July to check the new film will perform as expected and stand up well to the humid greenhouse conditions and continuous exposure to UV sunlight.

Convex Technical Manager, Andrew Sheerin says the data gathered in last year’s growing trial enabled his team to reformulate the compostable EcoFuse hybrid film used in the last trial to make it more fit for purpose.

As part of the trial, new tomato vines are planted in compostable EcoFuse growing bags and filled with imported coco fibre. Just prior to the seedlings being planted, about 10 litres of water is poured into the growing bags to inflate the coco fibre to approximately five times its original size. The original EcoFuse blend of 45% Poly Lactic acid (PLA) derived from renewable corn and 55% biodegradable Polyester (made from non-renewable petrochemicals) did not cope well with the outwards pressure generated by this process, and some splitting issues occurred.

Andrew says, “Our primary aim is to develop a fully compostable growing bag that will not split or prematurely breakdown. The first trial identified what we needed to do to boost the longevity of the growing bags and make them more robust.”

This has resulted in the development of a new EcoFuse blend that includes a lower ratio of PLA, while still being fully compostable.

While Convex would ideally like to make the growing bags 100% renewable, Andrew says the technology currently available doesn’t allow them to achieve that. The bags need to be robust enough so they can be lifted out of the glasshouse by hand at the end of the growing season and stacked on pallets outside in one piece. By the end of the last growing trial the bags made with the original blend of EcoFuse were too brittle for this to occur and they were splitting.

Andrew says, “The primary driver of this project is to make the growing bags compostable so we can eliminate the mountain of landfill waste that the standard plastic growing bags are producing, and we are well on track to achieving that. Disposing of the current polyethylene growing bags is both tricky and time consuming as they have to be separated from the organic waste. Making the bags compostable will save a lot of time and significantly reduce the landfill waste generated by this type of greenhouse growing by enabling the discarded growing bags to be composted with the organic tomato and growing media waste.”

Andrew says the initial checks of the new growing bags have been quite encouraging.

“The new growing bags already appear to be more robust than those made with the previous blend and early indications suggest that we have solved the splitting issue.”