Composting residual wastestreams from glasshouse cultivation

VLACO and the Research Station for Vegetable Production work together on the residual stream of fruit vegetable foliage. In Flanders, this accounts for some 15,000 tons per year. This is a residual stream that is difficult to recycle due to the presence of non-biodegradable auxiliary materials (nylon ropes, clips, brackets, etc.). The use of biobased plastics or other degradable components such as viscose is a step in the right direction. However, compostability remains a challenge. In addition, these foliage residues become available in a short period of time in the fall.

The partners are investigating how this residual stream can be sustainable processed via composting. Initially, they explored how to work out the storage of these harvest residues. By trying to store them over a long period of time, they can be added to compost for longer. For example by ensiling them, or wrapping them in bales.

In addition, the partners will find out how biobased materials break down in the compost process and where improvements can be made. The greenhouse foliage will also be composted in smaller-scale farm composting. The end product of this will be used in the multi-year compost trial that has been running since 2006 at location of the Research Station.

CLOSECYCLE is building on the initial results obtained in Cmartlfe from 2021-2023. For the residual streams released from the different fruiting vegetables, the findings were detailed in interesting fact sheets.

Optimising plant waste flows through storage solutions

Cucumber cultivation illustrates a major logistical challenge: at the end of the growing season, over 90% of the plant material becomes available within a very short time. Currently, only a small portion of this biomass is composted. As greenhouse agriculture transitions toward more circular and sustainable practices, immediate composting of all plant residues is impractical and could create logistical problems.

One of the central questions within the CLOSECYCLE project, conducted at the research station, is whether it is possible to store plant material effectively and initiate composting after storage. If feasible, this would allow the material to be used over a longer period, rather than all at once. Different storage techniques will be explored to support this phased approach to composting.

Pilot study: Silage of cucumber vines

To explore short- to medium-term storage strategies, a pilot trial was launched in June 2025 at the research station, focusing on the preservation of cucumber vines through silage. For this study, bokashi buckets were used to test different combinations of materials:

Control: cucumber vines only
Cucumber vines with 10% and 20% chicory roots added for their high sugar content, which enhances fermentation and lowers pH
Cucumber vines with a silage additive (TMR+) which improves fermentation quality and inhibits mold development

Throughout the trial, internal temperatures are monitored continuously and at the end, parameters such as pH and ammonia levels will be measured to assess preservation quality.

Toward scalable circular solutions

In August, the research entered a new phase with the launch of a large-scale silage trial. Around 2 tons of cucumber plant residues were ensiled to test the method under practical, real-world conditions. The batch was divided into two treatments:

One part was ensiled with the TMR+ additive
The other part was ensiled without any additive

The effectiveness of preservation, ease of handling, and quality of the stored material will be compared across treatments.