Circular Horticulture, Part 2: Pitches

Last week I attended Wageningen Research’s Greenhouse Horticulture business unit’s event on research into circular horticulture for 2025. After the main presentation on the group’s vision and ideas (which you can read about here), there were six short presentations. Three of these were done by students (including me).

There were some very interesting ideas here! Without further ado, let’s go through them.

Jim van Ruijven – Circular Water in Greenhouse Horticulture

Jim van Ruijven is a researcher specialised in the topic of greenhouse water and nutrient management, specifically nutrient emissions. I cited him in my BSc thesis a few times, so it was interesting to see the face behind the name.

Jim’s presentation started with a diagram similar to Alexander Boedijn’s (see the article before this), visualising the water going in and out of greenhouses. 77% of the water used in Dutch greenhouses is rainwater.

The rest comes from wells. As for water leaving the greenhouse, about 4% is lost through leaching. 87% is lost through transpiration. The main problem in this whole balance is that wells are a finite source.

One solution could be to use active condensation, recovering the water lost through transpiration. Unfortunately, this usually doesn’t provide enough water. A better solution would be to use the water from other processes in the neighbourhood (begs the question of where the water in these processes comes from, but anyhow better than directly using well water).

Jim mentioned a few principles worth considering for water management. Quality and quantity are important, but so are timing and buffering. Very often, these are limiting factors. Transport distance is also a limiting factor for water.

Lastly, Jim gave some examples of how adding functions can help greenhouses’ water management become more locally embedded. They can be used for water buffering, flood prevention, or supply – a bit like how electric cars are being used to stabilise the electricity grid, I’d imagine.

Cristiana Necula – Circular Greenhouses: Building an Innovation Hub for High-Tech Horticulture in Romania

Cristiana is a master’s student in plant sciences from Romania who is looking for solutions based on sharing knowledge to speed up the transition towards a circular agri-food industry.

In Romania, tomatoes are mostly grown in open field polytunnels (not everyone is as advanced as the guys at PlantGeek). Annual yield is only 18 kg per square metre, whilst using 400 litres of water per kg of produce. At the same time, Romania is dependent on imports when it comes to vegetables.

Because of this, Cristiana is in a group interested in implementing a circular high-tech greenhouse in Romania, which aims to be economically viable. This project would form the base of an innovation hub for the region where data and knowledge can be shared.

If this all sounds a bit vague, it’s because the idea only just started to come to fruition in December. It will be interesting to see what they come up with later on!

Me – Aquaponics, Mushrooms, Insects: Bringing Ecosystems Indoors

My pitch was an abridged version of my TEDx talk from 2018. It was a conceptual presentation about the benefits of applying the principles of ecosystems to indoor agriculture.

The two main benefits, which you can read about in the linked articles on this blog, are:

I might one day write a post putting all of these ideas into one article.

Bas Hetterscheid – Insects are Closing the Loop

Bas works on post-harvest technologies at Wageningen Food & Biobased Research. His presentation was on the three heroes of circular agriculture: the black soldier fly, the yellow mealworm, and the cricket.

Bas then went on to present insects’ context within ecosystems, similar to my presentation but more specific. The idea is that insects can process waste, producing protein and manure. Interestingly, insects grow best on waste like swill and pig manure. Wow, it’s as if that’s what they had evolved to do within the ecosystem.

The two main takeaways Bas ended with were that people should consider insects when thinking about circularity. In fact, that is what his department is looking for: biowaste from horticulture to test on insects in 2020.

Hessel van der Heide – The Potential of Black Soldier Flies in Integrated Pest Management

Every now and then, there are these presentations about fascinating biological interactions. Hessel’s was one of these.

When growing insects like black soldier fly larvae, a big waste product is the frass. Frass contains insect manure, but also dead larvae shells, which are shed multiple times throughout their life cycle. These shells are mainly made of chitin, which is hard to digest. Even fish spit out these chitin shells when they are fed BSF larvae.

In Hessel’s presentation, he explained how chitin shells can be used for integrated pest management. Adding chitin to the root zone of plants can help fight pests. It promotes the growth of three organisms in the substrate:

  • Chitinolytic bacteria, bacteria that break down plant-pathogenic fungi.
  • Endophytic microorganisms, microbes that live inside the plant. I hadn’t heard of these, but a quick skim through Wikipedia taught me that they have a symbiotic relationship with plants. Some endophytic microorganisms help plants cope with stress, grow better, and fend off insects and other pathogens.
  • Entomopathogenic fungi, which as the name suggests, fight off insects.

Greenhouse horticulture has so much to gain from deliberately contaminating the plant’s environment with the right organisms. Hessel presented another one of those fascinating discoveries, which also happens to make use of a big waste stream from insect production.

Emily Awuor Okello – Circular Economy Going to Africa?

Emily is a student from Kenya, where the Fall armyworm, an invasive species, is wreaking havoc on corn yields. She started by presenting a flowchart of a circular production system for Africa, the long-term goal of her work.

To achieve this circular vision, however, each production system has to work well. With the Fall armyworm leading to huge losses, this problem has to be tackled first.

At the moment, the main solutions are physical traps on the soil and chemical control methods. Both are expensive, and the latter leads to health problems for people in surrounding communities.

This is where Emily’s work comes in. She is working with Rob van Tol, an entomologist, on a trap based on LEDs. These traps have to work in areas where little electricity is available, so they are trying to make it off-grid. As a bonus, the insects caught in these traps could be used for animal feed.

Those were the six short presentations at Circular Horticulture 2025. Hope you were as intrigued by these ideas as I was.

Many thanks again to everyone who helped organise this event – especially Wouter Verkerke, for giving us students the chance to participate and present!

Left to right: the three students – me, Emily, Cristiana – and Wouter.

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