Faster breeding thanks to a heated greenhouse

Since 2023, De Bolster has not only had cold greenhouses for breeding, but also a heated greenhouse. Frans Carree, head of the Breeding Department: “This greenhouse offers all kinds of new opportunities, but also brings challenges.” This is because the greenhouse was previously used by a conventional grower.

“Thanks to the heated greenhouse, we can breed and react to the market much faster”

When Frans joined De Bolster in 2017, he quickly concluded that what they were breeding in the cold greenhouse was not suitable for cultivation in heated greenhouses. If De Bolster wanted to develop further and expand into that sector, they had to select and breed varieties under those same warm conditions. And so, in 2017, the company went in search of a heated greenhouse.

The first trials

De Bolster soon got in touch with conventional cucumber grower Willem Doorn, who had a beautiful 1.5-hectare greenhouse practically around the corner in the village of Heerde. He was willing to free up a section of 250m². In 2018, the first tomato trials were planted in the greenhouse. Frans immediately saw a difference in the selection. “You sow in November and plant out in January, at a time when there is very little natural light. This means a completely different plant type emerges, with more leaves and fewer trusses. Selecting for this is therefore essential if the plant is to be suitable for growers with heated greenhouses.”

Slowly but surely, plans began to take shape to eventually take over the greenhouse, allowing De Bolster to invest more in breeding for heated greenhouse vegetables.

“We had the soil tested, and it turned out to contain a significant amount of pesticide residues, even from substances that have been banned since 1978”

Pesticides in the soil

It was a massive shock – both personally and professionally – when the grower suddenly passed away in 2022. The entire plan to take over the greenhouse fell through. The greenhouse was put up for sale and bought by a neighbor of the grower. Fortunately, a solution was found fairly quickly: De Bolster was allowed to rent the greenhouse, and in 2023 Frans and his team could officially get started. It wasn’t without its challenges. “We had the soil tested, and it turned out to contain a significant amount of pesticide residues, even from substances that have been banned since 1978. That’s how long they stay in the ground. Just look at PFAS, which we as a society are being confronted with today.”

In 2024, the first small-scale trials were planted to see if the pesticides could also be detected in the plant, the fruit, and the seed. The result? All crops in the nightshade family (which includes tomatoes and peppers) were clean, but residues were found in the cucurbit family (cucumbers, pumpkins, and zucchinis). This means that, for the time being, seed production is not possible for that family of crops.

Bringing the soil to life

The soil in the greenhouse—which had been covered in plastic for twenty years—contained almost no life. This meant a major investment was needed to get the soil healthy again. Frans: “We added a lot of compost and bought 150 kilos of earthworms to improve the fertility and structure of the soil. The great thing is that worms can also break down certain chemical pesticides. We are constantly monitoring how many residues we still find in the plants. Fortunately, those levels are dropping, and we hope to use the greenhouse in the future for propagating crops like pumpkins, zucchinis, and cucumbers. It’s a process of many years, but it really feels like we have saved this soil.”

“In the heated greenhouse, we can develop much more robust varieties that perform well under all kinds of conditions”

Propagating plants year-round

This year, De Bolster is using 3,000m² of the 15,000m² greenhouse. This section is currently dedicated to tomato selection, rootstocks, and a few small projects. Frans: “The big advantage of a heated greenhouse is that you can use it year-round and grow not just one, but two or even three generations of a crop in a single calendar year. This allows you to breed much faster and introduce new varieties sooner.”

For now, the greenhouse is being used purely for selection and breeding, not yet for seed production. Frans: “We definitely want to do that in the future. It will allow us to propagate crops year-round, which opens up fantastic opportunities. In addition to faster breeding, we can respond more quickly to seed availability. For example, if a variety proves popular with growers, we can immediately produce more seeds and don’t have to wait six months for the right season. That is where our real strength lies.”

Opportunities for growth

Frans hopes the heated greenhouse will grow along with the company and eventually be fully utilized. He concludes: “What I love is that in this greenhouse, we can develop much more robust varieties that perform well under various conditions, both in heated and unheated cultivation. This offers us excellent opportunities for further growth.”

Phasing out natural gas

The greenhouse in Heerde is currently still heated by a pipe system filled with warm water that runs throughout the entire greenhouse. The water is heated by a boiler and a CHP (combined heat and power) unit. This allows us to heat the greenhouse to a comfortable temperature in winter. In the future, De Bolster wants to transition away from gas, but for now, the focus is on cleaning up the soil in the greenhouse.