Trials with peat-free substrate yield surprisingly good results |
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'Despite sensitive Acer roots, little difference was noticed'
Last year, the innovation circle Weerbaarheid in de Praktijk Zundert (LTO Trees, Perennials and Summer Flowers) set up five practical trials using peat-free substrate. This was done in collaboration with BCT Treeport, Varta Valorisatielab, GroeiBalans and substrate producers. Patrick Braspenning from Boomkwekerij J. Bevers & Zn and substrate producer Legro also participated. 'Our main product, Acer, has sensitive roots,' says the grower. 'Yet, I saw no difference in results and didn't have to adjust my methods. In May, we'll repeat the trial to gain even more experience.'
| Grower Patrick Braspenning continues the trial this spring. |
Patrick Braspenning didn't need long to think about the invitation to participate in the trials. 'We supply a lot to the English market, which is known for its critical stance on peat,' explains the grower from Wernhout. 'You read about it everywhere, but so far not a single customer has asked us to switch to peat-free substrate. Thus, I prefer sticking to my trusted peat mixture. I know it thoroughly, and plants with sensitive roots, such as Acer, thrive perfectly in peat.'
Opportunity to gain experience
The tree grower realizes, however, that at some point he will have to switch to substrates composed mainly of renewable materials, such as coconut fibre and wood fibre. Even if his British customers do not ask for it, this necessity emerges from the Dutch substrate covenant. The agreements stipulated therein foresee a gradual increase in the use of renewable raw materials with a smaller environmental footprint. 'It's only a matter of time. We'll have to make the step eventually, and it's easier when you've already done your homework,' continues Braspenning. 'Participating in this project, for me, was mainly an opportunity.'
Renewable raw materials
For producer Legro from Helmond, the project provided an opportunity to give its loyal customer experience with sustainable substrates, something the company has been familiar with for years. 'We have historically been linked to peat, but have also processed renewable raw materials such as coconut and wood fibre for a long time,' says substrate advisor Tim Heestermans. 'Legro was even one of the first companies to import coconut fibre on a large scale and has its own production sites in India and Sri Lanka. There, we pay a lot of attention to sustainability and quality assurance. Many of our customers, including those in tree nurseries, have switched in recent years to mixtures with less peat and more renewable raw materials. This works fine, as long as growers are aware of the specific characteristics and differences compared to 100 percent peat. Differences always exist to some degree, but that should not be an obstacle for change. It's great that Boomkwekerij J. Bevers wanted to collaborate on this project. The trials were supervised by Varta and GroeiBalans, further boosting grower confidence.'
No wet feet
Braspenning and his team grow garden plants in container sizes C4 to C90. Acer, Hamamelis, Magnolia and Syringa are the main varieties. As the grower mentioned, especially Acer has high demands for the substrate. 'Japanese maples don't like wet feet,' he explains. 'If it stays too wet and cold at the bottom of the pot, you face issues such as growth delays, root death and soil-related diseases. The substrate must therefore contain enough air and be able to hold water. Good drainage is essential.'
For the trial, Legro composed a substrate from renewable raw materials, coconut and wood fibre, supplemented with perlite. From spring onwards, this was tested alongside the traditional peat mixture. The base fertilization was adapted to plant needs and substrate characteristics, such as pH and buffering capacity for water and nutrients. Tim Heestermans: 'Peat has excellent buffering properties and is very stable. With the alternative mixture, we aim to approach these characteristics closely while maintaining high, consistent quality. For longer crops, that's truly essential. Generally, peat-free substrates tend to be somewhat drier than pure peat, requiring adjustments in watering and fertilization. At Bevers, however, this was hardly necessary due to regular rainfall.'
Expectations exceeded
Braspenning confirms that the trial results exceeded his expectations. 'I was pleasantly surprised. Previously, without Legro's involvement, I had conducted a small-scale test with a different substrate mixture, and the plants did not respond well. With Legro, Varta and GroeiBalans involved, I had more confidence. You often hear that substantial adjustments are required when growing with peat-free substrates, but due to abundant rainfall, this was hardly needed. Root development in the peat-free mixture was even slightly faster during the initial growth phase, producing more fine roots, which I prefer since they support plant growth. Above ground, no visual differences appeared. For me, this mixture passed with flying colours.'
A visual assessment took place on 5 June (left) and 9 August (middle). Containers with blue labels contain peat; purple indicates the alternative substrate. At the bottom of the root ball, it's clearly visible that the alternative substrate provides good drainage.
Continuing the trial
The grower notes that 2024 was a relatively wet, productive year. 'If the circular substrate was drier, that wasn't evident due to the weather. On the other hand, we now also know drainage is not an issue. Our Acers grew very well. I expect we can move towards sustainable substrate with this mixture, but I'm not fully switching yet. We'll repeat the trial with both substrates in May. If we get a dry, hot summer, any differences will likely become clearer. I honestly hope for that, so I can learn how to manage it. Legro, Varta and GroeiBalans remain involved. I'm curious how it goes.'
Heestermans also looks forward to it. 'We gladly share our knowledge and experience with our customers, but growers control the process. Potting methods, watering frequency, and fertilization affect the substrate's physical, chemical, and biological properties. Growers who invest time to understand a new substrate, ideally in a controllable setting, will have little trouble adapting, even under variable weather conditions. Regular evaluations with cultivation and substrate specialists also help.'
René van Gastel: 'Look at analyses and act accordingly'
The trials with circular substrate are technically guided by cultivation advisor René van Gastel from GroeiBalans. 'Together with Varta, we visited the trials monthly and assessed visually, also underground. Varta also took samples for analyses. Legro's mixture undoubtedly performed well. The main component is coconut, already widely used in tree nurseries and perennial cultivation. Perlite is also a well-known ingredient, particularly useful for improving drainage and ensuring a good air-water balance in containers.'
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Occasionally, analyses revealed small differences. 'If you're aware of these and act accordingly, it's not a problem at all,' says Van Gastel, who concludes with an important message: 'Realize that each substrate mixture behaves differently, requiring adjustments in cultivation. Growers who used peat mixtures almost on autopilot will need to switch off that mindset and truly pay close attention. This means more frequent measurements, closely studying analyses, and taking the necessary steps to maintain optimal root-zone conditions.'
This article was previously published on 18 April 2025 on the Boom In Business website.
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