Mastering fertilization in the shift to peat-free growing

Fertilization strategies must be carefully aligned with the alternative raw materials in use, especially when it comes to maintaining sufficient nitrogen and calcium levels. Lianne van Wijk, ICL’s International Technical Manager for Ornamental Horticulture, shares practical insights on how to develop the right fertilization approach and highlights tailored solutions designed to support growers through this transition.

For many years, peat has been the dominant raw material in substrates for pot plants and nursery crops. But due to the environmental impact of peat extraction, its use is coming under increasing pressure.

“Growers in Europe, and far beyond, will inevitably need to reduce or eliminate peat in their growing media,” says Lianne. “And many have already made substantial progress in this direction. Wood fiber and coir are currently the most widely used alternatives.”

Peat-free cultivation requires precision

Lianne acknowledges that working with substrates that contain little or no peat is a complex undertaking. “Peat has very specific properties. It offers excellent buffering capacity, retaining both moisture and nutrients. On top of that, the lime blended with peat during potting soil production helps maintain a stable pH.”

Many alternative materials don’t offer the same buffering capacity for water, nutrients, or pH. This means fertilization strategies need to be adjusted accordingly. “The right approach depends entirely on the specific alternative materials you’re working with. There’s no one-size-fits-all solution. It really is precision work, and that’s what makes it so complex.”

ICL’s International Technical Manager for Ornamental Horticulture Lianne van Wijk

Nitrogen needs extra attention

That said, Lianne does share some key takeaways. Nitrogen management, for example, is crucial when using low-peat or peat-free substrates. “Many alternatives, like wood fiber, tend to tie up nitrogen during their decomposition process,” she explains. “As a result, you need to be extra vigilant to ensure nitrogen levels stay sufficient. Additionally, alternatives like wood fiber and bark retain less water, which means nutrients are washed out more quickly. So, more frequent watering, and fertilization, is essential. As a general rule, we recommend increasing Osmocote dosage by around 20%.”

Alternative fertilizers in development

ICL Growing Solutions supports growers in multiple ways throughout this transition. One way is through expert advice on adjusting fertilization and trialing different fertilization strategies. Another is through investment in the development of new fertilization products.

“For instance, we now offer a controlled-release nitrogen fertilizer that delivers nitrogen over five to six months,” Lianne says. “With alternative materials, it becomes increasingly important to supply extra nitrogen throughout the growing season because of the higher risk of nutrient leaching.”

One upcoming CRF innovation is a nitrogen product with a biodegradable coating. “This is in anticipation of the 2028 legislation requiring that all coated fertilizers fully degrade within four years after their release period.”

In parallel, ICL Growing Solutions is developing new calcium solutions. “Peat-based mixes are typically blended with lime to raise the pH, but that’s not the case with many alternatives. That’s why an additional calcium input is often necessary.”

A complete nutrition plan

While nitrogen and calcium are key focus points, Van Wijk emphasizes the importance of considering the full nutritional picture. “Everything has to be in balance. You also need to watch potassium and phosphate levels, and don’t underestimate the role of micronutrients. This is advanced fertilization—understanding micronutrient levels requires detailed knowledge of your substrate’s exact composition.”

Substrate sampling is essential

Her advice for growers experimenting with (partially) peat-free substrates: take regular substrate samples.

“Start with a baseline sample at the beginning of the growing cycle. That gives you a reference point. Continue sampling during the crop cycle so you can monitor how nutrient levels evolve and adjust accordingly. Don’t forget to sample your irrigation water too—and align your fertilization strategy with the results. Because at the end of the day, measuring is knowing.”