Cal-BOOST Slow-Release Fertiliser for sustainable Growing Media

Recommended for pot plants, such as calcium hungry Poinsettias, fast-growing perennials and container nursery stock, ICL launched its next generation slow-release starter fertiliser, Cal-BOOST at the HTA National Plant Show.

A new mini-granule product with proven biodegradable coatings, Cal-BOOST (20-5-5+7CaO+2MgO) is formulated for sustainable growing media mixes. Steadily releasing nitrogen (urea) over a 2-3month period, it delivers calcium, magnesium and potassium over a 6-8week period.

Managing Calcium and Magnesium Deficiencies in Peat-Free Mixes

“As substrates evolve, the peat content is being reduced or eliminated,” says ICL Technical Manager, Andrew Wilson. “These new mixes require less lime – specifically calcium and magnesium carbonates – to optimise pH, and therefore nutrient delivery.   This can lead to calcium and magnesium deficiencies.

“These nutrient deficiency issues can be exacerbated under soft water irrigation regimes, or in calcium hungry crops – such as Poinsettias. In addition, many wood-based peat alternatives can contribute to nitrogen drawdown within the substrate, reducing nutrient availability during early crop establishment.”

To address these challenges, Cal-BOOST delivers a combined supply of controlled-release nitrogen plus slow-release calcium, magnesium, potassium and sulphur. This balanced formulation promotes more uniform nutrient availability, supporting stronger, more resilient plant growth while helping to mitigate nitrogen immobilisation in sustainable mixes.

Simpler and more sustainable, Cal-BOOST replaces Osmocote CalMag, which was withdrawn due to technical manufacturing constraints.

Next-Generation Fertilisers with Biodegradable Coatings

“Cal-BOOST is the latest addition to ICL’s expanding pipeline of sustainable fertiliser innovations incorporating biodegradable coating technologies,” adds Andrew. “Next year we plan to introduce Osmocote N-Boost, a next-generation controlled-release fertiliser featuring a biodegradable coating. Osmocote N-Boost is specifically formulated for high-demand nursery stock, such as evergreens.”

In parallel, and in anticipation of forthcoming EU regulatory developments, ICL continues to advance the development of biodegradable coating systems for its established Osmocote controlled-release fertiliser range, reinforcing its commitment to more sustainable horticultural nutrient management solutions.