Water Quality and Calcium Uptake in New Substrates

Why is Calcium Supply Low in New Substrates

Peat‑free and peat‑reduced substrates typically contain less incorporated lime, which means they provide lower levels of plant‑available calcium. Crops with high calcium demand are therefore more likely to develop deficiencies – often before visible symptoms appear. To prevent these situations it is advisable to take special attention when growing crops with high-calcium demand, for example:

• Boxwood
• Camellia
• Hibiscus
• Erica gracilis
• Primula
• Roses

Also young plants may develop calcium deficiency during winter months when transpiration is reduced. Calcium deficiency is often recognized too late, and symptoms cannot be reversed.

Why Water Quality Matters for Calcium Uptake

We have dedicated an article to the interaction between water quality and fertilization approach in new substrates. Now let’s dig into calcium uptake which entirely depends on plant’s ability to move water through the transpiration stream, which makes it highly sensitive to the chemical composition of irrigation water.

Elevated soluble salts (high EC) can damage root tips and reduce water flow, limiting the transport of calcium to young tissues. Water with high alkalinity or bicarbonate levels gradually raises substrate pH, which decreases calcium solubility and can cause it to precipitate with carbonates or phosphates, making it unavailable for uptake. In addition, excess sodium, potassium, or ammonium in irrigation water competes with calcium at the root surface, further reducing absorption.

To learn more about EC and salt measurements on peat-based substrates vs peat alternatives, click here

How to Ensure Calcium Availability in Peat-Free or Peat-Reduced Substrates

Because calcium-deficient situations happen more quickly in peat‑free and peat‑reduced substrates with low buffering capacity, regular water analysis is essential. It allows to make early interventions to stabilize pH and also helps when choosing the best water-soluble fertilizer. To ensure sufficient calcium supply it is advisable to use ICL’s formulas designed for soft water from the  Peters® Excel (7% Ca) or Universol® (6% Ca) range.

Adding Cal-BOOST as base fertilizer is another good strategy to ensure calcium availability.

Conclusion

ICL offers proven fertilization strategies for new substrates and provides expert guidance through its specialists. For personalized guidance, contact your regional technical support by visiting your country’s website or fill in the form you can reach from the banner at the bottom of this page.