Water-soluble Fertilizers and New Growing Media

Greater Nutrient Leaching Risk

New growing media based on woodfibre, bark and coir behave differently from traditional peat‑based mixes. Their lower water‑holding capacity means less water remains in the pot at field capacity. Combined with a lower cation exchange capacity (CEC), which reduces the media’s ability to retain nutrients on its surface, the risk of nutrient leaching significantly increases.

How to Reduce Nutrient Leaching

Several cultural and irrigation adjustments can help growers minimize losses and maintain nutrient availability.

Irrigation method

• Overhead irrigation causes the highest leaching.
• Drip and capillary irrigation are far more efficient and reduce nutrient loss.

Pot spacing

• Overhead irrigation with spaced pots is highly inefficient.
• Switching to drip irrigation improves uniformity and reduces waste.

Irrigation controlling

• Use shorter, more frequent irrigation cycles to reduce leaching and lower input costs.
• Monitor pot moisture closely and irrigate only when needed.
• Sustainable media often appear dry on the surface, so lifting pots to assess weight is a fast way to judge moisture.

Use of wetting agents

• Wetting agents such as H2Gro improve water distribution and increase the water‑holding capacity of sustainable media.
• Better rewetting reduces both water use and the amount of water‑soluble fertilizer required.

Deficiency Symptoms in New Growing Media

Woodfibre, bark and coir-based growing media typically require far less lime than peat to reach the correct pH. As a result, baseline levels of calcium (Ca) and magnesium (Mg) in the substrate are lower. When combined with soft water (naturally low in essential nutrients), the risk of nutrient deficiencies increases.

Calcium deficiency

Calcium is immobile within the plant, so symptoms appear in young leaves and growing tips. Typical signs include:

• Cupping or distortion of new leaves
• Browning or necrosis at the leaf margins
• Weak or stunted new growth

Magnesium deficiency

Magnesium is mobile, so symptoms develop first in older leaves. Look for:

• Interveinal chlorosis (yellowing between veins)
• Gradual fading of leaf colour while veins remain green

Iron deficiency (common in hard water situations)

In new growing media with low CEC, high bicarbonate levels in hard water can raise pH above the optimal 5.5–6.0 range. As pH increases, iron availability drops. Iron is immobile, so symptoms appear in new leaves:

• Interveinal chlorosis in young foliage
• Pale or bleached new growth
• Symptoms resembling magnesium deficiency, but located in the newest leaves

Nutrient Management Solutions

For soft water

Soft water supplies little calcium and magnesium, so feeding programmes must compensate. Suitable fertilizers include:

• Universol Soft Water (three formulations for different growth stages)
• Peters Excel CalMag Grower or Peters Excel CalMag Finisher

To correct an active Ca or Mg deficiency, apply Peters Foliar Feed for rapid uptake and visible improvement.

For hard water

Hard water can push substrate pH too high, reducing iron availability. To prevent iron deficiency:

• Use Universol Hard Water or Peters Excel Hard Water as part of the regular feeding programme
• Apply Peters Foliar Feed to quickly correct an existing iron deficiency

Support from the ICL Technical Team

ICL technical team works closely with growers to optimize nutrient strategies for new growing media. Using AngelaWeb 3.0, our precision nutrition software, we analyze key factors such as crop demand, water quality and growing media composition to create tailored feeding programs. These customized plans combine water‑soluble and controlled‑release fertilizers where appropriate, helping growers maintain crop quality, reduce nutrient losses and achieve consistent results throughout the season.

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.