The availability and uptake of nutrient ions are influenced by the pH of a substrate, which is a measurement of the level of acidity or alkalinity of the medium. Most crops grow best in soilless media when the pH in the root zone is between 5.5 and 6.5. Some trace elements, including iron and zinc, as well as macro elements, like phosphate, may have decreased uptake at high pH values, leading to an induced deficit.
To achieve the proper pH levels for optimum plant growth, the growing medium ingredients might have a wide range of pH values. Depending on the degree of decomposition, peat normally has a low pH in the range of pH 3–4, and peat-based substrates are treated with lime to modify the pH as necessary.
Dolomitic lime, which is applied at rates of 2 to 3 kg/m3 for less-decomposed (H2-H3) peat and 3 to 7 kg/m3 for more-decomposed (H4-H6) peat, also delivers calcium and magnesium. (Maher et al., 2008).
The pH of coconut fiber, including coir dust, fines, and chips, is often suitable between 5.5 and 6.5 and doesn’t need to be adjusted.After composting, pine and other bark typically has a pH between 5.0 and 6.5. Lime may be added to some composted bark substrates as needed to raise the pH. (Jackson et al., 2009).