The low-down on clay soils – Part 4
Knowing your soil pH (potential Hydrogen) before starting to improve your soil is vital, as clay soils can be acid or alkaline. pH will determine how you treat and manage your soil.
The pH of clay soil
Knowing your soil pH (potential Hydrogen) before starting to improve your soil is vital, as clay soils can be acid or alkaline. pH will determine how you treat and manage your soil.
The pH scale runs from 0 to 14 and is used to indicate the relative acidity or alkalinity of the soil, with 7 indicating neutral. pH balance is important because it influences the availability of essential nutrients.
Most horticultural crops will grow satisfactorily in soils of pH between 6 (slightly acid) and 7.5 (slightly alkaline), as nutrients are mostly readily available in this range. Inexpensive pH kits are in stock at most garden centres and hardware stores.
Improving acid/low pH soils
Gardeners should apply liming materials to gardens only after the soil has been tested. There are two types of lime available in South Africa, namely agricultural lime and dolomite agricultural lime (which contains magnesium). Both of these reduce soil acidity and sweeten the soil, provided you follow the manufacturer’s directions for use. The best time to add lime is at least a month before adding any compost, manure or organic fertilisers.
Lime will neutralise acidity, encouraging earthworms and beneficial bacteria. It contains calcium, which is essential for plant growth and acts as a catalyst which releases other nutrients bound in the clay. Lime improves acidic clay soil by making the clay particles collect into clumps, thus improving drainage. The amount of lime you use depends on the results of your pH test. Test your soil again after a year and only add lime if necessary.
If your soil is very alkaline, never add lime but rather gypsum.
