Soil pH is measured on a scale of 0 to 14, with the ideal range for plant growth from 5.5 (slightly acid) to 7 (neutral). Below 5 is usually classified as very acidic and above 7 is alkaline with above 7.5 very alkaline. Most garden plants prefer a slightly acid soil. Some commonly grown plants that prefer acidic soils include camellias, azaleas, magnolias, many native Australian plants and blueberries. Sweet peas, gerberas, hibiscus, ivy, hebes, roses and many brassica vegetables are a few of the plants that don’t mind a slightly alkaline soil.
Understanding soil pH is important as it not only affects the plants that grow, it also affects the availability of nutrients. As soil becomes more acidic, it may have a deficiency in some trace elements such as calcium, magnesium, and potassium. In soils with high pH (often called limey or ‘sweet’ soil) there’s generally an abundance of sodium, calcium and magnesium however the availability of other nutrients may be limited.
Soil pH can be tested using a pH test kit or as part of a soil test provided by your local garden centre or hardware store. To take samples for testing pH, dig down and take samples from different parts of the garden. Follow the directions given with the soil pH kit to test the sample. Kits also include details on how to alter soil pH if it is too acidic or too alkaline for your preferred plants.
Acid soils can be made less acidic by adding organic compost, manure, leaf litter and Seasol Biochar with Zeolite. Sulphur also works, but it is slow, taking up to six months. To make the soil more alkaline, add a handful of lime per square metre. Changes will take time, they don’t happen overnight, so recheck pH levels over time to monitor changes.
Another option for growing plants where the soil pH is unsuitable is to grow sensitive plants in containers. For example in an area with alkaline soil, grow camellias and azaleas in containers with a premium potting mix such as Seasol Advanced Potting Mix.
Structure is defined as how soil holds or doesn’t hold together. A good soil structure will be soft and crumbly but with particles that hold together well. They allow good air movement as well as providing water and nutrient-holding capacity. Good soils are also full of worm and microbial activity as it’s a great place to call home. Poor soil will not be able to sustain worm and microbial activity as it will not hold together well and may be dry as it will have poor water and nutrient holding capacity. To improve soils, regularly add organic matter such as compost and well-rotted manure and/or Seasol Super Compost or for a no-dig option, apply Seasol Liquid Compost. Alternatively grow a green manure crop that can be dug into the soil. If soil can be rested after adding organic matter then this will also aid the improvement of its structure.