Soil pH-un

SERIES 33 | Episode 14

Tino Carnevale shows how to test the pH of your soil and digs deeper into what it means for your plants.  

Healthy plants need healthy soil that can hold and supply the right amount of moisture and nutrients. The pH of soil is the measure of alkalinity or acidity of the soil, or in technical terms, the amount of hydrogen ions present. It can vary depending on where you live or how soil has been managed, and it can affect the type and amount of nutrients plants can access.

Testing Soil pH

The easiest way to measure your soil pH is to use a pH test kit from your local nursery.

Whilst pH can range from 1 to 14, the kit contains a scale from 2 to 10 which is the range you can find in soil.

Follow the instructions in the kit to collect a soil sample free of rocks and twigs, add the dye and barium powder. The colour will indicate the pH number on the scale. 

Testing top tips:

• Test multiple samples from different parts of your garden as the pH can vary

• Wait for dry weather to improve accuracy of results

• Test soil before adding organic matter or minerals

Neutral pH

A pH close to 7 is ideal for most vegetable gardens as the most important nutrients of nitrogen, phosphorus and potassium are readily available for the plants to uptake. If the pH is too acidic or alkaline, your vegies may have yellowing leaves or stunted growth and become more susceptible to diseases.

Acidic pH

Acid-loving plants like waratahs, rhododendrons, blueberries, and camellias prefer pH to be between 5-6.5. Acidic in this case does not mean a pH of 1 or 2, that would be battery acid! The pH scale is logarithmic, which means that there’s a big difference between each number – a pH of 6 is ten times more acidic than a pH of 7.

To acidify soil, add compost, manure, and mulch.

Alkaline pH

A pH of 7-8 is perfect for brassicas, garlic, spinach, hibiscus, sweet peas and geraniums. All the major elements plus more calcium and magnesium are available. To make soil more alkaline, add dolomite or garden lime to soil. Clay soils will need more added than sandy soils.

Around the country

There are general patterns of pH around Australia, based on the type of underlying bedrock, rainfall, and agricultural usage. For example, most of Western Australia’s coastal regions tend towards alkaline soil due to limestone; Tasmania’s east coast is dominated by dolerite clays that forms neutral to acidic pH soils; and two-thirds of Queensland’s soils are acidic due to high rainfall. Generally, dry areas are more alkaline as elements in the soil are more stable. Fifty per cent of our agricultural lands have high acidity due to practices like using ammonia-heavy fertilisers.

Crop rotation can also help with ensuring plants get the nutrients they need, or you could try choosing indigenous plants that are suited to your local soils. Keep an eye out for signs of nutrient deficiencies, test your soil, and amend it if needed. And consider choosing plants that are already suited to your soil type and its pH to save yourself time and money in the long run!

Filmed on Muwinina Country | Hobart, Tas