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Soil and Plant Nutrients

Soil structure

Whether you are just starting a garden or preparing to renew an old one, start with soil preparation.

Firstly, look at the soil structure.

On the Surf Coast, it is likely your soil will be either very fine sandy soil that turns to dust when you rub it in your hand, or heavy clay. In both cases the soil is made up of very fine particles.

Whether you have sandy soil or clay soil, you can improve the structure of your soil by adding coarse propagating sand and organic matter.

Adding coarse sand will improve water and root penetration. Adding organic matter to the soil will increase its nutrient  value, for both plants and beneficial soil microbes, and also water holding ability.

Soil pH

What is soil pH?

Soil pH is a measure of the level of acidity or alkalinity of the soil. Soil pH is measured on a scale of 0 to 14. A pH value of 7 indicates neutrality, while a value of less than 7 indicates acidity and a value over 7 indicates alkalinity. Soil pH can easily be measured using a soil pH test kit.

Why is soil pH important?
Soil pH can have a dramatic impact on plant growth because it affects the availability of essential  nutrients in the soil. Different nutrients become available at different pH values.

Some plants grow well in acidic soils, some thrive in alkaline soils while others grow better in neutral soils as the nutrients they require are available at different pH values.

Plant Nutrients

In order to grow, all plants require a combination of chemical elements. Three of these, carbon (C), hydrogen (H) and oxygen (O) are obtained from carbon dioxide from the air and water.

These elements will be available to plants, provided an adequate water and air supply is present.

The other elements required by plants are mostly obtained from the media in which they are growing. If the soil or potting mix is deficient in nutrients, you will need to provide them in the form of fertiliser or organic matter.

Nutrient elements can be categorised into two groups based on whether they are required in larger or smaller quantities.

The major elements

Nitrogen (N) boosts the protein content of all plants and increases growth in leaf crops such as turf, lettuce and cabbage. Nitrogen is part of chlorophyll which is essential for photosynthesis. Deficiency symptoms include yellow leaves, stunted growth and burning of leaves.

Phosphorus (P) makes plants hardy, stimulates root formation and assists the production of flowers, fruit and seeds. Deficiency is indicated by weak roots, spindly growth, delayed maturity and no flowers and fruit production. Plants in the Proteaceae family, including Australian natives such as Grevilleas and Banksias and South African plants such as Proteas and Leucadendrons, are particularly efficient at extracting phosphorus from the soil and can suffer from phosphorus toxicity.

Potassium (K) also called potash, aids in the production of plant starches and sugars. Potassium plays an important role in helping plants resist disease aiding in the development of thick outer cell walls. It also helps to regulate water loss. Potassium deficiency can present as brown scorching and curling of leaf tips, and yellowing of leaf veins. Plants may also be prone to disease and frost damage. Fruit development may also be irregular.

Sulphur (S) improves resistance to cold and disease and is also important in root formation and seed production.

Calcium (Ca) is also vital for root growth.

Magnesium (Mg) is part of chlorophyll which is essential for photosynthesis. It also activates many of the enzymes needed for plant growth.

Trace elements

The availability of trace elements in small amounts is essential to healthy plant growth.

Manganese, Iron, Copper, Zinc, Boron and Molybdenum assist plants to absorb and utilise the major elements. Nearly all gardens on the Surf Coast are deficient in trace elements.