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Fertilisers for native plants in gardens

Nutrients other than nitrogen and phosphorus

Nutrients other than nitrogen and phosphorus

You will have noticed that I have so far discussed only two plant nutrients – nitrogen and phosphorus. What, you might be asking, about all the other four major nutrients and the 8 trace elements?

The other major nutrients are potassium, sulphur, calcium and magnesium.

Our native plants are able to get enough potassium from any soil that has a modest amount of clay. Only on deep sands might there be a need to provide extra potassium. Any controlled-release fertiliser applied at planting will have supplied more. It is unlikely that your plants will need more, unless you repeatedly trim them back and remove the trimmed foliage.

Many South Australian soils contain a good supply of sulphur, in the  form of calcium sulphate (gypsum) that is naturally present in them or has been added. A light application of gypsum (100 g/m2) every couple of years will provide more ‘just in case’ there is not enough present. If you are irrigating with any tap water or water from a dam or bore, you will be adding more (sulphate)-sulphur at each irrigation.

Our plants can get plenty of calcium and magnesium from almost any soil, so long as the pH is above about 5.5. Even though the proportions of calcium and magnesium  can be very different from soil to soil, native plants will be able to choose what they need.

There is one extra thing that can be mentioned about calcium. If you notice that your soil tends to form a crust on drying after rain, chances are that it has too much sodium in relation to calcium. Future crusting can be prevented by applying gypsum (calcium sulphate) to the soil. The extra calcium will displace sodium from the soil clay, so that it can be washed deeply into the soil. Apply about 500 grams per square metre.

Trace elements