This recipe is from Kevin Handreck’s excellent book Gardening Down Under, CSIRO 2001.
Lightly moisten 10 litres of compost or animal manure and mix in one cup of iron sulphate.
Dig holes about 20cm deep in the plant’s root zone. Three for a rose bush or 6-8 for a big grevillea. Put the iron compost into the holes and water well.
The plant roots will soon grow into the organic matter. The treatment lasts for several years, unless the irrigation water is highly alkaline.