02/05/2026
Today, before rain made me pack up I was wanting tk know what would be causing one of the Grevilleas I have planted to go a fleuro colour.
Too much phosphorus (P) and you will have a very unhappy native. Plants like Grevilleas, Banksias, and Hakeas because they're used to low-phosphorus soils and can't handle too much of it. It basically burns their roots, making their young leaves turn yellow, leaf tips brown, and often kills them.
High pH (alkaline soil) is also a problem because it makes iron, manganese, and phosphorus unavailable for plants to absorb. Natives usually need acidic soil (pH 5.5–6.5), so if the soil's too alkaline, they can't get enough iron, and their new leaves turn yellow.
How to fix this issue.
Add Iron Chelates: Apply iron chelates to the soil or as a foliage spray, which can "steal" the excess phosphorus and immediately feed the plant.Acidify Soil: If the pH is high, use iron sulphate to lower the pH, making nutrients more available.Avoid Certain Organic Matter: Avoid adding manure or high-phosphorus composts around sensitive natives.