Proteas prefer a nice sandy loam or open soil. Some Proteas are less fussy and are quite happy in a heavier soil although they will not survive in heavy clay soils. If you do have heavy soils it will be necessary to first mound the soil to improve it and then dig in compost and gypsum to break up any residual clay.

pH or the acidity or alkalinity of soils. Plants often grow best where the soil pH is similar to their conditions of origin. Proteas prefer to grow in acidic soils as this reflects the conditions where they originate in South Africa and Australia. The majority of Proteaflora products need an acidic soil with a pH between 5.6 and 6.5. Some of our products do tolerate neutral to alkaline soils with a pH between 6.6 to 7.5. If that's a bit confusing, your local nursery should be able to tell you about your local soil and advise you on testing and treatment, if necessary. Check out the Our Plants page to find the plants best suited for your garden.

http://www.proteaflora.com.au/establishing-your-new-protea.html