Sand

Sandy soils are low in nutrients and provide excellent drainage, plant roots find it easy to penetrate, delving deeply to where it is cool and moist to resist summer drought, and some liberties can be taken with plants that would otherwise fail in a winter wet climate. On the coast and in the many limestone outcrops the soil will be naturally alkaline, otherwise it is acidic, though this is heavily influenced by the pH of water if irrigating. Apart from the Swan Coastal Plain there are similar soils around the world supporting a similarly high biodiversity, these plants often struggle in heavier soils and with high nutrient loads so beware “improving” the soil too much, it is easier to add than take away. The Fynbos is a fine and famous example offering many popular and climatically appropriate garden plants but you can find white sand supporting parts of the Amazon rainforest and soils home to North American prairies or European meadows are sometimes not so different.

Clay

Common at the base of the Darling scarp and in pockets throughout. Clay soils are much better at holding nutrients and also water. Many classic mediterranean plants can become bourgeois in such an environment but tend to perform better as they get larger and consume excess. Aeration is critically important to plant roots and clay soils do compact easily, especially when wet, so care should be taken to avoid walking in garden beds needlessly, paths solve this and stepping stones or equivalent can be used in deeper spaces. Digging or turning is a tried and tested form of aerating the soil and will be more or less essential for the cultivation of shallow rooted ruderal plants, vegetables and ornamental annuals. In long term plantings digging is almost meaningless as soil will naturally re-compress to its normal state. Most trees and shrubs may take a little longer to establish but shouldn’t have much trouble as long as they are not sitting in water during winter and they’re nursed a bit through the first summer or two. Bulbs and perennials often have thick, sometimes contractile, roots well suited to pushing through heavy soil, whereas those with fine delicate root systems can have a hard time.

Gravel

Found on hilltops throughout the South West. Perhaps the best soil for gardening in our climate, providing essential drainage in winter while retaining nutrients quite well. Pretty much all plants suited to the climate will grow here as long as water and nutrient needs are respected. The only valid complaints of the gravel gardener are the difficulty sometimes in digging and the strangely shaped root vegetables produced.

Laterite

Very common globally, outside of temperate regions, these heavier soils tend to be found further inland in Western Australia where winters are drier and drainage is of less concern than adequate rainfall. Water if available may be saline and better off not being used to create a garden, though there are many halophytes with which to do so, otherwise most mediterranean plants thrive, many even more so than in wetter areas.

Achieving success

Plants, dependent on their environment, are adapted to certain conditions, soil type is but one of them and desperate attempts at changing it will not affect temperature, rainfall or humidity. Conversely plants suited to the climate generally have little trouble with unmolested ground provided just enough nutrients are provided for their specific needs.

The rich organic soil of garden fiction is not to be found in nature, where highly organic soils are nutrient poor and anaerobic, bogs and swamps, with their own accompaniment of specially adapted plants. In a mediterranean climate, with the absence of constant moisture, organic matter is likely to become water repellent, taking a very long time to break down and release nutrients, instead serving to fuel fire that fills the role of decomposition. Too many new and established plants and gardens succumb to whatever latest trend in soil improvement or practice is promoted, an expensive pursuit of some fantastical ideal. If it ain’t broke don’t fix it.

Books

• The Dry Gardening Handbook, Olivier Filippi
• Gardening in South Australia, South Australian Branch of the Mediterranean Garden Society
• Gardens of the Sun, Trevor Nottle
• Good Gardens with Less Water, Kevin Handreck
• The New Ornamental Garden, Simon Rickard
• Plants for a Changing Climate, Trevor Nottle
• Plants for Warm Gardens, 2 volumes, Roger Phillips & Martyn Rix
• Western Weeds, A Guide to the Weeds of Western Australia, B.M.J. Hussy & G.J. Keighery & R.D. Cousens & J. Dodd & S.G. Lloyd