By Kate Wall
Clay soils can be very heavy and hard to dig, with a tendency towards water logging. While heavy clay soils will need significant improvement before most plants will happily grow in them, moderate to light clay soils can be very suitable for a wide range of plants, providing that the drainage is adequate. Improved clay soils can hold nutrients well and therefore can be very beneficial to plants which like a lot of water and nutrient, including many large leaved or tropical plants.
As clay soils can tend to water log easily, care should be taken with garden design to allow for good drainage. Few plants are tolerant of water logged soils.
Most of the iconic Australian native plants prefer free draining soils, and will struggle in clay soils without adequate drainage and some soil improvement. Gold Cluster™ Grevillea juniperina ‘H22’ PBR is a ground cover grevillea which will perform well in moderately heavy soils.
Yareena™ Myoporum parvifolium ‘PARV01’ PBR is another native ground cover tolerant of a wide range of soil types, including heavy clay.
Shallow rooted plants, such as many ground covers can do well in heavy clay soils where there is sufficient loamy top soil to prevent water logging of shallow roots. The same can apply to shallow rooted shrubs such as Azaleas. Improving the top layer of soil sufficiently can be of great benefit to these plants as the clay subsoil will hold moisture and nutrient, making them more drought hardy and requiring less fertilising than if they were growing in sandy soils.
Flowering native shrubs such as Leptospermums, Callistemons, Melaleucas, many Acacias and Hoveas are also tolerant of moderate clay soils. Banksia spinulosa and Banksia ericifolia are also very tolerant of clay soils.
Although Westringias tend to prefer free draining soils, they are very tolerant of light to moderate clay soils. The Ozbreed range of Westringias offers a variety of forms which will have something to suit almost any garden, from neat compact bushes with a natural ball shape, such as Grey Box™ Westringia fruticosa ‘WES04’ PBR, to Mundi™ Westringia fruticosa ‘WES05’ PBR, a spreading ground cover with masses of white flowers to Naringa™ Westringia ‘WES01’ PBR which is a perfect low maintenance hedge.
The strappy leafed Lomandras and Dianellas are tolerant of all but the heaviest clay soils.
Blaze™ Dianella tasmanica ‘NPW2’ PBR and Lucia™ Dianella caerulea ‘DC101’ PBR are amongst the best dianellas for clay soils. Most Lomandras are very tolerant of clay soils and amongst those highly recommended are Lomandra longifolia 'Katrinus Deluxe' PBR for abundant flowers and Lucky Stripe™ Lomandra hystrix ‘LMV200’ PBR which is a very hardy variegated strap leafed plant suited to clay soils.
Amongst the ornamental grasses, Pennisetum do well in clay soils. The invasive introduced species are best avoided and instead grow some of the lovely native species. Ozbreed have developed some beautiful varieties of native Pennisetum with wider flower plumes and neater growth habits, including the beautifully compact Nafray® Pennisetum alopecuroides ‘PA300’ PBR, the smaller variegated form Pennstripe™ Pennisetum alopecuroides ‘PAV300’ PBR and the larger Purple Lea® Pennisetum alopecuroides ‘PA400’ PBR with purple flower heads.
Lilly Pillies are well suited to moderate clay soils and in particular Red Head™ Acmena smithii ‘BWNRED’ PBR with its red coloured new foliage, and Sublime™ Acmena smithii ‘DOW30’ PBR with lime green new foliage are reliable choices for hedges or screens in clay soils.
Many garden favourites, including day lily, golden rod, coreopsis, rudbeckia, sea holly, brusfelsia, many hibiscus (native and otherwise), cannas and acalyphas will all do well in clay soils. A number of the ornamental salvias are also highly tolerant of clay soils. Double Gold™ Gazania hybrid ‘GT20’ PBR is tolerant of even heavy clay soils and has the advantage of being sterile so will not become an environmental weed.
Nandinas are also very tolerant of clay soils and there are many varieties to choose from. Blush™ Nandina domestica ‘AKA’ PBR is low growing and produces new red foliage all year. Flirt™ Nandina domestica ‘MURASAKI’ PBR is a ground cover form, and Obsession™ Nandina domestica ‘SEIKA’ PBR is a mid-sized form which is ideal for low hedges and features red growth for much of the year.
With improvement, clay soils can be very valuable to the gardener, requiring less water and fertiliser to maintain than sandy soils. With good attention to drainage these soils will grow a wide range of plants very well. Further information on how to improve clay soils can be found here.