Gahnias in your Garden

Saw sedges (Gahnia sp.) are widespread in coastal heath and eucalypt forests in the Noosa area. They are very ornamental, with strappy green foliage, and spikes which are covered in reddish to brownish fruits. Gahnia sp. are butterfly hosts. There are 3 species of Gahnia occurring locally:  Gahnia sieberiana, Gahnia clarkei, and Gahnia aspera.

There are 3 species of Gahnia occurring locally:  Gahnia sieberiana, Gahnia clarkei, and Gahnia aspera.

G. sieberiana (Fig. 1) and G. clarkei are tall, robust sedges, 2-3 m high with flowering spikes rising a further 90cm above the leaves. Both are commonly found in moist coastal heath, sometimes growing side by side! They can be tricky to tell apart. One tell-tale sign of G. sieberiana is that the underside of the leaves is a whitish colour, while G. clarkei leaves are green top and bottom. If you struggle to remember this, think, it snows in Siberia, so G. sieberiana is white on the underside (works for me!). The other difference is the growth form – G. sieberiana grows in clumps, whereas G. clarkei forms colonies via stolons/runners.

G. aspera is a much daintier clumping sedge at only 80cm high with flower spikes not rising above the leaves (see Fig. 2).

All Gahnia sp. make striking architectural plants in the garden and will do best with reasonably consistent moisture. Position plants well back from paths and other access points as the leaves are razor sharp!

Probably the pick of the Gahnia sp. for an urban garden is G. aspera due to its compact size and adaptability to dry conditions. But as luck would have it, germination of G. aspera seed is notoriously slow and unreliable so plants can be hard to find. Coolum Community Native Nursery sometimes sell advanced specimens of G. aspera. The larger Gahnias, G. clarkei and G. sieberiana can be reliably propagated and are readily available at Coolum Community Native Nursery and Noosa and District Landcare Nursery.  They will make a striking feature when planted in a low lying, damp area of the garden, or around a pond.

Sarah Lawson