Oyster Plant Acanthus mollis

Plant oyster plant where you are happy for it to stay. It grows from thick fleshy roots into a spreading clump of broad, deeply lobed, glossy leaves long enough to arch out over a path, and sends flower spikes well above them, hooded white blooms backed by dusky purple bracts. This is the leaf carved into Corinthian columns, which shows how long gardeners have tolerated its habits. Its real value here is dry shade under established trees, where tree roots leave most perennials thin and this one still looks lush.

Dry shade, snails and summer

Part shade is what it asks for, and it will take fairly deep shade beneath a dense canopy. Soil is not a fussy matter provided it is not permanently wet, and a bed improved with compost gives the largest leaves. Water is moderate, with regular watering through summer the difference between a clump that stays presentable and one that browns off and retreats until the weather cools. Growth is moderate and steady, and a single plant covers a surprising area within a couple of seasons, so set plants well apart in a border rather than massing them tightly. Snails and slugs shred the new leaves in spring and will ruin the display if left to it.

The real problem is removal. Every fragment of root left in the ground sends up a new shoot, so digging a clump out usually multiplies it, and long established plantings in Victorian and South Australian gardens have earned the species a reputation as a garden thug. Keep it inside an edged bed, well away from garden boundaries, and think twice before running a rotary hoe anywhere near it.

Bold foliage without the frost risk

The other big leaved plant in this batch is variegated shell ginger, and the split between them is climate. Shell ginger gives brighter, striped foliage and a tropical read, but frost burns it and cold wind shreds it, so south of the subtropics it needs a warm wall or a pot. Acanthus handles frost, handles dry shade and asks for far less, at the cost of being difficult to remove later. Gardeners in Melbourne, Adelaide or Canberra should take the acanthus without much hesitation. If you want structural foliage in an open sunny bed instead of shade, Dietes grandiflora is the strappy alternative that takes exposure and mass planting. Browse the flowering range for other options.

Cutting back the spent spikes

Cut flower spikes off at the base once the last blooms have gone over, and do it before the capsules split and fling seed across the bed, unless seedlings are what you are after. Pull or cut tired outer leaves at ground level through the year rather than shearing the clump, and clear everything away in late winter so the new foliage comes up clean. A handful of compost or a general fertiliser in early spring is plenty, since rich feeding only makes it more vigorous. Bait or hand collect snails as the new leaves unfurl.

Choosing a size

This plant is available in 2 sizes, from 140mm up to 200mm, priced from $16.95 to $29.95 per plant. The size shown is the pot the plant arrives in, which is the rootball, not the height of the plant. These are younger plants, priced for planting in quantity, and they establish quickly once in the ground. Not sure which to choose? Read our guide to when to plant in Australia.