Cordyline banksii, The Forest Cabbage Tree

A profile of this little known relative of Cordyline australis
Peter Richardson, Advanced Technologies Ltd., Science Park, Cambridge, U.K.
Chamaerops No. 11, published online 23-09-2002

Above: Wild plants of Cordyline banksii in the Kauaeranga Valley, New Zealand
Below: Cordyline banksii in cultivation in Cambridge (left). On the right is Cordyline australis

I thought I would bring this New Zealand species of cabbage tree to the attention of Chamaerops readers because it seems to be the Ignored Species. Garden centres the length of the U.K. sell C australis, even where it has little hope of surviving outside, and enthusiasts pay inflated sums for plants of C indivisa and C. caspar, but no one pays any attention to C banksii, even in New Zealand.

It has a unique combination of an elegant, 'tropical' appearance with at least equal frost hardiness to the provenances of C. australis commonly grown in the U.K. Its looks ally it with the tropical C. terminals in that the leaves are inserted in just two twisted ranks, opposite and alternate, and are differentiated into a distinct, long petiole and a blade, as opposed to the yucca-like leaf insertion of C. australis, C. indivisa and C. caspar.

It is not a compact plant; on my largest plant growing outdoors in Cambridge the petioles are 40cm long and the blades are up to 120cm long, so the leaves are 1.6m long altogether. This gives the crowns a significantly larger spread than those of C. australis, and they can in fact be a problem to accommodate in a small garden. The petioles have a U-shaped cross section and are held at an acute angle to the stem, and the blades, which have a pronounced midrib, flop out and down gracefully. They have a shiny upper surface. The two ranks of leaves only start to twist after the first year in most individuals, so young plants have a striking, flat, fan-like array of leaves in the manner of the Traveller's Palm, Ravenala madagascariensis. The twist gradually tightens as the trunk grows taller.

The flower panicles of C. banksii are longer and looser than those of C. australis at least a metre long, and arch out and down among the leaves. The flowers are fewer and longer than those of C. australis, and with the same sort of sweet fragrance. In much of the top half of New Zealand's North Island, at least, C. banksii is a rather straggly and sparse little thing, with a few long narrow leaves on a slender stem that quite often leans one way. The upper end of the Kauaeranga Valley at the base of the Coromandel Peninsula has its own, more impressive form however, which has blades up to 10 or 11cm wide. Here, C. australis is exclusively a coastal and lowland species, while C. banksii ranges from the foothills to just below the peaks of the Coromandel Ranges, to 930m. Also unlike the other New Zealand species, C. banksii has a wide light level tolerance, and can be found fully under the shade of Leptospermum trees, or in full sun in waist-high subalpine scrub. A common place to find it is leaning out from steep rocky banks where roads and tracks cut though hilly bush; here all the leaves swing round and hang the same way, out to the sun.

The trunk habit varies drastically with the position the plants are growing in, as well as from genetic influences. The plants in the top photo have single 5m trunks. Some others are multi-stemmed from the base. Some stay unbranched while flowering, but most branch, particularly in full sun. At the highest altitudes on the mountains fringing the Kauaeranga valley they are nearly stemless, resembling the Phormium cookianum they grow in association with there.

It is unlikely that C. banksii from the North Island could survive the worst the British climate can do, but I think it's fair to say if you have grown C. australis successfully, whether planted out or put in a greenhouse or conservatory for the winter, you could grow C. banksii I was reluctant to believe this until this last winter, because it just doesn't look like a hardy plant, but last winter two out of three test plants left outside survived -8¾C. (However, having said that, my experience with all Cordylines in pots is that exposing them to the limits of their cold tolerance in the winter sets them back so they don't start growing again until the middle of the following summer. This coming winter I shall be burying the pots and crowns of my specimens in the greenhouse in polystyrene 'pasta'.) The Forest Cabbage Tree is not fussy in a pot but like most bold foliage plants it looks its best when fed well. It is used to a windy, rainy climate and in warm dry; still air inside it is susceptible to red spider mite.

As I mentioned, the main problem with C. banksii is lack of availability. Burncoose and Southdown Nurseries, Gwennap, near Falmouth is the only nursery I know of that stock plants of C. banksii in the U.K. Graham Hutchins of County Park Nurseries, Wingletye Lane, Hornchurch, Essex, who is a New Zealand plant specialist, has had some of my micro-propagated plants.

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