Australian Proteaceae in Pots

Graeme O'Neill

Any person who grows Western Australian Proteaceae species in the open garden in Canberra expects to suffer pain, and is usually not disappointed. I have, indeed, been richly rewarded with pain in the past three years.

In fact, I have been able to add an extra dimension to the basic, economy size pain pack by choosing to domicile myself in the frost-blasted, phytophthora-ridden swamp of Macgregor* depths (the denizens of Macgregor heights, having chilled their winter air, send it coursing downhill to us. On midwinter mornings, the silence is broken only by the sound of magpies falling off the clothesline and shattering on the ground).

This brief article serves to introduce the subject of growing Proteaceae in pots, for the preservation of one's sanity.

The system is very simple. Mix two parts of coarse, washed sand with one part Australian peat moss and one part perlite. Plant your plant. Water once a month with halt strength Aquasol. Wait. Fall on ground in ecstasy at first sign of bud.

The system is foolproof, but one can strike a blow for idiocy by leaving prize specimens in black pots to the mercy of midsummer sun, which generates root temperatures high enough to kill a clinical thermometer. Plants survive if they have enough water, but roots at the edge of the pot die and set back growth several months, and terminal growth dies back.

The system is essentially hydroponic, although the sand contains some nutrients. Aquasol, a low-phosphate liquid fertiliser, seems to provide for the plants' needs, and I use a once-a-year sprinkling of trace elements.

Banksia gardneri is one of several Western Australian species with a prostrate habit of growth. Select the thumbnail image or plant name for a higher resolution image (39k).

There is no possibility of overwatering, and excess nutrients are simply leached out through this very porous mixture. Provided seedlings have been raised in the same mix, and not purchased in normal potting mix, there is no danger of phytophthora.

The pH of the mix is about 6.5, ideally suited to most species of Proteaceae. The perlite and peat moss hold plenty of water, although watering must be done every two days in summer when the plants get large.

I grow my larger WA banksias in large "Hostess" pots (45cm dia) which are cripplingly expensive. The coloured ones do not overheat as much but they do crack in about three years (usually not beyond recall, just superficial), whereas black ones do not, and are slightly cheaper. Small species are grown in smaller "Hostess" pots (32cm) or in 25cm or 20cm black nursery pots.

Growth rates are excellent, and for larger plants, pruning to prevent legginess is essential. For example, Banksia ashbyi has grown from 60cm to 120cm in a season, after removal of two prunings of 10cm to promote branching. Like B.coccinea, it is wilfully apically dominant, and is slow to respond to secateur discipline.

I have flowered three species so far - B.burdettii (which set four magnificent orange and white flowers from an initial bud count of 15, curse the bug which bores into stem apices!), B.baxteri, with two flowers, and B. sp.aff.repens (Lake King).

In bud in smaller pots I have B.violacea and one of the B.sphaerocarpa group, the first two years old, the other three.

Other Banksias in pots are: B.brownii, B.candolleana, B.solandri (superb foliage, suspicious bracts present but no buds), B.hookerana (ditto), B.praemorsa, B.elderana, B.lindleyana, B.laricina, B.meisneri (a delightful, delicate species in foliage, great potential as a pot specimen), B.pulchella, B.tricuspis, B.victoriae, B.goodii (prostrate), B.gardneri (ditto) and B.petiolaris (ditto), plus another four forms of the B.sphaerocarpa group which may soon be accorded species status**.

Isopogon trilobus is a spectacular Western Australian species which is a difficult garden subject in humid districts. The pink/mauve flowers are seen in spring. Select the thumbnail image or plant name for a higher resolution image (32k).

I also have about 25 Dryandra species making good progress in 20cm pots, four Isopogon spp, Petrophile linearis, Synaphea petiolaris, and sundry non-Proteaceae species.

One of the advantages of larger pots is that one can plant other species in with the banksias as an 'understorey'. I have been using mainly lechenaultias for this purpose - L.biloba, L.floribunda, L.formosa, L.laricina and L.tubiflora are all thriving, with an odd Hibbertia stellaris, a Dampiera purpurea and Diplolaena angustifolia (Rutaceae) plus the eastern species Wahlenbergia gloriosa and W.ceracea.

It's cheating, of course, something like running under the hurdles in a steeplechase. One can even move the pots out of the frost.

Cheating results in vigorous, magnificently healthy plants with wonderful flowers. When the precious species die in the garden, one can weep crocodile tears into the container of surviving sibling, without fear of inducing salinity.

Australian Plants online - March 1997
The Society for Growing Australian Plants