by Ken Russell

Although there are almost 50 species in .the genus Cymbidium, only three are native to Australia – Cymbidium canaliculatum, C. madidum and C. suave. These three species occur only in Australia. I have made an extensive study of these species where they grow in nature in New South Wales and southern

Queensland and have discovered surprising differences in their cultural likes and dislikes, particularly the pH of the decayed material surrounding their roots. These results provide useful clues as to how we can better grow these three Aussies in cultivation.

I have examined plants of C. canaliculatum between my home town of Dungog (NSW) and Roma in Queensland, a habitat range of 1400 Km. Daily temperatures in its various habitats range from -12 degrees C to +50 degrees C. Plants were found on a variety of hosts – eucalypts, native pines and native oaks – both living trees and stumps or fallen logs. Of the total plants surveyed, 60 were found on living trees and 85 on stumps or fallen logs. Ten were found on live native pines while thirty grew on fallen pine logs. pH tests were made around the root systems of each plant, both near the surface and well down around the lower root System. The pH near the surface differed markedly from lower down, as shown by the following values:

Host                          pH (near surface)              pH (lower down )

Live pines                    6.0                                      9.0
Pine logs on ground     6.5                                       9.0
Other live trees            7.0                                       9.5
Other stumps & logs    7.5                                       9.5

The pH measured near the roots of seedlings (average leaf length 150-250 mm) growing on live native pines was only 4.5 but measurements taken on older plants ranged from pH 7 to 9. It seems therefore that the root system of Cymbidium canaliculatum prefers alkaline conditions, preferably about pH 9, and may modify its environment to suit. I recommend spraying cultivated plants with lime spray (1 gm per L) four times each year. This species grows vigorously in spring and summer and benefits from fertiliser applications during this period. In nature the root system hardly ever becomes dry, as the channel-like leaves channel any moisture provided by rain, dew or frost to the base of the plant. Decayed leaf matter provides the main source of nutriment.

Cymbidium suave plants were studied in nature between the Hunter River (near Newcastle, NSW) and the Brisbane River (near Ipswich, Queensland), a range of 1000 Km. Some plants were found near sea level (25 m), others at elevations up to 700 m. Hosts included blue gum, spotted gum, grey gum, water gum, red gum, brush box, blackbutt, stringy bark, ironbark, tallow wood, native pine and oak. Again, pH measurements were made just under the leaf mould at the base of the plant and also much further down in the rotted heartwood (mudgut).

Number Host                  pH (near surface)     pH (in mudgut)

195 dead stumps               4-5                        4
65 dead wood logs             4.5                        4
15 live trees                       4.5                        4
8 on rocks/bark                 5                           4
5 sick plants in stumps     5                            6

Obviously, the root system of this species prefers acidic conditions. The study covered 288 plants in all, 250 of them carrying seed capsules (it was late September). The best plants had a 25 mm layer of good leaf mould from decaying leaves, twigs and bark around their bases. Decayed material (mudgut) taken from the centre of host stumps have pH 3.5- 4, and I recommend the use of this material to achieve a Satisfactory pH range when cultivating Cymbidium suave. Other materials suitable for adjusting the pH of the potting mix include Phostrogen Acid Plant Food (a new product with pH 4.5), pineapple juice (pH 4.5) and cofee grounds (ph 4.5). Never apply lime to this species, as it hates alkaline conditions.

Only eight plants of Cymbidium madidum were Studied, all of them living on trees, logs and stumps in the Coifs Harbour area (mid-north coast of NSW). Material surrounding their roots had pH 6- 6.5.         KR

From ANOS Warringah Group Inc.  newsletter of September 2019  (Website)