Research on Hedging and Coppicing
In early September I attended two lectures put on by the Friends of the Royal Botanic Garden, Cranbourne. These were on the results of research carried out by university botanists on aspects of cultivation of Australian plants. It's great to see this type of research finally taking place.
Hedges serve different roles in design, screening areas of the garden and providing sheltered microclimates. Dave Kendal spoke about his trials of hedging with fifteen different species, all but one of them Australian plants. For his research he planted 40 hedges each of 5 plants spaced at 300mm centres. They were first pruned 6 weeks after planting and the study is now 3 years old.
The requirements Dave was looking for in hedging plants were:
- ability to tolerate severe pruning;
- retention of basal foliage;
- high shoot density;
- relatively small leaves;
- quick formation then slow growth;
- freedom from serious pest and disease problems;
- genetic uniformity (though he questioned whether this was always essential).
He assessed the hedges himself and also visited many groups of people (for example, APS groups) with photographs of his hedges, asking which ones people preferred in terms of their appearance. Dave provided a very helpful summary of his results, from which the following extracts are made:
Of the 15 species he tested (one an exotic, some indigenous to Melbourne (i), some requiring irrigation (ir ), his 7 Australian recommendations were:
Four species not recommended but still worth considering were:
- Formal hedge (2-3 trims per year): Philotheca myoporoides (ir), Westringia fruiticosa, Correa alba (i)
- Informal hedges ( 1-2 trims per year): Callistemon "Captain Cook", Dodonaea viscosa (i), Rhagodia parabolica (i)
- Tall screen (1 trim per year): Bursaria spinosa (i)
- Acacia acinacea: Dave said "I really liked it, but it has an unusual branching pattern that not everyone liked. Flowered profusely." (I liked it too.)
- Kunzea ericoides (Burgan): "not appealing after trimming, much more attractive left unpruned"
- Acmena "Minipilly": "attractive immediately after pruning, regrew very unevenly"
- Eremophila racemosa: "popular but fragile and likely to be short-lived"
Three species were dropped from the study, two because of too many plant deaths (possibly due to high levels of fertiliser) and one because the form selected was too prostrate. Dave said the species he tested were certainly not the only Australian plants worth testing.
From the introduction to the Friends of Cranbourne lecture.... "John Raynor's teaching and research interests include design, planning and managing landscape vegetation, particularly low-water use perennials, groundcovers, shrubs and climbers. He has established a number of research plots to assess the growth and forms of many Australian shrubs and groundcovers, including Atriplex, Correa, Dianella and Rhagodia species. In recent years John has been completing research into selected Eucalyptus species for use as 'low-input, managed forms' in urban landscapes."
This research reflects a new approach to the use of Australian plants in urban landscapes. As with hedging, it could help introduce their wider use by making possible more automated or, at least, automatic and regular maintenance over time. Altogether John investigated the coppicing of 20 different eucalypt species. These were grown as replicates in blocks of 4, spaced at 50 cm, trimmed to a height of height of 1 - 2 metres.
Some eucalypt species were rejected as being:
- too vigorous: E. bridgesiana, cephalocarpa; dalrympleana; rubida.
- not vigorous enough: E. albida; crucis; cyanophylla; gillii.
The most promising species were: E. cinerea; perinniana; polyanthemos; pulverulenta .
John found the best of all was E. pulverulenta (used by Paul Thompson in Birramung Marr, near Federation Square in Melbourne), in particular the form E. pulverulenta "Baby Blue".
Other eucalypts mentioned in John's talk were:
- E. gunnii unsuitable because it has no lignotuber;
- E. crenulata unsuitable because its basal shoots are too large;
- E. saxatilis used for a hedge in Burnley;
- E. nitens used for hedges in the U.K.; .
- E. cinerea is used for hedges in New Zealand and Chicago.
From the newsletter of ASGAP's Garden Design Study Group, November 2007 issue.
Australian Plants online - 2007
Association of Societies for Growing Australian Plants