Use of water in the garden - establishing a three bucket rainforest.
Colleen Keena, Qld
Australian droughts can be both severe and extended. For those outside town limits, tanks run dry and farm dams empty. For those with access to reticulated water, the installation of water meters has heightened awareness of the cost associated with water use, particularly as it has been emphasised that much of the water currently being treated to the standard required for domestic consumption ends up being either flushed away or poured onto gardens.
While no-one wishes to see another extended drought, the last four years have forced a new understanding upon those who have experienced the prolonged dry Period: the availability of water cannot be guaranteed and treated water comes at a price. This has already started to impact upon gardening with a recent book as well as articles in garden magazines noting ways to design water-efficient gardens. Australian species have been included but no publication that I have seen has been devoted exclusively to the use of local species.
The re-examination of the use of water in the garden has coincided with an awareness of the advantages of locally occurring species as well as with an enhanced interest in rainforest species. A request for assistance with designing a "rainforest" that would receive only natural rainfall gave impetus to applying knowledge that had been slowly increasing over the last decade.
This article has as its focus the learning that has enabled the establishment of a flourishing rainforest garden under severe drought and extreme weather conditions. No attempt has been made to describe the design concept in detail.
This was the first concept to be incorporated in the no-water rainforest. Experience with mounding and channeling suggested that, although this is a necessary component of a water-efficient garden, something further appeared to be required. More recent publications include a discussion of the advantages of Some sites, e.g. steep creek banks, are unsuitable but where deep-ripping is possible, plants benefit deep-ripping from the release of soil nitrogen which occurs and assists in establishing seedlings. As well, finely cultivated soil improves both the growth rate and the survival rate as it allows the plant to produce the maximum number of feeder roots.
Soil preparation, including deep-ripping, therefore appeared to be the second important element of a no water design especially as rainforest species do not have the aggressive root systems of the open forest plants and have an unsatisfactory survival rate if the root system is not adequate to sustain the plant after planting. The third vital component appeared to be the inclusion of species from dry rainforests, locally occurring if possible as local native plants will be most likely to handle local climatic extremes.
There is a wide range occurring in the local area. Some of these local species have been used extensively as street trees in Brisbane, e.g. Brachychiton acerifolius and Harpullia pendula. Other local dry rainforest species have been widely cultivated and survived the current drought, e.g. Brachychiton discolor; Flindersia australis, Grevi1lea robusta, Hymenosporum flavum, Melia azedarach var australasica, Pittosporum rombifolium, Syzygium australe. Others can be seen growing locally, e.g. Ficus fraseri, Glochidion ferdinandi, Hibiscus heterophyllus and H splendens. Sometimes plants from the same family as local species were chosen for inclusion, e.g. Brachychiton bidwilli, Grevillea hilliana and Syzygium oleosum. The planting was predominantly of local species, though species not known to occur locally were also included, e.g. Buckinghamia celsissima as it is reliable as a street tree locally and is a favourite of the owner of the garden.
The 1986 publication of John Hunt's book 'Creating An Australian Garden' described the advantages of mounding and channelling. Some of these are artificial watering is not required except in times of extreme drought; soil temperature remains cooler due to increased moisture level; plants will flourish and last longer than plants grown with more artificial watering.
CSIRO report - Acacia