Subtropical rainfall can be very heavy. Large volumes of water can fall in a short time. Subsoil drainage or guttering becomes ineffectual. Water runs over the top of grates and sumps. It is vital that the gardener installs an overland flow path to move excess water and prevent flooding.
Bare ground gets eroded and valuable topsoil is washed away if it is not protected. The heavy rain also leaches the soil of nutrients. These poor and fragile soils require constant applications of organic matter, fertilisers and manures to perform well.
Mulches are indispensable in the subtropics. However the warm temperatures and moisture encourage rapid breakdown. Soft mulches may disappear within 4 weeks after application, so more durable mulches such as barks are needed where lower maintenance regimes are required.
Composting which involves the generation of heat to speed up decomposition is less important in the subtropics than in temperate and cool areas. Garden matter can simply be put back on garden and rots rapidly. Mulching machines are indispensable as garden waste can be aesthetically used straight back on the garden. Compost bins are most valuable for food scraps, to discourage visits by bush turkeys, possums and other vermin.
Plants dry out faster during the warm subtropical days. Moist ground can be dry after two warm or windy days. Potted plants are particularly subject to drying out, and very large pots are the order of the day unless the gardener is prepared to water once or twice daily or install an irrigation system.
Outdoor paving must be non-slip. Moulds and Algae can appear with rapidity during moist weather creating slip prone surfaces.
While cyclones are rare in the subtropics, they do occur and structures need to comply with relevant building codes.
It is important that any trees planted near houses or structures are strongly engineered and not prone to limb drop or shattering during heavy winds. Trees vary in their ability to ride out cyclones. Soils and climate can impact but lists have been developed of trees which are more sound and less likely to drop limbs.
Generally slow growing hard wooded species are the most reliable. Avoid Eucalypts and trees which grow rapidly. These are more likely to cause problems. Palms bend under duress and generally come through well.
While many people are concerned about trees in their gardens, this may be unfounded. It is prudent to consider that the few buildings surviving in Darwin after Cyclone Tracy were protected by surrounding trees.
Make sure that the garden is free from litter or items that can become windblown. These can be more serious than tree limbs during a cyclone.
[Extract from article presented at the ABC Gardening Australia Live QLD, April 2003]
copywrite is owned by Arno King.
Arno King is a member of AIH, AILA, HMAQ.
For more information about gardening in the subtropics, refer to subTropical Gardening magazine - www.stgmagazine.com.au