What is it like in the humid subtropics for Gardening ?
The climate in the humid subtropics is typified by year round rainfall, the majority of which falls in the summer months, and by temperatures which are less extreme than those found in the southern temperate zone. It stays warmer in winter and is less subject to the heat waves prevalent in the south during summer. This climate zone comes closest to human comfort levels, hence the steady migration north into regions like South East Qld, particularly by retirees.
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Gardening can occur in the subtropics all year round.
One of the most pleasant times to garden, as well as the most productive, is during the winter months, however this is often when southern writers and presenters are telling us to go inside and leave the garden alone!
In comparison, many more people garden in the subtropics and are interested in gardening.
The highest rate of garden visitations in Australia according to the Open Garden Scheme occurs in the subtropics. This area is all the more impressive when you note how isolated many of the Queensland gardens are.
Membership of garden clubs, sales of gardening products, etc indicate that whereas Victoria may think of itself as the ‘Garden State’, gardening is more popular in the ‘Smart State’.
As one moves towards the equator, biodiversity increases at a rapid rate. Ecologists recognise that Queensland has the greatest natural diversity of plants in Australia and most of this is concentrated in the rainforests of the tropical north. Whilst the subtropics does not have the diverse palette available in the tropics, the diversity of plants however can grow is exponentially much larger than that of southern climates.
Unfortunately this wealth is often underutilised as the media focuses attention on those plants that do well in temperate climates, and hence local subtropical gardeners overlook many wonderful plants in preference for plants promoted in media.
Rule of Thumb Principle
As a general ‘rule of thumb’, you could say that plants perform exceptionally well in one climate zone, but tend to grow but not necessarily as well in the adjacent zone. If you want a lush, healthy, low maintenance, pest free garden, it is best to plant those specimens which do well in your zone. Plants that thrive in Sydney or Melbourne seldom do as well in Brisbane; and visa-versa. If a plant is tender and needs coddling in the temperate zone it is likely to thrive in the subtropics.
To get an idea of the ‘best’ plants for a zone, have a look at the predominant plants in local gardens, those that thrive with little care. The neglected (often student rental) houses in the inner city offer the best insight into some of the hardiest garden plants.
For example, the following list are predominant plants for the Brisbane district and gardens:-
Acalypha wilkesiana cvs
Cordyline fruticosa cvs
Codiaeum variegatum cvs
Gardenia augusta cvs
Polyscias guilfoylei cvs
These plants are also dominant in gardens in the areas between Ballina to Rockhampton (the subtropical zone on the east coast).
As the growing season in the subtropics is longer and often continuous, most plants reach maturity faster than those in temperate zones. A garden can look mature in 3 – 5 years. Maintenance however can be a headache if fast growing plants are chosen. It is important that a gardener and professional horticulturist/landscaper focuses on a backbone of slow growing plants.
Whereas frosts are a limiting factor to the choice of plants in the temperate zone, summer rain impacts on many plants in the subtropics. Many temperate zone plants are adapted to a quick growth spell in the favourable spring conditions (temperate zone) of warmth and moisture. They go into dormancy in summer in readiness for drought. However in the subtopics most of these plants either rot or look unpresentable during summer due to the warm and wet conditions.
While roses, camellias and azaleas are grown in Brisbane, it is essential to select specific cultivars for success. Compared to their southern counterparts, these plants often put on a poor show - other shrub species perform a much more outstanding display in the garden. However people will persevere, particularly when these plants have almost novelty status here.
Traditional spring bulbs are generally disappointing here. It may be possible to get one show following planting but that is it (unless growers are prepared to lift and chill your bulbs in the fridge each year). However great success is achieved with summer and autumn bulbs, particularly those from southern and central Africa and central and southern America. Hippeastrums, Habranthus, Zephranthus, Hymenocallis, Crinum, Scadoxus and Eurycles are great performers and put on spectacular shows. Even the local Brisbane lily (Proiphys cunninghamii) should not be overlooked. The autumn planting of bulbs is therefore not as relevant.
People in the neighbouring northern climatic zone, the tropics, know that temperate plants will not grow for them. They know that cultural practices used in temperate climates are inappropriate. However in the subtropics, many temperate plants survive (sometimes briefly!), they may not grow well but they are grown.
People tend to blame the climate instead of realising that their plant choices are inappropriate. This is easily overcome by getting advice or proper understanding of the local situation.
A feature of the natural vegetation in humid subtropical and tropical climates is the appearance of epiphytes on trees where there is adequate rainfall. Historically a significant feature of local gardens is the use of the native staghorn (Platycerium) and birdnest ferns (Asplenium) and orchids mounted on trees. During autumn the magenta flowers of the Cooktown Orchid (our state floral emblem) are spotted moving in the wind among trees in the older suburbs of Brisbane. In spring the scent of Dendrobium speciosum plants high up in the branches are noted.
Keen gardeners utilise exotic orchids, bromeliads and aroids on the trees or walls in their gardens and the garden grows vertically.
People spend more time outside in the subtropics… it is part of the lifestyle.
Gardeners work all year round. The down side to this is that planning and preparation which would normally happen in southern climates during the “down –time” of winter is often neglected. Garden design therefore tends to become more incremental and organic in nature.
Gardens can often look a little faded in the subtropical spring after the dry months of winter. The rain starts to arrive in summer and many plants flower to profusion to ensure the distribution of the next generation in the warm moist soil. This is also an active time for the gardener, an ideal time to propagate plants and plant while the ground is warm and moist.
Autumn is one of the best times for the subtropical garden. The plants have grown over summer, and the temperatures have cooled slightly to make it an extremely pleasant time to enjoy the garden. The light is softer with the haze of humidity overhead. The gardens look lush. It is interesting to note that many gardeners feel the same way and late summer into autumn is the most popular time for subtropical gardens to open in the Australian Open Garden Scheme.
[Extract from article presented at the ABC Gardening Australia Live QLD, April 2003]
copywright is owned by Arno King.
Arno King is a member of AIH, AILA, HMAQ.
for more information, refer to subTropical Gardening magazine ... www.stgmagazine.com.au