Climate zones

Occasionally, I receive e-mails from readers who are confused about which gardening or climate zone they live in. Australia has been divided into as many as eight different gardening zones because of the huge variations in temperature and rainfall across our continent. Altitude variations or geographical features within each zone will modify temperatures and rainfall patterns, breaking up the eight zones even further.
To complicate the issue, climate change is resulting in evolving milder winter conditions in some areas and longer, harsher winters in others. Last summer, extreme heat or rain events played havoc with a lot of gardens across Australia, and the extent of further changes related to extreme weather events is impossible for anyone to accurately predict.
However, Australia can be divided into three basic gardening or growing zones; Warm, Cool, and Temperate (as indicated in the diagram below). The zone divisions are based on the types of plants that will grow in a moderately irrigated garden in each zone
Within these basic zones, altitudes and geographical features gardens at higher altitudes will be cooler than those at sea level in adjoining areas. Sea breezes can provide a milder climate for coastal areas than those a few kilometres inland. Gardens where cold air can flow downwards will be less damaged by frost than gardens in valleys or where solid walls block the escape of cold air. These variations are known as local microclimates, and gardeners may have to make minor adjustments to what they can grow each month according to local conditions, and evolving microclimates brought about by climate change.
New Zealand has a more constant climate and can be divided into temperate and cool zones. Frosts do occur, and snow falls on the mountains, but New Zealand is not subject to hot winds from a parched inland. New Zealand is a very suitable place for growing an extensive range of species from Europe, North America, and the cooler parts of Asia.

These are frost free, or may experience some frosts in inland areas during their short winters, and are not suitable for plants that require a defined period of chilling. Warm zones are suited to warmth-loving Australian natives and plants, including fruits and vegetables, from warmer areas of the world. December, January, and February can be too hot for gardening in a lot of warm zones, and some warm zones experience distinct wet and dry periods requiring conventional vegetables and some annuals to be grown at different times to other zones.
The Tropic of Capricorn runs through the northern states of Australia from Rockhampton and Longreach in Queensland, just above Alice Springs in the Northern Territory, and crosses the West Australia coast between Carnarvon and Exmouth. In areas from Rockhampton northwards, tropical coastal conditions allow an entirely different style of gardening, while in drier areas high temperatures and lower water availability make gardening quite a challenge. Winter temperatures in areas within the Tropic of Capricorn can be higher than summer temperatures in some Cool Zones, and common vegetables from temperate areas can only be grown during winter months. Consequently, I have divided this zone into two sub-sections.
Warm zones:
All of Queensland (except for the southern highlands),
Northern Territory,
North coast of NSW above Coffs Harbour,
Northern West Australia,
Northern South Australia.

These are areas where low temperatures occur for long periods. Frosts are common in winter and can continue into spring. Snow occurs in some areas. Cool zones are suitable areas for growing many European, Asian, and North American plants that require a period of winter chilling. Many of the fruits and vegetables we are familiar with come from cooler climates. They, and frost-hardy Australian natives, grow well in Australian cool zones, but frost-tender plants, and plants which require a long period of warmth to flower or fruit are unsuitable for these areas.
Australian cool zones:
All of Tasmania, and the ACT,
Southernmost part of South Australia including Mt Gambier,
Around Albany in Western Australia,
Most of Victoria (except for Melbourne and Benalla areas),
Far south coast of NSW,
NSW tablelands and highlands.
New Zealand cool zones:
The interior of the North Island,
The entire South Island.
(However, within these areas, protected local microclimates along the coast as far south as Christchurch can be regarded as cool temperate areas, extending the planting range.)

These, strictly speaking, are all areas on earth between the Polar Regions and the Tropics of Cancer and Capricorn. Although winter frosts occur in some temperate zones, soil warms quickly in spring. The areas of Australia not listed above can be considered temperate zones, because an extensive range of Australian and New Zealand natives, and decorative plants, vegetables, and fruits from temperate regions around the world can be grown in these areas. January to late February can be too hot for a lot of gardening activity in some Australian temperate zones, but mild autumn weather usually extends from March through May.
Minimum temperatures within metropolitan areas of Sydney, Adelaide and Perth are similar and tend to be slightly higher than those in surrounding areas. Melbourne’s minimum temperature is only slightly lower, and gardeners in Melbourne may find that they can grow many temperate climate plants in protected gardens.
On the North Island of New Zealand, North and South Auckland areas, Hamilton, most of the west coast to just above Wellington, the Bay of Plenty area, and the east coast to Hastings are temperate zones.

Cabbage white butterfly

These flirtatious little butterflies can be destructive to stressed Brassica plants.
Sowing dill seed between brassicas can deter these pests as the aroma from dill confuses them. If you see these butterflies around your brassica plants, attach the plastic clips from packaged bread to the edges of some of the leaves as a pest deterrent. They look as though pests are already laying eggs on those plants. Use white clips for butterflies, beige for cabbage moth.
If your plants have been attacked, squash any green caterpillars or feed them to the chooks. They often hide along the mid ribs of leaves making them difficult to see. Check daily for newly laid CWB eggs (bright yellow dots – usually on the backs of leaves), and brush them off. Also check for newly hatched larvae – these appear as fine green threads hiding under the leaves, and can look like leaf veins.

White cabbage butterfly or cabbage moth attack is a sign that either:
1) Your plants could do with more water. Brassicas need thorough, regular watering – not a daily sprinkle. Mulching the bed reduces water loss and encourages horizontal movement of water through soil.
2) You have been a bit mean with the complete fertiliser when preparing the bed. Brassicas prefer a humus rich soil to provide a good supply of fertiliser. If they are not making steady growth, a side dressing of compost (under mulch) or applications of complete fertiliser, applied as a tea, can correct the problem. Or, they are missing some essential trace elements that you can supply with a drink or two of good quality seaweed extract tea (such as Acadian, Natrakelp or Seasol).
3) You have added enough fertiliser but the soil is too acid or alkaline for the plants to absorb what they need for pest resistance. If it is a case of too acid – and this can be remedied with an application of dolomite or agricultural lime. If you suspect acidity, apply a handful per square metre of bed and water it in. Avoid using hydrated lime on beds that contain plants as it can burn plant roots. If your soil is too alkaline, the addition of elemental sulphur will reduce alkalinity.
However, if they are making a total mess of your plants, apply Dipel while waiting for soil conditions to improve. Dipel will kill the caterpillars without killing good insects.

Bean Fly

Although bean crops in most areas are close to the end of their productive life (April-May), some gardeners in warm climates are having problems with bean fly.
The best way to avoid bean fly is to have plenty of compost in the bed where you grow your beans so that they will have a full range of nutrients available to them. These pests tend to attack plants that are low in potassium. A drink or two of seaweed extract tea can help bean plants that have been attacked because it has plenty of potassium, as well as trace elements that plants need for good health. But don’t overdo the seaweed as too much can “lock out” some other nutrients.
Also, hill up soil around the main stem of the bean plants to encourage them to send out more roots along the stem above the damaged area just above ground level. Mix some compost through the hilled-up soil. Plants can be saved this way. Also, allow a three year break between growing crops of beans in the same soil.
Bean fly love warm, humid weather. In these conditions put out some yellow sticky paper traps to alert you to their arrival, and hopefully catch some of the adults before they lay eggs. Also look out for fine lines on leaves and stems indicating where the larvae have tunnelled to reach the base of the stem. Stems of affected plants become swollen, cracked and reddish in colour.
Organic sprays are not really effective because the larvae that do the damage are protected by plant cells. A good fertilising and watering routine will help your plants avoid these pests.

Yellow or pale citrus leaves

Autumn is a good time to check your citrus trees for magnesium deficiency. Citrus have a high magnesium requirement and magnesium is essential for the formation of chlorophyll (green colour) in leaves. Without enough magnesium plants will not be able to make sugars and starches, and growth will be poor.
Magnesium deficiency often shows up in citrus in autumn because magnesium is also required for developing fruit and many citrus species produce fruit over the cooler months.
Because magnesium is very mobile in plants, a shortage of this essential element results in magnesium being drawn from the older leaves to new growth. Deficiency shows as pale leaves, beginning with inter-vein yellowing of the outer edges of the oldest leaves, so that a green V remains with the point of the V at the leaf tip, and widest part of the V closest to the stem. In extreme cases, entire leaves may yellow.
Magnesium deficiency can occur in several ways. If soil is too dry roots can’t absorb magnesium, so regular watering of citrus is necessary. It is more common where soil is quite acidic and this can be remedied by watering in some dolomite, which will supply magnesium, plus calcium to raise the pH. If soil pH is in a suitable range for citrus, magnesium deficiency can also occur where heavy rain has leached it from soil, or where excess potassium has been added to soil – this includes use of wood ash, or overuse of seaweed fertilisers, which can cause a build up of potassium.
In these situations, a quick remedy to save this year’s crop is to dissolve some Epsom salts in a small amount of warm water, then dilute it in a full watering can of cold water, and water it into the soil under the outer part of the foliage canopy. You will need about 250 g of Epsom salts for a very young tree, and up to 2 kg for a fully-grown tree.
Magnesium is also important for sweetness of fruit. If your citrus fruits are not as sweet as you would like, it could be due to magnesium deficiency.
However, a general yellowing or paleness of all leaves (chlorosis), while only the veins remain green, could be the result of iron deficiency. Iron deficiency begins in the youngest leaves. This can occur where soil is too alkaline for the tree to absorb iron. If the alkalinity occurred through an accidental overdose of lime or dolomite, the pH can be lowered by adding elemental sulphur to the soil around the tree. If soils are generally alkaline, including some well-rotted cow or horse manure that has NOT had lime added (under mulch, but not dug in) as part of your fertiliser will help reduce the pH by replacing some of the calcium ions in soil with hydrogen ions as it decomposes. To prevent crop losses, it is worthwhile checking soil pH around citrus trees each spring, and correcting it, if necessary.
See also: Feeding citrus