Today Jan gave me a copy of “The Australian Fruit and Vegetable Garden” book which was published in 2006 by members of The Digger’s Club. This is an excellent publication, and details the types of plants that are suited to various areas of Australia based on different climates. We will use the book as part of planning what vegetables, and fruit and nut trees to grow on Ochre Arch.
From a temperature perspective the book refers to the following ‘growing range of food plants by air temperature’:
* Tropicals CZ 11, 12. Growing range; +5 degrees C to +35 degrees C
* Sub-tropicals CZ 10, 11, 12. Growing range; -1 degrees C to +35 degrees C
* Temperate fruits CZ 8-9a. Growing range; -15 degrees C to +25 degrees C
* Hardy annuals. Growing range; +5 degrees C to +25 degrees C
The book also uses the terms:
* ‘growing days’ which are defined as where the maximum temperature is equal to or greater than 15 degrees C
* ‘hot days’ which are defined as where the maximum temperature is equal to or greater than 30 degrees C
Among other things it is also important to look at minimum winter temperatures.
The above prompted me to figure out what climate zone Ochre Arch fell within, in the context of the various bands that the book discusses. I ended up getting onto the Bureau of Meteorology website to see what data is available, and it just happens that they’ve added an excellent new feature which they’ve titled ‘Climate Data On-line’. To quote directly from the website: “Climatology maps, prepared using data collected over a long period of time (generally 30 or more years), show the variations in climate across the country. Other maps show a range of weather, hydrological and climate information.” In short, one can source average, mean and specific (e.g. minimum and maximum) information for each month of the year since recording commenced by location.
The 3 nearest weather recording locations to Ochre Arch are at:
~ Grenfell (410 metres above sea level, and approximately 20 km [direct] south west of the farm),
~ Forbes (240 metres above sea level, and approximately 35 km [direct] north of the farm) and
~ Quandialla (250 metres above sea level, and about 45 km [direct] south-west of the farm).
The following data was gleaned from the Bureau of Meteorology website:
Long term data – Month by month since Bureau of Meteorology records commenced:
The Bureau’s database records for the long term statistics start from 1965 for both Grenfell and Quandialla, and 1873 for Forbes.
1. Highest ever recorded temperature in degrees C
Grenfell = 43.9 on 15 January 2001, Quandialla = 45 on 31 January 2001, and Forbes = 47.8 on 11 January 1882.
2. Mean number of days (in a year) where the temperature is equal to or greater than 30 degrees C
Grenfell = 66 days, Quandialla = 90, and Forbes = 92
3. Lowest ever recorded temperature in degrees C
Grenfell = -6.5 on 15 June 2006, Quandialla = -5.8 on 21 July 1983, and Forbes = -5.6 on 11 July 1958
4. Mean number of days (in a year) where the temperature is equal to or less that than 0 degrees C
Grenfell = 11.6, Quandialla = 21, and Forbes = 20
5. Mean annual rainfall in mm:
Grenfell = 609, Quandialla = 509, and Forbes = 521
Annual data – past 12 complete months i.e. 1 May 2006 to 30 April 2007
6. Number of days during the period where the temperature is equal to or greater than 15 degrees C
Grenfell = 313, Quandialla = 331, and Forbes = 329
7. Number of days during the period where the temperature is equal to or greater than 15 degrees C (See point 6 above) LESS Mean number of days (in a year) where the temperature is equal to or greater than 30 degrees C (from point 2, above):
Grenfell = 247, Quandialla = 241, and Forbes = 237
The figures show some (to me) significant differences, especially between Grenfell and the two other towns of Quandialla and Forbes.
Quandialla and Forbes have almost twice as many frost nights (where the temperature is equal to or below zero) each year than Grenfell. Grenfell’s higher altitude (410 metres V 240 & 250) could be one of the key factors, as could the fact that the location of the Grenfell weather station is on the top of the main hill in the town whilst (the topography of) Forbes and Quandialla are quite flat. Cold air is heavier, so the temperature on the top of hills is as a rule warmer than in the gullies. Curious that Grenfell has actually recorded a lower minimum temperature than Forbes and Quandialla (and that is occurred only last year), presumably due to the higher altitude?
Quandialla and Forbes both have almost 50 % more hotter days (greater than 30 degrees C) than Grenfell. My theory is that altitude has the biggest impact. Forbes and Quandialla have both recorded higher maximum temperatures than Grenfell. It’s also interesting to note how hot it was at Forbes in 1882 (and a pity I don’t have comparable data for the same year for Quandialla and Grenfell).
I’m not sure whether it is valid to do the calculation I’ve done in point 7 above (deducting ‘hot’ days from ‘growing’ days to in effect come up with a ‘net annual growing days' number), but if it is then the result effectively means that all 3 locations have about the same number of net growing days. Grenfell is renowned as one of the best dryland cropping regions in Australia. The above statistics would suggest that this is driven by comparative altitude (less hot days to knock the crops around), comparable growing days and higher mean annual rainfall.
Ochre Arch’s altitude varies from around 315 metres to 415 metres above sea level. This provides us with some excellent opportunities to site different species of fruit & nut, and vegetables to suit their natural requirements. For example, we’d place plants needing more frost on the lower areas near the gullies; and those plants that do not like frost toward or on top of the hills. From a ‘human habitation’ angle it would seem that given the house is on the lowest part of the property it will be subjected to the coldest nights and hottest daily temperatures. Perhaps we need to relocate it to the hills! It’s also my gut-feeling that the amount of rain that falls on our higher country is higher than on the lower. In time I hope to prove or disprove this as we now take rainfall measurements at both the house and near one of the high points on the property.
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