Autumn is in full swing, the leaves are falling, the days are sunny and the mornings are getting crispy. The frost season has started in our cool climate region of the Southern Tablelands. This is not uncommon for this part of the state known as the Capital region. The Capital region, the Alpine regions of NSW and Victoria and many parts of Tasmania are the most extreme cool climate regions in Australia. Apart from the Alpine regions which experience heavy winter snow falls, the Capital region (and Tasmania) is the harshest frost region in Australia. We experience on average 109 frost nights per year. Our frost season officially begins on 23 March through to 22 November, although we can have a frost outside of this time frame. While this high number of frosty nights can mean some very cold starts to the day it also means we have an equal amount of bright sunny joyous days.
While Braidwood experiences a long frost season we rarely experience snow.
Other frost prone cool climate regions of regions of Australia experience between on average 20 to 50 frost nights per year with an average minimum temperature of 0 ° (The Central Tablelands, Central West, Northern Tablelands and some parts of the Darling Downs). In the Capital region our average minimum temperature is -5 °. This is why we find that most cool season planting guides do not seem "right" in our region. Cool season planting guides are based on climate conditions of the more "moderate" cool climate areas, which form the majority of cool climate regions in Australia.
Frosts and low temperatures can have a detrimental affect on plant growth and development, however there are some plants that require a period of cold to be fully productive. Garlic is one such plant. The Turban varieties (Monaro Purple) are generally planted in Autumn (April) with early pre winter growth focused on root development. Growth continues through winter and it is the increasing day length and warming soil that stimulates bulb development in early spring. Other cool season vegetables include members of the Brassica Family - cauliflower, broccoli, cabbage, brussel sprouts, kale to name a few. However there are some traps for the unwary with some members of this cool season plant group. Our very low temperatures (average minimum -5 °) while not having an impact on plant growth, will burn the developing heads of both broccoli and cauliflower. This is when you need crop protection. It can be as simple as a plastic plant pot placed over the forming head each night to provide protection or for a larger number of plants, agricultural fabrics can used to cover entire rows.
At Wynlen House we use agricultural fabrics with a metal cloche frame to provide crop protection. The material we mostly use is a knitted permeable plastic polymer (polypropylene) called insulnet. Thermal Fleece is another product and these permeable textiles allow water to pass through and the plants and soil can breathe. Shade cloth can also be used to provide reasonable crop protection. Agricultural fabrics limit light frosts but do not provide complete protection particular from hard frosts. More importantly, they ameliorate the overall impact of very low temperatures enabling plant growth and development to continue, maintaining soil temperatures and air temperatures up to 3 ° warmer than unprotected garden sections.
The use of row covers or even very simple low cost plant protection strategies enables all year vegetable production in the low temperature extremes of our cool climate region.
Insulnet is available from Redpath Australia http://www.redpath.com.au/
Thermal fleece is available from Weed Gunnel http://www.weedgunnel.com.au/
Bronwyn Richards has cared for animals and has been growing vegetables successfully all her adult life. She is principle gardener for Wynlen House Farm