Officially, our climate is classified as temperate humid. In winter, the average daytime temperature in July is 10 degrees Celsius, but temperatures can plunge to 4 degrees. The average night time temperature is 3 degrees, but it is not unknown for temperatures to plunge to below zero. These lowest temperatures usually occur for at least a few days most winters. It snows during Ballarat's winters at least every few years, though rarely settles on the ground for any great length of time. Sometimes it does remain overnight, with sufficient coverage to build a snowman!
Coupled with that, clear skies regularly deliver icy frosts, capable of freezing sap in frost tender plants, resulting in frost damage. This appears as burned leaves and blackened branches. Frost can decimate frost tender plants. Last year, during a particularly severe frost, my Tahitian lime was badly frost damaged for the first time in the decade or more it has grown in the backyard. I also lost a number of frost tender succulents for the first time, regetting my failure to move them to more protected positions!
Frost operates a bit like a liquid, collecting at the lowest points as it rolls in across a site. The most naturally sheltered and protected zones occur if there is a building or fence, that will hold some embodied heat, such as bricks, or well positioned trees and shrubs, acting as a shelter belt for more tender plants. It is worth going out into your garden on a frosty morning to see where your frost pockets are located. This will be clear, as it will be the whitest, iciest areas, in the lowest points.
Water too, held in tanks, a pond, or even a swimming pool will also raise temperatures of the area in its vicinity, as water retains heat. This is why seaside locations have a milder climate than those further inland, like Ballarat.
North and west facing positions will always access maximum sun, those facing east are generally more sheltered and shaded from afternoon summer sun, whilst south facing areas of your garden will not only be the most shaded, but also subject to regular blasts of cold wind.
These more protected, or exposed areas of your garden are known as microclimates.
Similarly, a frost pocket is also a microclimate and can be useful for planting species that enjoy winter chill, or are even reliant on it for setting fruit, like cherries. Tulips and many glorious spring bulbs, also thrive on frost.
It is sensible to make the most of these natural microclimates when you are planning your garden or site and plant to give your plants the best possible growing conditions, requiring minimum effort on your part for them to maintain healthy growth.
That said, young plants are often way more prone to frost damage than their established siblings as they adjust to the climatic demands and variations of your site.
It is also worth remembering that Ballarat lags behind Melbourne temperatures and spring always comes at least a couple of weeks later here than in Melbourne. For this reason I do not advocate winter pruning of roses or fruit trees until a couple of weeks into August. This minimises the likelihood of major frost damage and disease attacks, whilst minimum sap flow is occuring in winter dormant plants.
Emergency Frost Protection for your plants.
- Make sure your plants are thoroughly watered during cold weather, as frost will most readily attack already vulnerable plants.
- Cover young or frost tender plants with plastic, or hessian to protect from the frost as it encroaches
- Move frost tender plants in pots indoors, or into sheltered positions under eaves facing east, or handy verandas or even into a shed.
- If a heavy frost is beginning to be evident, go out and hose your most vulnerable plants to prevent the frost from settling on the plant. This will likely involve being outside in the chill of the night and is a last, but useful resort if you are establishing a new garden, or have a few plants that are frost tender and marginal growers within your climatic zone.