The difference between 2013 and 2014 peach harvests has been inexplicable; from boom to bust with a vengeance. With five peach trees on the property, we’ve had not a single peach reach the kitchen. What’s gone wrong?
Some peach trees fall into a boom and bust rhythm, especially if allowed to crop too heavily in any particular year - they respond by boosting vegetative growth in the following year. But that would not explain total failure among both early and late varieties that are naturally out-of-sequence with each other.
The clue came a few weeks ago in a public talk at the Rare Fruit Society by Graham Brookman from the Food Forest; the winter of 2013 was much warmer than the long-term average and the peach trees had not clocked up their requisite ‘chill hours’. I hadn’t registered that myself, as we’d been off on the annual pilgrimage to Germany last July, enjoying the northern summer while the garden should have been shivering its way through the coldest month of our year. I did come home to experience Australia’s warmest September on record.
So what are ‘chill hours’, and what will a lack of them mean in a warming climate?
Peach trees are deciduous and so build their buds during summer before dropping their leaves to over-winter. These buds will develop either into fruit or leaf clusters during the following Spring but face the risk of breaking dormancy during a warm spell in winter, only to be ‘burnt off’ by a following frost. So to protect their buds against freezing winter temperatures and this danger of waking up too soon, stone fruit have developed ‘clocks’ that must ‘tick off’ a certain number of chill hours between 0⁰C and 7⁰C (32F and 45F) during the winter months. In the case of our peach varieties, we need around 500 chill hours for proper leafing and fruiting; Graham stated that we had fallen well short of this in the winter of 2013.
One’s local climate sets what fruit trees will and won’t work. Here on the Adelaide plains, it’s hit-and-miss to grow apples, cherries, kiwifruit and other high-chill varieties. Stone fruit such as apricots, nectarines and peaches are usually solid performers unless we experience an unusually warm winter, as we did last year. Shifting to ‘low chill’ varieties is a long-term strategy; solid advice from a local nurseryman is advisable before finding space for fruit trees in a backyard garden.