In addition to the intrinsic frost tolerance of a species, a number of factors can affect it either way. On others the way the leaves and young branchlets turned a dark brown was different to what happens when the roots die from wet feet. On many eremophilas and other plants, the split bark - in some cases, shredded seems a better word - was obvious. Some frost tolerant eremophilasĬan I be sure that frost is to blame? The winter was quite dry and well-established plants were killed, which suggest that wet feet did not play a major role. Thus, I estimate that on some nights the temperatures went to -9 to -11 o. I didn't measure temperatures where the plants are, but from readings taken on a thermometer on the house wall under the veranda roof and observing the onset of frosts, I can extrapolate that during "normal" winters the lowest temperatures here would be around -5 or 6 oC, whereas the winter of 2006 provided some temperature readings that were 4-5 degrees below normal. Surprisingly, most verticordias survived with little damage.
In contrast, most Correa, Acacia, Grevillea and Hakea survived, even those less than a year old. All my Lechenaultia, most Eremaea and Beaufortia, and the majority of the banksias died.
Likewise, many established plants of other genera were killed by frost, and the number of deaths was much greater than in previous winters. This time, however, the deaths included a number of plants that had thrived for years, some planted in early 2002. By way of comparison, in the previous four winters (2002 to 2005) I had lost only a few eremophila plants each winter, and invariably those were plants less than a year old I had never lost an established eremophila plant during the previous winters. Many died, and many others were cut back, some quite severely, and in some cases re-shooting started as late as November. This past winter indeed provided quite a test of frost tolerance (though I would have preferred to do without the experience) and sorted the real frost-hardy species from those that are less hardy. Since I had moved here in early 2002, eremophilas had generally done very well for me - until last winter, that is. As some eremophilas took many months to decide whether or not to re-shoot after the big freeze of 2006, I had to wait until I could collate the outcomes. My garden is a good test case for the frost hardiness of plants, perhaps more so than the gardens of most other study group members, I suspect. My garden at Gumeracha in the northern Adelaide Hills experiences lower night temperatures than Adelaide and a number of stiff frost nights even in "normal" winters. Tolerance of Eremophilas to Heavy Frost Hans Griesser
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