FROST HARDINESS TESTING
C.J. Sally Johnson
Frost damage has long been a problem for the conifer nurseryman. Spring can bring red needles, buds that fail to flush, and often 20 percent or more of the crop is lost. What is needed is a method to assess frost hardiness so that crops judged not sufficiently hardy to withstand expected low temperatures can be protected. If frost protection is not possible, then losses can be calculated immediately rather than waiting for spring which may be months away.
There are a number of methods being used by the research community to test for frost hardiness. A good review of these methods has been provided by Timmis (6) and by Ritchey (5). Few of these methods, however, are being used on an operation basis. There are only two methods being used operationally by the forest nursery industry.
The first method is the electrolytic conductivity of water surrounding a tissue sample that has been frozen. This method is being used by the Ontario Ministry of Forests in Ontario, Canada (2). This technique is based upon the principle that freeze injured cells
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