About This Report ... 



Cold damage is a major limiting factor in the successful production of fruits and nuts. 

 In large measure, the northerly limits for economic production of the various crops are de- 

 termined by their inherent ability to tolerate extreme cold or sudden drops in temperature. 

 Even where production of a particular fruit or nut is established, cold damage is a hazard 

 that varies with the kind of crop and the climate. Every year individual farmers suffer light 

 to heavy losses due to cold damage. And in infrequent years of major freezes, whole areas 

 are hard hit. 



Scientists have long been searching for hardier fruits and nuts. Steady progress has been 

 made through systematic exploration, breeding, and evaluation of potentially useful plants. 

 Many promising varieties have been introduced and some of them are widely used for fruit- 

 ing or as hardy rootstock or interstock. As a result, present-day farmers in some instances are 

 better able to protect themselves against cold damage. But despite progress, cold damage con- 

 tinues to be a problem that varies in kind and degree with the crop and environmental con- 

 ditions under which it is grown. Fortunately, new research techniques are continually being 

 developed to hasten the development of hardy varieties having other desired traits. For ex- 

 ample, monoembryonic seed parents are being used to accelerate the production and testing 

 of citrus hybrids. And new methods for objectively rating the hardiness of experimental plants 

 in advance of fruiting will expedite the evaluation of crops that are slow in coming into 

 production. 



Many factors affect cold hardiness. This complicates the search for plants that will sur- 

 vive adverse winter conditions. Characteristics that promote hardiness under one combination 

 of circumstances may make a plant more susceptible to cold under another set of circum- 

 stances. To be truly hardy in many areas of the Great Plains, for example, a plant must bt 

 able to tolerate dessicating winter winds as well as extreme cold. And plants that tend to 

 bloom early — such as apricots, almonds, and tung — can be expected to succeed only in areas 

 with mild winter and spring temperatures. Consequently plant explorers and breeders search 

 for plants that are adapted to growing under widely varying conditions or are adapted to the 

 particular area in which they will be planted. And farmers in the market for hardy fruit and 

 nut stock need to make sure that they obtain trees adapted to the climate of their particular 

 area. 



This report brings together information from various sources on cold hardiness research, 

 particularly information regarding cold hardy varieties of fruits and nuts introduced or devel- 

 oped by the Department of Agriculture working independently or in cooperation with the 

 various States. Its purpose is to provide agricultural agents and other educational leaders 

 with up-to-date background information for answering general questions about this broad 

 subject. 



Information for this report was provided by the Crops Research Division, Agricultural Research Service. 



