342 MAINE AGRICULTURAL EXPERIMENT STATION. I9IO. 



the low temperatures are experienced is also a contributing fac- 

 tor. The more water they contain, beyond certain limits, the 

 more likely will they be injured by freezing. This probably 

 accounts for the fact that very frequently in Maine the trees in 

 the more exposed locations have suffered less from winter kill- 

 ing than those in more sheltered situations. There was better 

 drainage, the ground frozen more deeply and the roots chilled 

 and inactive and not supplying water to the plant tissues above. 



The severe winter killing of 1906-7 was probably due to the 

 combined influence of low temperatures alternating with high 

 and a large percentage of water in the tissues of the trees. 

 Weather conditions of January, 1907, were particularly favor- 

 able to this as will be seen by examination of Fig. 237 which 

 shows within a week a record of — 40° F. and — 35° F. with 

 two warm days having a maximum temperature of -|-45° F. 

 and +47° F. situated midway between. Moreover it will be 

 seen that the changes from extreme cold to thawing and back 

 to cold again were quite abrupt, particularly in the case of the 

 latter. Winter killing of trees may occur, however, as the 

 result of a deficiency of moisture in the soil associated with 

 continued cold, dry winds in winter. 



Much of the danger from winter killing can be avoided by 

 planting only those varieties which have been found to be per- 

 fectly hardy in a given locality. Only the most hardy varieties 

 should be planted in those parts of the State where the mini- 

 mum winter temperature frequently reaches or approximately 

 reaches — 30° F. The planting of Baldwins and possibly Ben 

 Davis as large commercial ventures should be restricted to those 

 parts of the State where the minimum winter temperature, re- 

 peated at frequent intervals, seldom reaches below — 20° F. or 

 at the utmost — 25° F. The location of, the orchard may have 

 much to do with hardiness. Low, heavy or wet soils should 

 be avoided, — it was orchards in such locations which suffered 

 most in the severe winter killing of 1906-7. Those which were 

 located on more or less sloping land with good air drainage, 

 with plenty of natural or artificial soil drainage as a rule suf- 

 fered much less from winter injury. 



There is considerable difference of opinion among Maine 

 orchardists with regard to the value of wind-breaks. A very 

 good illustration of the good they may do was furnished by an 

 Orono orchard following the severe winter just referred to. 



