Shade Tree Suggestions. 13 



The actual date will, .of course, vary according to the altitude. 

 Nursery grown stock transplants more safely than native 

 trees, for reasons given in the paragraph on that subject. 



IRRIGATION. 



Few, if any, of the trees ordinarily used can exist on the 

 plains or table lands without irrigation. Since most of them 

 occur naturally on stream banks, there is little probability that 

 any of them will suffer because of excess of water. On the 

 other hand, it should be said that it is not at all essential that 

 they should be saturated all the time. A good soaking at inter- 

 vals, the length of which will vary according to the character 

 of the soil, will answer just as well. After the trees are well 

 established the intervals may safely be lengthened. 



Toward the end of the growing season, at least a few 

 weeks before the early freezes, the water may well be turned off 

 entirely. This permits the new wood to ripen up, and so it is 

 less liable to be injured by the severe cold snaps that some- 

 times come in September. In late autumn and during the 

 winter it is often well to irrigate at long intervals. In this one 

 should be governed by the needs of the case. Some years of 

 deficient rain and snowfall the soil may become almost wholly 

 dry even in midwinter.* Then it is well to irrigate, for it is 

 certainly true that even in their leafless condition trees lose 

 some water. Evergreen trees, of course, much more, and these 

 especially need some winter irrigation. One can find justifica- 

 tion for such methods in nature. In examining the habitats 

 of our native trees we find that most of them occur on wet, 

 moisture-retaining soils, often where the soils are not only wet, 

 but even flooded. The mountain groves have sprung up on 

 the slopes and in the draws, where the winter snow drifts lie 

 the deepest. 



*See Bulletin 15 of this Station, The Winter-killing of Trees and Shrubs. 



