144 THE CULTIVATED EVERGREENS 



Mulch injury. 



When close, heavy mulches are used, the tops of seedlings 

 may die in winter while the mulch is still on or just after it 

 is removed. The roots, however, do not die until some time 

 after the tops. The immediate cause of death is at present 

 unknown, but it may be prevented by care in supplying a 

 mulch which is neither too heavy nor too compact. 



2. Diseases and injuries of older coniferous trees 

 Winter-killing. 



This type of injury has been described as it occurs in the 

 nursery. Older trees are also subject to it, especially in mild 

 winters when there is very little snow covering and in the 

 early spring. Owing to the fact that conifers retain their 

 leaves during the winter and, therefore, transpire more freely 

 at the critical periods than do deciduous trees, they are par- 

 ticularly susceptible. The symptoms are as previously de- 

 scribed. The needles die from their tips and finally become a 

 reddish-brown color. Many terminal buds are often killed 

 and whole trees are sometimes defoliated. Certain junipers, 

 especially Juniperus virginiana and J. chinensis, are very cap- 

 able of withstanding such conditions. 



The injury is most likely to occur when ornamental trees 

 with a shallow root system are situated in exposed positions. 

 Mulching should afford satisfactory control. 



Frost-injury to roots. 



In very severe winters when there is but little snow, the 

 roots of trees may be partially or entirely killed. This is very 

 likely to occur in the case of trees which possess shallow root 

 systems, such as European larch, pines, and hemlock. It is 

 frequent in white pines. If all the roots are killed, the tree 



