350 SEEDING AND PLANTING 



spring when the soil is cold and the roots unable to supply the 

 transpiration losses. It is most liable to occur on heavy, cold, 

 overwet soils and can be prevented by shading the beds in early 

 spring. 



Frost damage is due to the formation of ice crystals in un- 

 ripened tissues while the vital processes are still active in the 

 cells. It is usually confined to the part of the plant above ground 

 although the early autumn freezing of the soil may injure growing 

 roots. When seedbeds are sown in late spring or early summer 

 the resulting plants are later in maturing their wood and they are 

 likely to be severely injured by early autumn frosts. When seed- 

 beds are sown in the autumn and the seeding is followed by a 

 period of warm weather, germination takes place and the seedlings 

 are destroyed or severely injured by freezing. In the latter case 

 mulching or shading will not protect the young plants from injury. 

 The damage can be avoided by delaying the seeding until all danger 

 of autumn germination is past. Species like white pine, jack pine, 

 and Douglas fir that start their growth early are often severely 

 injured by late spring frosts. The terminal buds and young shoots 

 are destroyed if severe frosts occur after growth begins. The 

 simplest method to prevent injury in localities where late frosts 

 are likely to occur is the holding back of early growth by shading 

 the beds. When there is likelihood of a killing frost during the 

 growing season the beds can be protected by covering them with 

 hay, straw, or other light material. Where there is an abundant 

 water supply and the slope of the ground permits, frost damage 

 can be prevented by flooding. 



The excessive use of water during the early growing season, 

 particularly on heavy soil, often causes the roots to rot and the 

 tops of coniferous stock to turn yellow. After the damage appears, 

 the stock seldom recovers but quickly turns brown and dies. 

 This loss which is often excessive can be entirely avoided by the 

 proper regulation of the water supply. It seldom occurs except 

 in nurseries under irrigation. 



5. Protecting the Nursery from Injury by Birds. Birds are 

 seldom harmful in the forest nursery until germination takes place. 

 They seldom dig up the seed if it is well covered. Many species 

 are highly beneficial due to the harmful insects that they destroy. 

 They are chiefly destructive to conifers and small-seeded, broad- 

 leaved species that raise the seeds above the ground as they germi- 



