NURSERY PRACTICE FOR PRAIRIE-PLAINS PLANTING 131 



because of their larger leaves and more rapid growth, will as quickly 

 afford mutual protection as the overdense stands of 30 to 40 seedlings 

 per foot. 



Foliage appears to give the most protection to the stems of the 

 plants from the direct rays of the sun if the rows are in line with the 

 sun in midafternoon, when temperatures are highest. In a few 

 nurseries it has been observed that heat injury was reduced if the 

 rows ran in a north-to-south or northeast-to-southwest direction. 

 Slope of the land will govern row direction, however, wherever furrow 

 irrigation is practiced. Even where overhead irrigation is used, the 

 row direction will probably be influenced more by the direction of 

 prevailing wind during the growing season than by the possibility of 

 heat injury. 



Drought 



Injury from drought occurs in nurseries when the soil moisture is 

 depleted to such an extent that the moisture cannot be absorbed by 

 the roots of the seedlings at the rate required to offset the moisture 

 lost by transpiration. This results in wilting and if prolonged will 

 cause the death of the seedlings. High temperatures, low humidity, 

 wind, and intense solar radiation will increase the rate of transpiration 

 and will intensify the injury caused by low soil-moisture content. 



When adequate natural rainfall does not occur, restoration of soil 

 moisture by irrigation is an absolute necessity to prevent serious 

 drought injury. An adequate irrigation system is an indispensable part 

 of the physical equipment of any nursery located in areas where peri- 

 odic droughts occur. 



Frosts 



Killing frosts in late spring or early fall are of relatively common 

 occurrence in the plains region. Proper nursery practices, such as 

 delaying spring sowing until danger of frost injury to germinating 

 seedlings is past, are the best safeguard against normal frosts. Xo 

 wholly practical safeguard exists against the occasional severe late 

 spring or early fall frosts. 



If a sprinkling system is available, it should be turned on during 

 cold nights to reduce or prevent damage. This is the most feasible 

 protective measure that can be suggested for nurseries equipped with 

 overhead irrigation. 



Smudge pots, such as are used in California orchards to create an 

 insulating blanket of smoke, may possibly have some effect on the 

 prairie plains, if topography and air conditions are favorable. They 

 have not been tried to date. 



Mulching or covering the seedlings with straw will prevent injury 

 from late spring frosts where stock is grown on a small scale in beds, 

 but it is not practical for large nursery operations. 



Tops of seedlings may suffer severe killing-back by frosts but. unless 

 the root crown is injured, such seedlings will sprout from the root collar 

 the next spring and establish new stems. Thus it can be said that the 

 root crown or collar (for species which do not sucker from the roots) 

 is the heart of the seedling. When it is dead the seedling is dead, 

 regardless of the condition of the other parts. Covering the young 

 seedlings with soil for 24 to 48 hours will ordinarily not prove harmful, 

 and where warning is given soon enough this may greatly lessen the 



