ARID AGRICULTURE. 419 



to send their roots deeply into the soil, where 

 they will not be caught by temporary drouth. 

 During the season the surface cultivation main- 

 tains the soil mulch, saves the moisture, aerates 

 the soil, warms it, fosters the bacteria and chem- 

 ical action which makes plant food available and 

 supplies the small feeding rootlets sent up from 

 below with moisture and food. When the trees 

 are first set out the tops may be trimmed back, 

 but as a rule we would rather take chances on 

 leaving most of the top, at least the terminal 

 bud, as cutting them back often allows them to 

 dry out and they recover slowly or not at all. If 

 the top is to be trimmed back, merely trim the 

 side branches or cut them out, and if any large 

 branch is cut off, paint the wound with white 

 lead. The best time to trim most trees is in 

 spring or early summer. Do not cut off the limbs 

 just before growth starts in the spring, because 

 when the sap comes up, these fresh cuts will 

 bleed and they furnish entrance places for in- 

 sects and fungus diseases. 



WINTER A mulch of three or four inches of barn-yard 



MULCHING * . . , 



manure around each tree during the winter sup- 

 plies plant food, saves moisture and prevents 

 winter thawing of the frozen ground. Do not 

 put such mulch immediately against the trunk 

 of the tree, for it harbors mice, which may gir- 

 dle the tree by eating the bark. Where standing 



