110 HORTICULTURE, FORESTRY, FLORICULTURE 



trees likewise form hexagons, and when one includes the center tree 

 of each hexagon they form groups of sevens. Hence the name equi- 

 lateral, hexagonal, and septuple. 



The chief advantage of this mode of planting in irrigated dis- 

 tricts is that it provides three and often four different directions in 

 which furrows may be run. Having the choice of so many, it is not 

 difficult to select the one which is best for any particular tract. The 

 ground can likewise be cultivated in more ways and about one-sev- 

 enth more trees can be planted to a given area than is possible in the 

 square method. 



In the past the trees of irrigated orchards have been planted too 

 close. This is made clear to even the casual observer who visits the 

 old orange groves of Riverside, Cal., the deciduous orchards of the 

 Santa Clara Valley, California, or the apple orchards of the Hood 

 River district in Oregon. Under irrigation systems peach trees 

 should be spaced 20 to 22 feet, olive, pear, apricot, and cherry trees 

 from 22 to 28 and 30 feet, orange trees 22 to 24 feet, apple trees 30 

 to 36 feet, and walnut trees from 48 to 56 feet apart. 



On the Pacific coast the tendency toward wide spacing has in- 

 duced many growers to insert peach fillers between other slower ma- 

 turing trees, such as the apple and walnut. 



Methods of Irrigating Orchards. The usual way of irrigating 

 orchards is by means of furrows. These vary in depth, length, and 

 distance apart, but this diversity does not tend to create different 

 kinds of furrow irrigation. The division of this subject is rather 

 due to the means employed in distributing water from the supply 

 ditch to the furrows. In some cases the distribution is effected by 

 making openings in an earthen ditch, in others by inserting wooden 

 or iron spouts in the ditch banks, while in many others flumes hav- 

 ing the desired number of openings or pipes with standpipes divide 

 the supply among the requisite number of furrows. These designs 

 and methods will be described under their respective headings. 



Earthen Head Ditches. Permanent ditches at the head of or- 

 chard tracts should be located by a surveyor. The proper grade de- 

 pends chiefly on the soil. If the soil is loose and easily eroded, a slow 

 velocity is best. On the other hand, the velocity must be sufficiently 

 rapid to prevent the deposition of silt and the growth of water plants. 

 In ordinary soils, a grade of 2 1 /2 inches to 100 feet for a ditch carry- 

 ing 2 cubic feet per second is about right. The amount of water to 

 be carried varies from % to 2 or more cubic feet per second. A ditch 

 having a bottom width of 24 inches, a depth of 6 inches, and sloping 

 sides, ought to carry 1% cubic feet per second on a grade of half an 

 inch to the rod or 3 inches to 100 feet. Such a ditch may be built 

 by first plowing four furrows and then removing the loose earth 

 either with shovels or a narrow scraper. The loose earth may like- 

 wise be thrown up on the sides and top by means of a home-made 

 implement like a scraper. Canvas dams, metal tappoons, or 

 other similar devices are inserted in the head ditch to raise the sur- 

 face of the water opposite that part of the orchard where furrows 

 have been made and which is about to be watered. The chief diffi- 



