This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
In order to provide a mulch, thus checking evaporation and also to kill the weeds, cultivation should be conducted in the new plantation as long as possible without danger of injuring the young trees by driving a horse between them. The plantings generally may be cultivated for the first season and part of the second before the limbs of the trees spread out and interlap so that it is impossible to drive between the rows. It is an acknowledged fact that the only way to secure a good stand, and give the trees a start, is to cultivate and take care of the plantings from the time of setting out. However, a number of groves have been set out on land that is too hilly or rocky to cultivate and the trees have made fair growths.
Thinning of the young trees is an important practice, as it is not good management to set out just the number of trees that one expects to mature. A planting upon any good soil may with advantage be set out 6 by 6 feet apart (1,210 trees to the acre), and at the end of the first year a rigid thinning should be started, removing with a grub-hoe all weak, inferior, or injured trees. This thinning should be conducted until only the strong and healthy trees, or a certain number, remain to the acre. By this method some trees will stand at the original distance that they were planted, while others will stand at multiples of that distance. The extra cost of close planting will never be noticed when the largest possible stand of healthy trees is guaranteed, which is practically the case under this method. If thinning is carried out by a set plan, removing every other one or two trees, many strong and healthy trees will be sacrificed. All limbs that have a tendency to deform the trees should be removed each year. After the third or fourth year, the trees will have grown to such a height that to remove the limbs may prove impractical in most cases.
At this period (the fourth or fifth year) there enters a new problem: the removal of the poorer trees for wood and stakes to allow the remainder a larger area of soil to draw upon and a greater space above ground to extend their branches. At this time the trees on an acre can be reduced to a certain number, leaving these to grow for telephone poles, ties, and lumber, or the entire grove may be cut for stakes and wood.
In three to six weeks after the trees have been felled, the sprouts will start out from the stumps. These sprouts are produced in abundance and if properly thinned will soon replace the cut forest, thus providing a second growth of fuel or timber in much less time than was required with the original grove. These remarks apply probably to all species of eucalyptus, certainly to all sorts experimented with in California up to the present time.
All of the keys used for the identification of species are more or less artificial. No satisfactory natural classification has yet been devised. While the following key is designed to aid in the making of determinations rather than to express relationships, species known to be closely related are placed near each other in the text so far as this can be conveniently done. For the ready determination of species in this critical genus, it is necessary to have adult leaves, buds, flowers, and mature fruit; immature fruits are often very misleading. Allowance should always be made for extreme forms, since only normal specimens are here described. This applies particularly to size of leaves. Unless otherwise stated, the leaf description is drawn from foliage on mature stems. The juvenile foliage, i.e., on young seedlings and on suckers, is usually very different, the leaves often broader, blunt, sessile, and of a different color.