PECAN Trees Require Abundant Sunshine and Space
Abundant sunshine and free space are no less essential to the parts of a pecan tree that are to produce their share of its crops than is liberal plant food in available form and space to the roots. This fact did not receive the attention it demanded from most of the pioneers in the industry who were the first either to top-work the wild groves of the Southwest or to plant the first orchards farther east.
The pecan tree is the largest growing nut tree under orchard cultivation. The average spread of ordinarily big trees, 50 or more years of age, standing in the open and in locations favorable to their growth is probably from 100 to 125 feet, although maximum trees of materially greater range are not unusual. This is fully three or four times the usual size of normally big apple trees and from four to six times that of the peach, yet many of the first pecan developments were spaced at from 15 to 30 feet, which represented the usual planting distance of these species at that time.
The planting distance between pecan trees has increased an average of approximately 1 foot a year since 1900. It was then about 35 feet. At present, few orchard trees are being set less than 60 feet each way. The end is apparently not yet in sight as 100 feet is being speculated upon and occasional orchards are being so spaced.
Evidence of greatly reduced bearing surface in the lower parts of the trees because of the shading and subsequent death of, first the fruit spurs and then the entire branches, is to be seen in nearly every orchard of the South that has made normally rapid growth and has been of adult bearing age for more than five years. The branches of many of these earlier plantings form a canopy from 20 to 50 feet high from one row to another, below which there are few or no bearing branches except on the outside of the end rows.
There is but one remedy to apply, once crowding has begun; namely, to eliminate some of the trees. This costs money and takes courage, especially as not infrequently crowding has begun before the trees have begun to bear profitably.
Regardless of whether or not the trees are destined to become profitable in later years with thinning, they are most unlikely to do so without it, once serious crowding has begun. As to the exact time at which they should be thinned, much will depend upon the variety, original spacing distance, rate at which they have grown, and various other factors. Some varieties are less promptly affected by shade than others, either because of greater ability to endure shade or because of an erect habit of growth and the causing of less shade, or both. The Stuart affords a good illustration of the upright-growing type, very resistant to shade, and requiring a minimum of actual space during a long part of its early bearing period, and the Frotscher, an equally good illustration of a variety that is both broadly spreading and intolerant of shade.
The extent to which the branches of the trees in an orchard may come together at the middles and serious shading begin is shown in Figure 168 photographed near the end of the fourteenth growing soason after the trees had originally been set out 50 feet each way. The damaging results of shading were much in evidence at harvest time of the year in which this picture was taken. The leaves on the lower branches matured and dropped prematurely and the nuts from the same branches were so poorly filled that they seriously lowered the average condition of the entire crop.
One year later the branches crossed the middles of the tree rows to such extent that the vision was entirely obstructed and great spaces became vacant about the lower parts of the trees where recently there had been heavy-bearing branches. It was then so obvious that the process of self-pruning was likely to continue indefinitely unless prompt action was taken that the alternate trees in the part of the orchard where they were the largest and incidentally the best bearers, were removed.
None of the trees in the outside rows were disturbed, as these had one side on which they were free to develop. The lower branches on the inner sides of these trees continued to drop off as shown in Figure 169, by which it may also be seen that those on the outer side were still being retained seven years later when the picture was taken.
Following the removal of the alternate trees, not only did the lower limbs cease to die but those not too far gone put out new leaves and spurs and began again to bear crops. The filling quality of the nuts was restored to normal and the yields per acre continued to show a satisfactory increase. The ends of the lower limbs began to sag with weight of nuts and to again occupy the space which had been vacant.
A typical view between the trees, taken seven years after the thinning process took place, on the diagonal, which had become the order of alignment with the thinning process, is shown in Figure 170. This shows that it will probably be only a few years before the branches will so overlap that thinning will again be advisable.
