Home Is Where Your Trees Are

Tree Structure. Roots. Part 3

Moreover, Mr. Stout claims, sod does not restrict the air and moisture of tree roots. On the contrary, sod breathes better than baked bare ground and it slows the evaporation of moisture from beneath it. As for competition for nourishment between surface growths and tree roots, Mr. Stout believes the latter can more than hold their own. This has been shown by experiments in dense woodland where the absence of grass and weeds from the forest floor might have been supposed to be caused by shading. Ten-foot squares between groups of trees were trenched around to a depth well below the tree roots, which were all cut off as encountered. The trees' heads were left untouched, their shade unbroken. Within a year, each square filled up with surface vegetation, flourishing in the forest gloom wherever it had no tree roots to contend with. Experts to the contrary notwithstanding, Professor Stout believes that broadcasting dry fertilizer to trees is surer, sounder, more economical practice than punching it down.

He concedes that where tree food is broadcasted, spike-rolling the sod might be wise to speed the fertilizer's movement downward, and that when the needle or punch-bar methods are used, their efficacy can be improved by doubling the points in the usual pattern - i.e., putting them only one foot apart instead of two - and halving their depth, to nine to twelve inches. Mr. Stout believes that most tree feeding is more arbitrary and haphazard than it might be. He recommends that before any feeding is done in their grounds, home owners dig some test holes to find out just how their soils lie and their tree roots run, then serve them accordingly.

No matter how food is administered to it, on the ground's surface or down under, a tree's alimentary process remains the same. Like native minerals in the soil, the water-borne nutrients of fertilizer do not go directly into the tree's tissues. They must first be imbibed by rootlets, then carried aloft by the pumping system to the leaves, to be transformed and elaborated by photosynthesis. The three prime nutrient minerals are nitrogen, phosphorus, and potassium. Nitrogen plays the leading role in forming chloroplasts, the green bodies that change sun energy into chemical energy. Phosphorus is ingested by the leaves in such a way as to stimulate flower, seed, and root growth. Potassium (potash) adds tensile strength to wood cells and, in the leaves, it catalyzes the formation and movement of sugars and starches, formed by carbon, hydrogen, and oxygen from the tree's air and water. In selecting a manufactured fertilizer for trees, the ordinary commercial brands made for farm use will serve, but some of the mixtures prepared expressly for shade trees are better, and probably worth the difference in price. The nitrogen-phosphorus-potassium ratios are usually printed on the bags in bold figures.

Most formulas meant for crop tillage (5-10-5, 6-8-6, 10-10-10, and the like) are lower in nitrogen than are most tree formulas, which will run 10-8-6,10-6-4,or maybe 8-6-8. Most field f ertilizers come as finely divided powders intended to dissolve rapidly. Tree foods are milled in coarse granules for a slower, longer lasting effect. The better prepared tree foods incorporate at least some of the trace minerals, such as boron, magnesium, and manganese, which trees are now believed to require. Coming out of dormancy in the spring, a tree puts most of its energy into growth through all its upper parts. As summer wanes, energy is transferred to extending and strengthening the roots and to storing up a reserve to start new growth in the spring. Hence autumn feeding and spring feeding have different effects. On the whole, and especially for trees whose size is satisfactory, autumn feeding is best, from the September rains until hard frost. For trees whose size it is desired to force, or whose vigor was low last growing season, spring feeding is preferable, from mid-March to mid-June in temperate America. In the deep South and arid West, variations will be dictated by expectancies of heat and rainfall. Old trees are sometimes likened to freight trains for the momentum of their growth or decline.

When a thriving old tree suffers hardship in its roots, such as disturbance by bulldozing, or successive years of drought, or a severe and snowless winter, the effects may not show up for some time, and then only gradually. The tree's stored up energy, like a freight's ponderous headway, keeps it "coasting." Signs of decline to watch for, apart from obvious die-back and deadwood aloft, are decreases in the length of annual twig growth, and in the size and greenness of the leaves. But after the occurrence of a hardship, it is better not to wait for trouble signs. Feed the tree and fend them off. Bulldozing has been mentioned as a threat to tree roots. Not only the blade and crushing treads are to be feared. The machine's mere weight can so impact the soil that it becomes impervious to air and moisture. And in grading, any overlay of soil more than three or four inches deep is likely to suffocate the sturdiest root systems.