To Keep A Tree Fit And Stable, Its Roots Must Be Visualized And Tended

The upper parts of a tree inevitably monopolize our attention. The trunk and crown, the leaves, flowers and fruit, are what we can see and enjoy. When they think about their trees' care, owners are prone to ignore the root systems—out of sight, out of mind. And this imbalance of emphasis is not confined to laymen. The scientific study of roots has lagged far behind other branches of dendrology.

A few years ago an important but not widely publicized contribution on root systems was made by Benjamin B. Stout, now on the Rutgers forestry faculty. He and two assistants spent the summers of 1951-52 in Harvard's Black Rock Forest near Cornwall-on-Hudson, N.Y., laboriously exploring trees down under. Mr. Stout selected twenty-five typical specimens representing nine deciduous species, all growing in light, comparatively shallow highland soils, and ranging in age from 17 to 104 years, in height from 21 to 67 feet.

The digging was to be done hydraulically, with strong jets of water to unearth and gentler streams to wash clean every part from deep taproots to the hairy tips of long laterals. So trees on sloping sites were chosen, to let the hose-water and soil drain away. This also made it easier to photograph the naked root systems in profile. (See Photo. 2.) Before its roots were laid bare, each tree was felled and its upper parts laid by for correlative study.

Mr. Stout's measurements, ring counts, and other data were illuminating not only to dendrologists. They also contained broad hints for home owners. Most importantly they revealed that the average tree's root-spread is far wider than had been supposed. Instead of approximating their crowns' spread, the roots of Mr. Stout's trees reached out into areas 3.4 to 40.7 times as great as the ground-space under the crowns. (See Photo. 2 and diagrams following p. 48; also diagrams pp. 15Q, 160. Dotted lines show crown areas, as contrasted with root reaches in solid line. Graphs give stem (—0—) and root (—x—) growth data in feet and years. Circles initialed CO, WO, RM, etc., denote neighboring chestnut oak, white oak, red maple, etc.) Eighteen of the trees appeared to have normal root systems; for these, the root-crown ratio averaged 4.5 to 1. Since the Black Rock trees had grown under forest conditions, with their crowns touching, this meant that each tree was competing for sustenance with at least three of its neighbors.

Where adjacent trees had been removed by natural death or foresters' thinning, in known years, the trees under study had responded, as shown in growth rings, by quickly extending their roots as well as their branches.

Roots were found to vary surprisingly in age. And some of the younger ones were among the longest.

"The many-aged nature of the roots," wrote Mr. Stout, ". . . suggests that throughout the life of a root system there is a continuous process in which the old roots die off and new roots emerge. If this is the case, then there would be, coming from the stump and major laterals, waves of new roots that would occupy and reoccupy the soil."

Mr. Stout ventured no scientific generalizations from his limited study, but two conclusions for home owners seem fairly dependable:

Roots reach out much farther than you think, as much as twice the reach of the crowns.

Mature trees keep growing new roots, and this process can be encouraged.

These aspects of subterranean structure and behavior are important to have in mind when trees are fed, as they must be to keep them fit. It has always surprised me to find how few tree owners, new ones especially, truly realize that trees feed just as other plants do. Under lawn conditions, where dead leaves and even grass cuttings are removed from the natural organic supply, substitute food must be made available if a tree is to live its full, vigorous life. To keep them in prime shape, normal yard trees should be fed every two or three years, weaklings annually until they flourish.

The feeding of trees has long been standardized by the tree-service profession, of whose annual income it provides a large part. Their techniques will be described, adapted to home practice. But Professor Stout takes exception to some "expert" practices, and his thinking will also be explained. Perhaps the best way lies somewhere between.

Most experts believe that broadcasting fertilizer to trees, except to the shallow-rooted evergreens, is a waste of time and money, a fine way to grow grass, weeds, shrubs, and unwanted tree seedlings. By thickening the turf, surface fertilizing also tends to lessen the tree roots' water and air supply, it is said. The usual professional method of tree-feeding is to thrust food down to where the roots run, or even lower to attract roots downward and improve their grip on the ground.

For home owners, one of the handiest tools for feeding trees is the injector probe or "needle." This is a hollow steel rod three or four feet long, sharp and perforated at the business end. It has a glass or plastic chamber at the top, under the handle, to contain a cartridge of food concentrate. It attaches to your garden hose. It costs up to eight dollars, the cartridges about twenty-five cents each. One cartridge will dissolve in and sufficiently enrich about 100 gallons of water, enough to invigorate a twenty-inch diameter tree. (The approximate diameter is one-third of the length of a string that will encircle the trunk, breast high.) With forty pounds of pressure on your water line, in moderately loose soil, one hundred injections of about a gallon each can be put down in less than an hour. Your hired man can easily "needle" a dozen average trees in a day, or you can do as much yourself over a lazy weekend without blisters or a sore back.

Liquid feeding by injection is a short-range method. Its effects are quick but transient. It is valuable for trees needing a prompt shot in the arm, since the nutrients are immediately available, in aqueous solution. But much virtue may leach away before the tree has imbibed all its needs.

After anemic trees are thus invigorated, the experts recommend a lasting supply of solid food, such as suffices for non-critical cases. The home tool for this is a punch-bar, pointed at one end, wedge-shaped at the other. Any schoolboy of moderate strength can learn to drive the wedge into turf at an angle, to raise and lay back a broad divot. From the opening thus made, a pound or so of soil is scooped out and piled nearby for replacement later. The bar's sharp end is now plunged into the hole repeatedly, deeper and deeper. Work the buried point back and forth on each stroke to loosen the subsoil and at the same time ream out the hole's mouth. Rocks and hardpan permitting, the holes are driven 18 to 24 inches deep.

Dip a pound or two of tree food from the bag or pail you carry it in and funnel it down the hole, making sure it reaches the bottom. Don't fill the hole with food to the very top. Leave room for your pile of loose soil, with the divot replanted over it. Tamp down the divot and you would never know your lawn had been punctured. You wouldn't, that is, if your top fillers of loose soil were thick enough. If they weren't, a handsome "cow's tail" of lush grass will rise over each feeding spot.

Perfectionists at tree feeding sometimes employ the round "cookie cutter" used to incise putting holes on golf greens. With this tool the turf divot and replacement soil-plug can be controlled precisely. But, as with an earth auger, this technique is tedious and it leaves you with an overage of displaced soil to carry away.

The approved pattern for feeding a tree by needle or punch-bar is a series of concentric circles around the trunk, beginning halfway out to the crown's perimeter and extending as far beyond it. Space the circles two feet apart and the insertions along them a like distance. Slant the tool inward toward the tree to increase the food's coverage. Figure five pounds of dry food for each inch of trunk diameter. For trees under eight inches, halve this ratio. Where obstacles like buildings or pavement limit your pattern, follow it as far as you can, but don't overload it.

Professor Stout's objections to the orthodox tree-feeding techniques thus summarized are based on the very simple fact that fertilizer placed on or in the ground can go nowhere but straight down. Aqueous food solutions fed under pressure by needle may diffuse sideways somewhat, but dry deposits put down by punch-bar will only sink vertically as they dissolve. Except where the needle or bar happens, by blind chance, to strike into roots or to stop just above them, the fertilizer misses its mark.

There is no evidence to suggest that tree roots have the faculty of searching out food deposits in the same way as they will grow toward a continuing source of moisture. Even if they had such a faculty, Mr. Stout argues, it would not be good for them to exercise it, because they would then concentrate root growth at the points of feeding, which are only temporary. This is exactly what takes place when you do happen to hit a root with a food deposit. The dense feeder ganglia that form, at the expense of root growth elsewhere, give the tree an abnormal root pattern, vulnerable to drought.

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.

A Canadian doctor named Locke used to ascribe most human ailments to deformations of the feet, brought on by wearing badly designed shoes. Some dendrologists similarly believe that more tree ailments than we suspect are caused by root deformations. Commonest of these, and easiest to discover and correct, are so-called "girdling" roots, where one crosses and constricts another close to the trunk, or constricts the trunk itself. The effect on the tree's circulation is precisely that of a tourniquet around your leg, or a noose at your neck. Any home owner with a pick and shovel can expose such conditions for himself. When they are not visible above ground, their presence can be suspected wherever one side of a trunk comes up straight out of the ground without the flare of buttress roots. For a typical case of detection and exposure, see Photos. 3, 4, 5.

Without benefit of a trained tree surgeon, the offending root can simply be dug around and cut away from its victim for several inches on both sides of the stricture. If it is a big root, six inches or so in diameter, the operation is best performed in two stages to lessen shock to the tree. The trick here is to use a chisel instead of saw or ax. First cut away the under half of the constrictor, to relieve its pressure yet let some of its own sap supply continue. (See Fig. 2.)

Complete the operation a couple of seasons later, meantime stimulating an adjusted root growth by well-placed feeding.

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