Home Is Where Your Trees Are

Tree Structure. Roots. Part 2

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: 1. Roots reach out much farther than you think, as much as twice the reach of the crowns. 2. 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.