| Sub-surface feeding, above, and below, surface feeding by injection. |
Photos courtesy of Tree Injection Products Co.
"Turf and trees aren?t the best of friends," says Chris Nasca, supervisor and consultant for Arborguard Tree Specialists in Avondale Estates, Georgia. "Turf robs trees of nutrients in the soil because turf consumes nitrogen a lot more than trees do. Some think they fertilize the lawn and at the same time take care of the trees. But this isn?t so."
The nutrient requirement for trees is high. In most cases they are competing with turf and other woody plants in the landscape. While some will argue that a surface application of fertilizer is sufficient for feeding trees, Nasca feels it?s best to use a high nitrogen mix injected below the turf roots, which live four to six inches underground.
Thomas Schmitt, an ISA certified arborist with Knoxville, Tennessee-based Cortese Tree Specialists, agrees with Nasca. "When feeding trees with broadcast spreading over the ground, tree roots are only getting two to five percent of the nutrients if there?s a full lawn in place," explains Schmitt. "The best method for feeding trees is soil injection, with a slow release fertilizer. A good rule of thumb is to use up to four pounds of nitrogen per 1,000 square feet. Use as slow a release as possible." In turf areas, this slow release is important, as a one-time application would result in fertilizer burn on the turf.
Fertilizing a tree increases controlled growth, reduces susceptibility to disease and pests, and can even reverse deteriorating health.
But to know when a tree needs the extra push of a fertilizer, or supplemental nourishment, takes a keen eye and tree knowledge. Some ways to tell if a tree needs to be fertilized include:
Small leaf size.
Unusual or darker-than-normal leaf color.
Reduced twig growth.
Evidence of crown dieback (the gradual death of the tree?s upper part).
Of the points mentioned above, twig growth is used most frequently to determine a tree?s general health, and can be shown to a property owner to justify the need for care. The distance between bud scale scars (the ring around a twig) provides an excellent indication of a tree?s growth rate. The scar ring near the branch tip shows where growth started last spring. The bud scar near the base denotes where the previous season?s growth started. By locating scars for the past three to four years, the rate of growth can be accurately determined. According to the Texas Agricultural Extension Service, young trees should have at least nine to 12 inches of terminal growth per year. Large, mature trees usually average six to nine inches of growth.
But, just as beneficial as fertilizing can be, it can also be detrimental to the tree. Soil conditions, especially pH and organic matter content, vary greatly, making the proper selection and use of fertilizer somewhat tricky. Not to mention the numerous species of trees, which Jim Skiera, associate executive director of the International Society of Arboriculture, sees as a job of precision--matching the right fertilizer with the right tree.
"There?s no silver bullet in knowing tree care across the board," says Skiera. "With turf you have one or two turf species within a lawn, but on a residential property you may have 15 to 20 different species of trees. And in most situations, the turf roots and tree roots are intermingled."
This intermingling of roots is touchy, as broadleaf herbicides have the potential to be picked up by the trees? roots, setting up a chance of killing the tree. One possible solution to this dilemma is mulching. "Mulch as much as possible," advises Nasca. "You like to see mulching away from the base of the tree, going out as far as you can go."
Two tests can be done to determine a specific tree?s fertilizer requirements: a soil test, and a foliar (leaf sample) analysis. Instructions for taking samples for either test can be obtained from your county Extension office. This is a good idea, as it will minimize waste and the possibility of pollution. It also provides a scientific justification to show a customer that their trees need your care.
Although anyone can attempt a complete tree care program as a do-it-yourself project, Skiera recommends employing the expertise of an arborist, either as a subcontracted agent or on staff. "It?s a good marriage, having an arborist on staff," says Skiera. "It?s an unrealistic expectation that one person can know everything. But you can train your field people to recognize the basic things, and then have a tree specialist come out. You can also have an arborist do an on-site inspection before taking on a new project."
(leaf sample) analysis.
This specialized area of tree care is even more relevant when caring for trees in urban locations, such as in malls and parking lots. In those places you?re getting into extremes," says Schmitt. "The heat coming off the hard surfaces can be 10? to 15? above the surrounding air. These trees are twice as stressed as normal trees, and are more vulnerable to disease and pest problems."
"In the more intensive urban areas, the roots of the tree are typically restricted," notes Skiera. "Those trees tend to require a more intensive program of care. Keep in mind that if you take on a tree care program, ongoing assessment will be necessary."
"There is also a safety issue," says Skiera. "You should have a risk assessment program that?s going to identify if there are hangers, or dead limbs, because the potential for someone to get injured is there." This ongoing inspection works well for the landscape contractor since he?s on site on a regular basis anyway.
Thinking of taking on the tree task at hand? You?re in luck! An opportune time to introduce this new service is on the National Millennium Arbor Day Celebration, April 29, sponsored by the International Society of Arboriculture.