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Q: "After losing an old pine tree in my front yard, I'm determined to save its twin, which provides wonderful shade. One arborist says it needs "deep feeding," at a cost of $1,000. Another says a tree this old doesn't need such a treatment. What should I do?"

—Syndia Marxer, Chandler, Ariz.

A: I believe that a tree in distress, no matter how old, can benefit from deep feeding: having fertilizer injected through a needle about 6 to 18 inches into the ground, beyond the reach of greedy grass roots. But if your tree is healthy and pushing out plenty of needles every spring—it certainly looks to be in good shape in the photo—then deep feeding probably isn't necessary.

That said, your tree may benefit from some extra attention to its root system because trees in streetside locations are vulnerable to all sorts of stresses, such as heat, drought, car exhaust, and the like.

First, test the soil to find out exactly which minerals, if any, are lacking. Then, if fertilizer is needed, spread it in early spring or early fall after removing any grass or mulch around the tree. At the same time, top-dress the area with 1 to 2 inches of compost, and work it into the soil with a rake. Compost encourages the growth of beneficial mycorrhizae, soil fungi that enhance the ability of roots to absorb nutrients. Finally, cover the soil with mulch, keeping it 3 inches from the trunk.