But fertilizers, especially those containing nitrogen, can actually mask many other landscape problems. And they can accentuate pest problems. Unfortunately, heavy fertilization and the resulting deep green landscape pose many problems for trees, especially large, old trees. Many of our trees are overmedicated. Large doses of fertilizer, applied in one massive lot, are far from the slowly metered, small portions released in the forest's recycling organic layer.
Every excess has a price.
For trees, excess nitrogen requires the tree to use immense amounts of root food reserves. That takes these reserves away from other uses. The mulch should be renewed often, but never allowed to build up. Another practice for good tree life is to apply just a little nitrogen fertilizer just after full leaf expansion in late spring. Base the nitrogen amount on the square feet of open soil surface beneath a tree.