We’ve said it before and we’ll say it again (and again, and again!): soil is one of the most crucial factors in the healthy growth of your trees. From the moment it’s planted, your tree will rely on its bed of soil to deliver necessary nutrients, water, and oxygen.
Of course, not all soils are created equal—and neither are trees. One species of tree may require a different balance of nutrients and a different pH level from another, and when the soil it’s planted in isn’t providing that balance, you’ll start to see symptoms of nutrient deficiency in your tree’s growth. These signs could include yellowed leaves and slowed growth of new shoots.
If you suspect that your tree could be suffering from a lack of proper nutrition, then fertilizer could be the answer. Fertilizers supplement the soil’s macronutrients (nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur—elements your tree needs in large amounts) and micronutrients (iron, copper, zinc, and others—of which your tree can survive with smaller doses). They can also be used to correct improper pH levels. Most fertilizers are labeled with the percentage of nitrogen (N), phosphorous (P), and potassium (K) they contain, displayed as N-P- K (9-18- 9, 24-0- 15, etc.).
Because of each tree’s unique nutrient requirements and soil’s unique nutrient content, it’s important not to grab just any fertilizer off the shelf in the gardening section, or to assume that the fertilizer you laid down for your lawn will be sufficient for your tree, too. And if nutrient deficiency or pH imbalance turn out not to be at the root of the problem, then no amount of fertilizer will be the solution. Before you reach for any old bag of 12-12- 12, we strongly recommend having a soil test performed to find out just what’s missing from your soil. Compare the results of the soil test with your research about what your tree species needs from its soil, and you’ll have a much better idea which fertilizer to choose.