Fertilizer is NOT plant food. Trees, like all green plants, make their own food. Fertilizers contain elements essential for tree growth that may be missing from depleted soils.
For the first year after planting, trees and shrubs need no additional fertilizers, and those treated can probably fend for themselves. Likewise, mature established trees need no extra nutrients when grown in healthy undisturbed soil. Most gardens, however, contain trees and shrubs planted for the gardener’s pleasure and not because that’s where they would naturally grow. That’s why they need the occasional nutrient boost that a fertilizer gives.
Fertilizers vary in their mix of the basic nutrients: nitrogen, phosphorous, and potassium. Nitrogen promotes leaf an stem growth, phosphorous and potassium support flowering and root development.
Whenever you read a fertilizer label, the numbers representing the percentages of each nutrient always appear on the label in that order. This is true whether the fertilizer is granular, liquid or soluble powder.
Organic Approach to Fertilizing
Instead of using fertilizers, organic gardeners keep their soils healthy with compost, a jumble of decaying organic matter such as leaves, clipped grass, and worm casings, that enhances soil structure and supplies nutrients to plants.
An excellent nitrogen-rich organic soil additive is rotted manure of bats, cows, chickens, and horses. Sometimes you can find dehydrated, pelletized, composted manure packaged as an easy-to-use organic fertilizer.
Other organic fertilizers range from liquids made from fish and seaweed to bonemeal, blood meal, cottonseed meal, and alfalfa meal. Organic fertilizers not only supply necessary nutrients, they usually condition the soil, adding organic matter and improving the soil’s moisture an nutrient retention. Follow the package directions to establish the necessary amount for your plants and trees.
If you prefer using synthetic fertilizer blends, then it’s even more important to understand how much of each nutrient you need. You can discover that information form a soil test.
Dry granular synthetic fertilizers are cheap and easy to apply but they must be watered in to release their nutrients. The idea ratio of NPK for trees is about 3:1:1. Thus, if you see a product labeled 27-9-9 or 30-10-7, it would fall into this range.
If you broadcast fertilizer, keep it off your driveway, patio, and walkways, because rain or sprinklers can wash it from your property and into drains and culverts, eventually spilling into nearby bodies of water.
Also make sure you apply fertilizer at the correct rate and in the right location, because a tree’s root zone may expand in any direction two to three times the radius of the crown. For instance, if the crown of the tree is 15′ wide, keep the area closest to the trunk and apply the granules under the canopy starting 5 feet from the edge of the crown to about 15 feet beyond it.
You may want a tree service to inject a liquid product into the root zones. Most tree roots that take up nutrients exist in the top 6-8 inches of soil, so deeper injections are unnecessary and not as useful to the plant. if a tree grown in lawn, an arborist will feed it just below the turf roots.
*This information was provided by the Homeowner’s Complete Tree and Shrub Handbook.