Summary: When homeowners ask “How to Fertilize a Tree” it is often recommended that they broadcast fertilizer under the complete canopy of the tree, but is that the best way of fertilizing a tree? Let’s look at an alternative tree fertilizing method.
Question: I want to know the best way to fertilize a tree. I have heard of using a drop spreader to put fertilizer under the canopy, other people say to use fertilizer tree spikes. What say you on fertilizing trees in the yard? Kellen, Dothan, AL
Answer: Kellen, a tree expert looks at growing grass in shade in disgust arguing that the grass takes plant food from the soil for its own subsistence and robs the trees.
The sod grower looks skyward, shaking his head as he sees the stately oak living in luxury upon the food which is sorely needed by the struggling grass sometimes called a lawn under the tree.
Several factors enter in to the problem of establishing and growing grass under trees. It is necessary, first of all, to sow the right kind of grass seed.
Then, the grass and trees should be fed at regular intervals. Without enough plant food even the grasses proper for shade cannot survive. The theory of feeding trees is (and we are glad to have others share their views) that if you give a tree enough food the roots will not come up so near the surface to rob the grass of its necessary supply.
A good method of feeding trees is briefly described as follows:
The feeding roots of trees are located from the trunk out about as far as the branches spread, in fact, the root development below the ground usually balances the branch development above the ground.
To make plant food easily available to these roots it is necessary to distribute it pretty well underneath the spread of the tree. That is how many would recommend fertilizing a tree – spreading fertilizer on top.
A better way of applying fertilizer around a tree, especially if you plan on growing grass under the tree is to dig small holes about 10 to 12 inches deep at various places above the root system.
The necessary number of these is four times the number of pounds of fertilizer to be used according to the following table (this is an estimate):
- 10 foot trees – 2-1/2 pounds
- 25 foot trees – 16 pounds
- 50 foot trees – 65 pounds
- 100 foot trees – 250 pounds
Distance from tips of branches on one side of tree to tips on opposite side.
In other words a tree with a 25 foot branch spread would need 64 holes. About one-quarter pound of a good plant food containing a high nitrogen content would be poured into each hole with an improvised funnel to avoid spilling on on the grass.
This work will not harm the lawn if the sod is carefully cut out with a hand trowel before digging the hole. A crowbar or other sharp pointed tool is best for digging the holes.
After the fertilizer has been put in enough soil should be added to fill up the hole and then the sod can be replaced without damage to the lawn.
Most trees need to be fed occasionally but those suffering from disease or injury should be fertilized several times during the year. A healthy tree is able to resist the attacks of many insect enemies and diseases.