How to Fertilize Trees

Trees and Shrubs
Tree Fertilizer

Those who wish to grow trees in their gardens know that one of the most important things is fertilization. In order to make your tree grow strong and healthy, you need to fertilize it. However, not everybody knows how to fertilize a garden tree properly.

Common Problems with Tree Fertilization

The problem becomes even more complex when it comes to adequate application of fertilizer to benefit all the plants in the garden. For example, those who have a lawn as well as trees wonder how to spread the fertilizer to benefit both the grass and the trees. Sometimes, it seems that the common methods benefit either the grass or the trees at not both ones at the same time.

For example, one established wisdom argues for fertilizing under the entire canopy of the tree. Some people use a drop spreader to put the fertilizer under the canopy, but this is not the only method. Others prefer to use fertilizer tree spikes.

One thing to keep in mind when choosing the fertilization method is that your tree is not the only plant in the yard that needs your attention. The lawn itself needs to be fertilized properly. It is important to apply any fertilizer in such a way that will not harm grass on your lawn.

For example, what to do with the grass that is under the shade of the tree? If you fertilize under the tree, the grass can take all the plant food from the soil and thus will leave the tree without the important substances it needs for growth.

On the other hand, the opposite can also be true: the tree itself might thrive and leave the grass without any nutrients. Such grass will struggle so you won't be able to have a beautiful lawn under a tree.

Important Factors to Consider

Before you choose the method for fertilizing your tree, there are some important factors to consider. It is always best to prevent further problems by simply choosing the right kind of grass to plant. If you choose wisely, the grass will be able to thrive along with the tree. This is why picking the right grass seed is important. Always seek the one that is compatible with the tree species and variety that you have in your garden. Most importantly, make sure to plant grass varieties that can survive under the shade. Not all grasses love shade so make sure to choose the ones that can survive under the tree's canopy.

Another thing to keep in mind is timing. Your trees and grass need to be fed at regular intervals. It is important to provide your plants with enough food and nutrients that will make them thrive. Keep in mind that even the shade-loving grasses cannot survive under the tree canopy if there is not enough fertilizer.

The main idea behind proper fertilization of trees that will not harm the grass is simple: you need to give your tree enough food so its roots will not come up near surface to take nutrients away from the grass. If you follow this methods, you should be able to make both your trees and grass thrive.

There is a common problem with tree fertilization if you also want to grow a lawn. Not all grasses grow properly in the shade of a tree's canopy and there is a common problem on how to fertilize both. It is not unusual that the tree robs the grass and leaves it without nutrients. The opposite problem, in which the grass steals nutrients from the tree, is also relatively common.

In order to avoid these problems it is important to know how to fertilize a tree properly.

Basic Idea behind Effective Fertilization

Here is a basic idea behind effective tree fertilization. Since the goal is to have both the tree and grass use fertilizer nutrients effectively, they should not steal from each other. When does stealing happen?

Most commonly, this problem occurs when the tree's roots move way up, near the surface of the soil. This is when they compete for nutrients with grasses. However, tree roots should normally be located much deeper into the soil. The roots move upward when there is not enough nutrients in the depth of the soil.

In order to prevent the roots moving you need to provide your tree with enough fertilizer deep into the soil. This will allow the tree to use its nutrients but it will not use any fertilizer you apply to your grasses near the surface of the soil.

How to Fertilize a Tree Properly

Keep in mind that the roots of the trees go under the soil starting from the trunk to about as far as the branches spread. The root development under the soil typically follows the development of the canopy. This gives you the area you need to fertilize.

In order to get all the fertilizer to the tree roots, you need to distribute it evenly. Make sure to distribute it properly underneath the entire spread of the tree canopy. As noted in part I, many people simply spread the fertilizer on top of the soil, but this is where it may harm the grass or make the grass steal all the nutrients a tree needs to thrive.

This is why a better method is to dig small holes that are about 10 to 12 inches deep. Dig the holes all around the area that needs to be fertilized. Make sure to dig an appropriate number of holes that will correspond to the amount of fertilizer you need to apply.

This is how many holes you need: the number of holes is 4 times the number of pounds of fertilizer you need to use. The exact amount of fertilizer your tree needs depends on its size and species. Always ask an expert on how much fertilizer your tree needs to receive.

How Much Fertilizer: The Estimation

The estimates based on the size of the canopy seem to work well for many different tree species. In order to calculate this, you need to measure the distance from tips of branches on one side of the tree to the tops of branches on the opposite side of the tree.

Here are the quick estimates based on the size of the canopy (measured as explained in the previous paragraph):

10 foot: 2 1/2 pounds of fertilizer

25 foot: 16 pounds of fertilizer

50 foot: 65 pounds of fertilizer

100 foot: 250 pounds of fertilizer

Now, multiply the pounds by four to get the number of holes you need to dig around your tree. For example, if you have a 10 foot tree, you will need 10 holes. If you have a 25 foot tree, you will need 64 holes and 50 foot tree requires 260 holes. Large trees that are around 100 foot in canopy require 1000 holes.

When digging the holes, make sure to spread them evenly all around the area under the canopy. This is the only way to cover the entire tree root system and to get the nutrients to all parts of the roots. It is best to use a crowbar or another sharp, pointed tool to dig up the holes.

Applying the Fertilizer

Once the holes are ready, apply the fertilizer. It is best to use one that has a high nitrogen content. Simply pour the fertilizer into each hole. It is important to use an improvised funnel so you don't spill any fertilizer onto the grass.

If you apply the tree fertilizer in this way it will not harm the grass. Once the fertilizer is in, make sure to put in enough soil to fill up the hole.

Additional Information

Here is some additional info you need to remember about fertilizing your garden trees.

  • Healthy trees need to be fed occasionally. You should never forget to apply some fertilizer a few times per year.
  • Trees that are weak or suffering from a disease or an injury need to be fed more often, at least several times per year. Keep in mind that trees with a disease are not strong enough to resist insect attacks or new diseases so you need to keep them extra strong with a more frequent fertilization schedule.

Photo credit: Steven Taschuk

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