A Prairie Garden Journal    by Dick Meyer

 It's Time

To

Fertilize

Trees
 

Just in case you’re planning to use the long 4^th of July weekend to catch up on some of those spring and early summer landscape tasks delayed by this spring’s stormy weather, consider this week’s column a friendly reminder of the importance of fertilizing trees.

How can I tell if I should fertilize my trees?
Young shade trees (less than 20 years old) should grow at the rate of  1 ½ to 3 feet per year, and in mid-summer, their leaves should have a dark green color.  If your trees are not growing this fast or don’t have dark green leaves, they need to be fertilized.   Young evergreen trees should grow at the rate of 1 to 2 feet per year. 

What kind of fertilizer do trees need?
In western Nebraska and eastern Wyoming, trees actually need two different kinds of fertilizer.  For ease of understanding, let’s call these two different kinds of fertilizers major element fertilizers and minor element fertilizers.   Major elements fertilizers are often the only fertilizers used for trees, but in western Nebraska and eastern Wyoming, it may actually be more important to apply a minor element fertilizer to your trees.  This is because a tree that is deficient in any of the minor elements cannot effectively use the major soil elements that are contained in the major element fertilizers.  So if you only have time to apply one type of fertilizer to your trees, I recommend doing the minor element fertilizing first. 
 

Previous Articles

Yes It's Time March 12

Pruning Trees March 26

Plant a Tree in 2009 April 02

Great Old Trees April 09

"Nightmare on Elm Street?"
Elms & Oaks for WyoNeb
April 16

Green, Easy & Cheap April 23

No GardenSpace? No Problem
April 30

A Mother's Garden May 07

What Makes a Good Perennial?
May 14

Summer School - Kids Gardening
May 21

Do it yourself Landscape Planning
May 28

Butterfly Gardening June 4

Versatile Viburnums June 11

Perennial Shrubs June 18

Theatre West Garden Walk
June 25

What is a major element fertilizer?
Major element fertilizers are the traditional fertilizers similar to those that you use on your lawn.  They usually contain the elements nitrogen, phosphorus, and potassium.   The label on the fertilizer product should tell how much of each element is in the fertilizer product.  This information is usually contained in a three number formula on the label.  The first number is the amount of nitrogen, the second number is the amount of phosphorus, and the third number is the amount of potassium.  For trees, I recommend a fertilizer that contains from 10% to 20% each of nitrogen and phosphorus.

 When should I apply a major element fertilizer to my trees?
Apply a major element fertilizer to your trees any time during the months of June and July.   Fertilizing trees with a major element fertilizer in early spring (before May 15), or in late summer (after August 1), may actually do more harm than good, so timing is important with a major element fertilizer.

How much major element fertilizer should I use for each tree, and how do I apply it?
A good rule of thumb is to fertilize all of the area under the branches of a tree plus another 5 feet or so.  Use the following table to determine how much major element fertilizer to apply to each tree.         

The easiest way to apply the fertilizer is to spread it like you do a lawn fertilizer, using either a drop spreader or a “whirly-bird” fertilizer spreader.   If you have a nice, large circle of mulch around your tree (8’ diameter circle or larger) you may elect to simply spread about 2/3 of the amount of fertilizer suggested above within that mulch area, and water it in thoroughly.

What about minor element fertilizers?
When discussing fertilizers, the term “minor elements” generally refers to the following chemical elements which plants generally need in relatively small quantities:  sulfur, calcium, iron, zinc,

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 magnesium, manganese, copper, boron, molybdenum, and chlorine.  But just because they are needed only in small quantities does not mean that plants can get along without them.  The yellow leaves and stunted growth of trees and shrubs that are deficient in minor elements is a dramatic illustration of the importance of these so-called “minor elements”, and minor element deficiency is a very common problem of trees and shrubs growing in Wyobraska landscapes. 

There are two easy ways to help your trees get the minor elements that they need for healthy growth. 

One way is to take out an 8’ diameter circle of grass around the tree, then spread 5 pounds of sulfur and two inches of a good compost over the entire circle and very lightly work the sulfur and compost into the top two or so inches of soil.  Finally place 3 inches of a wood chip mulch over the top of the compost.   The sulfur will help make the minor elements in the existing soil more available to your tree.  Compost is rich in minor elements, so the two inches of compost will be like a fertilizer, and the mulch will help promote extensive root growth, which will help your tree take in more minor elements.

 Another way is to use a fertilizer product that contains minor elements.  Most of these products must be applied by digging or augering small holes under the canopy of the tree and placing a certain amount of fertilizer in each hole.  Each product will have specific directions, so take care to read the directions before applying these products.

In my experience, these are the two most effective ways to “fertilize” your tree with minor elements.  You can perform minor element fertilization any time of year because minor elements do not stimulate new growth, they only allow for healthier growth. 

"It is most important to apply a minor element fertilizer to your trees.  This is because a tree that is deficient in any of the minor elements cannot effectively use the major soil elements that are contained in the major element fertilizers."