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Nitrogen Fertilization

Filed Under:
Publication Number: IS1978
View as PDF: IS1978.pdf

of Landscape Trees and Shrubs

Figure 1
Figure 1. Example of the proper area to fertilize a landscape tree and how to measure the distance from the trunk to the edge of the canopy.

Fertilizing trees and shrubs in the home landscape supplies nutrients and encourages growth and flowering. Fertilization may help newly planted shrubs or trees become established. Nitrogen fertilization is usually done to promote growth and enhance the appearance of ornamental plants.

You may also need to fertilize to correct other nutrient deficiencies. To determine which nutrients are deficient and how much fertilizer you need to apply, you should take a soil sample and follow the soil report recommendations. Information on soil testing is available at your county Extension office or online at extension.msstate.edu.

This publication will help you determine appropriate amounts of several commonly used nitrogen fertilizers you would apply to plants in the landscape.

Fertilizer Timing

The best time to fertilize trees and shrubs with nitrogen is during the growing season. In most areas of Mississippi, this is from April to October. Take care to avoid using high-nitrogen fertilizers too late in the year. This can cause a flush of tender growth that may be damaged by freezing temperatures.

Newly planted trees and shrubs benefit from nitrogen fertilization in the spring and again in the late summer. Wait at least 4 weeks after planting before applying any fertilizers. This will allow the root system to become established and absorb nutrients to stimulate new growth and development. Well-established trees may benefit from an annual application in the spring. On extremely sandy soils, split fertilizer applications are needed. This means you apply the same amount of fertilizer, but divide it into multiple applications spaced out over a period of time.

Fertilizer Application

Fertilizer should only be applied to the targeted plants in the landscape. Spread it uniformly across the root zone of the plant. In most cases, this means underneath the canopy of the plant (Figure 1).

Table 1Areas where landscape plant fertilization zones overlap with lawn fertilization zones should be fertilized for one or the other, but not both.

Read the label on the fertilizer bag and be aware that some lawn fertilizers can contain herbicides that are detrimental to landscape plants.

Nitrogen Fertilizer Rates

Most established landscape shrubs should be fertilized with N according to the rates in Table 1. Always follow a soil test recommendation for other nutrients. The required amount of several commonly used nitrogen fertilizers is found in Table 2. Following are some

formulas that help determine the amount of fertilizer needed for products that are not listed in this publication or for larger areas.

Slow- or controlled-release fertilizers are preferred, but similar results can be obtained by applying small amounts of soluble fertilizers more frequently. If you apply water-soluble fertilizers, the applications should be split and applied at a rate of no more than 0.5 pound N per 1000 square feet at a time. Do not apply fertilizer when heavy rains are imminent.

Formulas

Use the following formula to determine how much fertilizer is 1 pound of N per application. All you need to know is the first number (N) from the fertilizer bag.

Lb fertilizer needed per 1000 sq ft = 100 ÷ (N on fertilizer bag)

Use the following formula to determine how much fertilizer is needed to fertilize a given area. You need the answer from the equation above and the size of the area to be fertilized.

Total lb fertilizer needed = (answer from above) × (sq ft of area) ÷ 1000

To determine the size of the area under the canopy, use the equation below. Measure the distance from the trunk to the edge of the canopy. See Figure 1. This answer can be used in the equation above.

Area under tree canopy = 3.14 × distance from trunk to canopy edge × distance from trunk to canopy edge

Table 2Caution: This information is for educational and preliminary planning purposes only. Use this table only as a guide. The user assumes the risk of using or otherwise relying on the output of the table. Mississippi State University Extension Service does not warranty the functionality of the table and concedes that errors can or will be discovered or corrected. MSU Extension does not warranty the accuracy or completeness of any output from the table. The table, its use, and its output is provided “as is” and without any expressed or implied warranty, including merchantability or fitness for a particular purpose. The Mississippi State University Extension Service is not bound by any table output and is not responsible for use or reliance on any such output.


Information Sheet 1978

By Karl K. Crouse, PhD, Associate Extension Professor, and Geoffrey C. Denny, PhD, Assistant Extension Professor, Plant and Soil Sciences.


 

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