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Should You Apply Fertilizer to Trees?

Discover the importance of fertilizing trees, how to select and apply the right fertilizers, and the impact on tree health and growth.

Table of Contents

A tree requires nitrogen, zinc, iron, phosphorus, and potassium for growing roots, leaves, flowers, and fruits. The soil may lack the right amount of minerals to support this growth. Here, fertilizers can add adequate nutrients to the soil, promoting healthy roots and branches. 

The right amount of fertilizer can keep the old trees healthy and help the new trees establish a good root system for upcoming years. You may improve the fruit and flower production in a tree with the right fertilizer ratio. Since trees last for several years, it’s necessary to take care of their requirements in a timely manner. 

Along with tree fertilizer, you may adjust the watering needs and mulching to keep the trees thriving through different seasons. In this article, we’ll cover if and why trees need fertilizing, the best way to add fertilizers, and which ones to pick. 

The Need for a Tree Fertilizer

The Need for a Tree Fertilizer

Learning about the soil and tree needs can be insightful in deciding the best option. Here’s how you can do it easily. 

Conduct a soil test

If the soil lacks nutrients, that may signal low fertility. A soil test will easily confirm nitrogen, potassium, or phosphorus deficiency. These minerals are important for the tree’s growth. The thorough soil profile will help you adjust the best tree fertilizer dosage and application frequency. Adding the required nutrients will boost growth and overall health. 

Fertilizing a newly planted tree

It’s not advisable to use additional fertilizer on young trees. The fertilizer can cause excessive leaf growth and prevent the roots from developing. This may lead to drought stress in the future. You may want to skip using nitrogen fertilizer for new trees. In case you’re using the fertilizer, stick to surface application a month or two after planting. 

Poor tree health

If the tree has yellow or pale green leaves, stunted leaves, and molted patterns of early leaf loss, it indicates poor health. To confirm stunted growth, check the length of the tree and compare it to last year for growth. The large trees grow 4-6 inches/per year. On the other hand, smaller trees grow up to 12 inches. 

Other factors

Apart from soil and tree health, other factors like rainfall and sunlight may also impact the tree and shrub fertilizer needs. 

When to Use Fertilizers?

The best way to decide when to use fertilizer is to time it according to the weather and tree’s needs. 

  • You may start with spring to early summer fertilization and then late summer to early fall application. The needs of the tree at that time of the year will also determine the favorable application. The spring-summer application will ensure the tree has ample nutrients for leaf growth. 
  • If the tree is in good health in spring and summer, you may only fertilize it during the fall season. This is also supported by expert opinion saying the trees reserve nutrients from last year for next spring’s growth. 
  • If the tree is growing actively, it will absorb the fertilizer between new growths. So, it makes sense to add fertilizers by summer and early fall. 
  • On the other hand, fall application is great after the first killing frost for the tree to get back to health. For instance, trees that lose their leaves in fall can start to grow well after the fertilizer application. The excess nutrients may also be stored in roots and help trees develop them further. 
  • Another method is to apply the fertilizer a few times a year instead of just one yearly application. The delivery of nutrients in smaller doses can help the roots absorb better. This method is ideal if the soil is sandy in general and may lose nutrients more quickly over time. Moreover, if the trees and shrubs have multiple growth seasons in a year, the continuous application will help boost the growth.
  • Lastly, avoid fertilizing when the tree is in poor health, as just fertilizing may not fix the tree. Other factors, such as excess water, pests, or damaged roots, may be affecting the trees. Here, a plant tissue analysis may give accurate information. 

Understanding the Fertilizing Needs of Different Trees

Find out about the type of trees to know about their soil requirements. 

Ornamental trees

Ornamental tree fertilizer

Ornamental trees are known for their leaves and twig growth. If you see that the tree’s growth has declined compared to past years, add a nitrogen fertilizer to boost the growth. You may use a high-phosphorus fertilizer to boost flower-growing trees. For treating yellow leaves, add zinc and magnesium-rich fertilizers to the soil.

Evergreen trees

Evergreen trees can benefit from fertilizers with potassium, phosphorus, and nitrogen. Check for dull flowers and needles to adjust the right dosage of evergreen tree fertilizer. 

Hardwood trees

Hardwood trees can have different fertilizer needs depending on their species. If you see the tree growing less than two inches in a year, you may have to fertilize it with a nitrogen, zinc, and iron-containing mix. You can choose a slow-release nitrogen fertilizer for the best effect. 

Fruit trees

The best fruit tree fertilizer will boost the tree’s health to get a high yield. Fruit trees, in general, require more nutrients, such as zinc and nitrogen. You may also add a foliar zinc spray to keep the tree healthy. It’s best to do a soil and plant test to know about the current health and alter fertilizers accordingly. 

Choosing the Right Fertilizers 

Select from organic or inorganic fertilizers as per the tree’s needs. For organic fertilizer, you may go for compost or blood meal and isobutylidene diurea and sulfur-coated urea for inorganic ones. Keep reading as we discuss these in detail. 

Granular fertilizer

Analyzing granular fertilizer will help you pick the right ratio of nutrients, namely nitrogen, phosphorus, and potassium. The fertilizer packaging has three numbers indicating the nitrogen level with the first, phosphorus with the second, and potassium with the third. 

You can decide the ratio based on the current soil health. Since custom mixes may not be available in the market, you can get the closet composition to adjust the soil health. Some common ratios are 10:8:4, 2:1:1, and 10:6:4. Also, look for sulfur, magnesium, and calcium in the fertilizer. 

Slow-release nitrogen 

If your goal is to offer fertilizers in stages, slow-release nitrogen may be the best option. It will not alter the soil health quickly or impact the tree with an overdose of minerals. Plus, you will not have to worry about fertilizing repeatedly. Slow-release fertilizers are also good for the environment as they do not pollute the soil and water.

Organic fertilizers and compost

tree fertilizer Organic fertilizers and compost

Organic fertilizers are excellent when you want to avoid adding chemicals to the soil. You may use blood meal, shredded leaves, cattle manures, kitchen compost, and poultry droppings in the soil. 

Different Methods to Correctly Apply Fertilizer

Here are different methods of applying fertilizers to the trees.

Fertilizing roots

Root area application included adding the fertilizer around twice the diameter of the tree. This will cover the root system that’s under the soil. Cover the turf area with fertilizer so that it will seep into the soil for absorption by the roots. 

You may also apply the fertilizer to roots by applying it 12-15 inches deep if the leaves are not in good health. Add organic compounds such as chopped leaves, shrubs, and bark mulches to ensure the right microbial activity and soil water infiltration. This may take care of the calcium and potassium needs of the soil. 

Surface application

The surface application works well for shrub roots and trees in delivering the right dose of fertilizer. Applying the nitrogen-rich fertilizer to the soil and turf can deliver the mineral to the tree as needed. 

Mark the rectangular area up to six feet beyond the branches of the tree and shrubs to cover all the root zone. If the trees are planted close together, mark the area surrounding the trees to apply the fertilizer. 

Injecting liquid fertilizer 

For this method, a soil needle is used to inject liquid fertilizer below the roots. Make sure each injection is done 3 feet apart for better absorption. This method is ideal for quick delivery of water-soluble fertilizers. 

Hole placement

If the trees are in bad shape with raked leaves, you may use this method as an attempt to save the tree. Dit 6-12 inches deep holes that are two feet apart around the tree trunk. You may extend these up to 6-8 feet to cover the roots below the soil. Evenly divide the fertilizer in these holes. You may add mulch over these holes for additional nutrients. 

Case Studies and Success Stories

Urban Tree Revival

In Seattle, an initiative to revive urban trees involved applying specialized compost blends to improve soil structure. The treatment led to a 30% increase in growth rates among treated maples and elms compared to untreated controls.

Orchard Productivity Boost

A pear orchard in Oregon implemented a customized foliar feed program tailored to the orchard’s specific soil analysis results. This approach boosted fruit yield by 25% and significantly improved fruit firmness and storage life.

Rehabilitation of Coffee Plantations

In Colombia, coffee plantations suffering from nutrient depletion saw remarkable recovery after integrating organic fertilizers with traditional methods. The program not only restored plant health but also increased coffee bean quality, enhancing the plantation’s sustainability and market value.

Parting Words 

When the soil is unable to suffice the requirements of the tree, fertilizers will help keep the growth steady. You may do a soil test or visibly inspect the trees to configure the fertilizer requirement. Signs such as yellow leaves, patchy growth, or a decline in growth may show that trees do not get the right nutrients. 

The best way to determine the tree fertilizer application is to consider the right amount and type of fertilizer and method of application. This will ensure that the tree is adequately fertilized and the roots are able to absorb the needed nutrients. 

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