A write up I did about tree health and fertilization


New Member
It was well received at the company I work for and estimators pushed fertilization a bit more.

Trees and turf grass competition in the urban environment

Research indicates that turf grass significantly reduces tree root development. Kentucky bluegrass is the predominant turf grass because the dense roots and rhizomes make it ideal to cut into sod. Trees fine absorbing roots have difficulty competing with the dense bluegrass roots in the upper portions of soil, where oxygen content and moisture level is the highest. Poor aeration and drainage of clay soil also inhibits the growth of fine absorbing roots in deeper soil layers. A tree with a poorly developed root system has a reduced ability to absorb moisture and nutrients from the soil. Field studies indicate that trunk diameter and height growth is reduced in trees grown in turf grass than trees grown in bare soil or mulch. Leaf canopy is also noticeably thinner in trees grown in turf.


Whenever possible, mulch the area beneath the tree canopy with a 3-4” layer of wood mulch. A field study at the Morton Arboretum in Lisle, Illinois, showed that after only two months, elimination of grass around 20-year old trees resulted in a 113% increase in fine root density in sugar maples, and increases of over 30% in green ash and little leaf lindens.


The addition of tree fertilizer can reduce the negative effects on tree roots from turf grass competition. One study I found showed an immediate increase in fine absorbing roots after fertilization and an increase of 50% 2 years after the initial fertilization versus the control group with no fertilization.

Tree Fertilization supplies nitrogen, phosphorus and potassium, the 3 macronutrients needed in the greatest quantity. The most noticeable result of fertilization is an increase in the growth and vigor of young trees. It also enhances the green color of leaves and needles, but it’s more noticeable on smaller trees and shrubs.

Answers to some common questions

Q- Can tree fertilization reverse decline?

A- A light amount of fertilizer may help a tree in decline but if too much nitrogen is given it can actually make things worse. High amounts of nitrogen might stimulate new growth causing the tree to deplete its energy reserve. Making the tree unable to leaf out the following year.

In the case of high value declining trees, cambistat (paclobutrazol) would be our best bet to preserve the tree. Fertilization the following year should be okay if tree looks to be improving.

Q-Does fertilization treat chlorosis of leaves?

A- No, the underlying cause of chlorosis needs to be addressed to see improvement. This would include a sulfur app to reduce soil ph in small trees with minor chlorosis, or trunk injection of micronutrients in trees with moderate to severe chlorosis.

Once the underlying micronutrient deficiency has been addressed fertilization can be utilized to promote and maintain health.

Q-What trees benefit from fertilization the most?

A- Small to medium sized tree in reasonably good health benefit the most from an annual fertilizer program. Mature trees also benefit but it’s less noticeable than the smaller trees.

I would like estimators to focus on more multi tree fert jobs with small to medium size trees. It seemed to me the majority of our jobs in 2014 were single tree jobs and it felt like we were just spinning our wheels on all these small jobs. Nearly every home has a few small-med trees that will benefit and we should try to get more of these jobs.

Q-Do trees need to be fertilized every year?

A- In most cases yes, fertilizing is recommended every year. According to Davey’s website (our fertilizer manufacturer) annual fertilization with Davey Arbor Green Pro has a cumulative “soil rebuilding” effect and the amount of slow release nitrogen in the soil increases over multiple years (I have a Davey fertilizer slideshow on my laptop if anyone is interested in watching).

The only exceptions to annual fertilization would be trees growing in a limited space where homeowners may not wish them to grow faster. Pines with Schaeropsis needle blight shouldn’t be fertilized since nitrogen has been shown to worsen the disease. Trees growing in wooded settings or volunteer trees would be low on our list but can be fertilized if homeowner insists.

Q-My lawn company fertilizes trees for less

A- Here are some comparisons between our fertilizer and theirs -

Lawn company-

Quick release water soluble fertilizer mixes easily in tank with water

Short lasting, multiple applications required per year

High salt content can cause burn

High risk of runoff in rain

Sprayed over top of lawn where turf grass gets the most benefit before reaching tree roots

Tree company-

66% of nitrogen is slow release non water soluble, requires a tank mixer to keep suspended

Long lasting, 1 application per year

Microbial release of nitrogen very similar to release of organic fertilizer (manure/compost)

Low salt content will not cause burn

Little risk of runoff in rain

Fertilizer is injected 4-6 inches into ground, where tree roots get the most benefit

High pressure injection loosens and aerates soil

Source citations

Trees and turf: are they compatible


Soil test interpretations and fertilizer management for lawns, turf, gardens and landscape plants


Root growth response to fertilizers


Tree decline



New Member
United States
The most neglected tree service, yet the most important. Everything needs to eat, trees are no different. Tree spikes are analogous to snicker bars and turf fertilizer is like sugar, pushes growth. Arbor Green and similar slow release fertilizers made for trees are like 7 course meals, feeds the entire tree, roots, trunk, branches etc... Strong, healthy and resilient is the goal.


Well-Known Member
Add a tissue test at the same time and use them together. Another test that isn't run very often is for lime. You can infer high lime based on Ca, CEC, and pH but it's a guesstimate . Your basic soil test doesn't always tell all you need.

Also don't forget the physical aspect of the soil!

I love it when you talk dirty to me.


Well-Known Member
Ontario, Canada
Applaud your courage to post this here.
Truthly we would give you a failing grade.
Fertilize is the last option in most every case.
Liquid injection is a waste of non-renewable resources
It is a misleading and dishonest to fertilize without proper tree and soil analysis.
Many reasons for slow growing and nutrient deficient trees and assuming fertilizing is the answer shows ignorance and allows a competitor to easily sell their service vs your dishonesty.


Well-Known Member
The thing about fertilizer is it’s an easy concept for average homeowners to understand and the fertilizer company have advertised whether it be for lawns etc the base theory is still the same so it’s an easy topic to sell.

I absolutely have no issue with augmenting soil to be honest a lot of town home builds, condos and especially newer houses I’ve worked on can hav crap for soil.

The catch is fertilizing is quick,easy and cost effective and makes people feel like there I’ve taken care of that check it off the list.

The cost is a big issue I come across trying to sell below grade work. People can se bigger greener leaves, they can see deadwood, they can see house clearance being needed.
But they don’t understand what they don’t see and look around trees grow everywhere roots and dirt they’re good to go they’ve done it for a million years.

When it comes to care trees are like onions they have layers. If you target 1 issue and not the big picture I don’t think I’d call you dishonest. So many times I can talk to people and inform them on a-z that we could do for their tree but if they don’t want or have it click or it’s not on there list or it’s too much $ it doesn’t matter. If you’re targeting a legitimate issue and you do so in an agreed way on an agreed scope on an agreed fee I won’t call that dishonest.
On that note not every arborist knows the same thing and they may not offer services outside their wheelhouse and that’s ok.

I’ve seen struggling Norway maples come back and replenish for a few years and it made the customers happy to get a few more years out of them. The girdling root causing the issue wasn’t dealt with being outside offered services and the homeowner was happy. Is anyone in the wrong there??

My thoughts aside I have a question about that article.
One study I found showed an immediate increase in fine absorbing roots after fertilization and an increase of 50% 2 years after the initial fertilization versus the control group with no fertilization.

This is an interesting tidbit but I’m wondering if there’s any tunnel vision here? It’s a fertilizer study so the results were attributed to the fertilizer. However, tree roots and branches work on similar principles. For example if you remove a competing neighbouring tree and it releases the subject tree growth in the released area will be noticeable.
With this root study the forced water pressure loosens the surrounding soil area more or less a hydro version of aeration. With the newly found ease of growth in the spacious area is the tree just being efficient and taking advantage of the opportunity.
Also, on that note how much of that is a natural rooting defence? We all know when soil gets over saturated we get calls for newly horizontal spruce. So if this happens in kind of a micro soil climate scale does the tree worry about the lack of soil stability and send out fine roots to cling for survival?

In the end I like and thank you for sharing that right up but sometimes I wonder about tunnel vision on education.

But please keep sharing these chats are the best spot possible to learn

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