A science-based tree fertilization question

I was thinking about fertilization in trees today, and I would like to pose a question to those arborists here with greater knowledge than myself.

It is well understood that fertilization of lawns promotes excess top growth, and pre-disposes the turf to some diseases, certainly to increased insect invasion by grubworms. Certainly, the trees growing in heavily fertilized yards are also heavily fertilized.

I would theorize that trees growing in a heavily fertilized lawn grow faster, have less dense wood as a result, and are consequently more prone to storm and ice damage. I suspect that these trees may also be more likely to get some fungal diseases, although I doubt the insect problems are any more prevalent in over-fertilized trees.

Are there any studies that show that heavily fertilized trees have more structural problems than their woodland cousins?
I would like to hear anyone's opinions on the topic as well.

I don't really have any way to assess this question on my own for the following reasons:
1. The relative frequency of calls in fertilized or non-fertilized lawn will be meaningless. The people that really care about their yards and do the extra fertilization are also the same customers that call first for tree trimming and to repair storm damage. Conversely, the people that ignore their yards tend to ignore the trees, so the "amount" of tree work in the two different types of lawn could not be evaluated based on the number of calls from each type of yard.
2. When I show up on an over-fertilized yard (deep green, lush dense growth, perfect appearance), I usually have no way of knowing how long that tree has been over fertilized.
3. Unless I am doing soil tests, "over fertilized" would be entirely subjective.
4. Storm damage is so localized, there would almost never be a way to assess the damage from one yard to the next. Hmm... Ice storm damage is pretty consistent...

An after thought...

It also occurs to me that many arborists are in the business of selling tree fertilization, and this is not the sort of thing that the tree care industry would be inclined to look for or report.

I suspect the research has been done although I don't know where to find it. If I was going to research this issue, I would use street trees. The soils are going to be fairly consistent, as will microclimates. By alternating fertilized trees and not fertilized trees, you will have a control. You can then test changes in growth, wood density and over time other effects such as fungal problems and limb failure.

Very little of the nutrients (primarily nitrogen) in grass fertilizer gets through the turf, so a heavily fertilized grass doesn't necessarily mean the trees are heavily fertilized.

I know there are long term forestry fertilization trials and I'm sure Davey has some trials going on related to the use of their Arborgreen.

First place to look would be the Journal of Arboriculture.

Have fun.

I genuinely believe that your statement "Very little of the nutrients (primarily nitrogen) in grass fertilizer gets through the turf, so a heavily fertilized grass doesn't necessarily mean the trees are heavily fertilized" is mistaken. This is a commonly held belief by most "tree people" that I have been trying for some time to dispel. Curiously, the lawn people are equally convinced that the trees are getting all the fertilizer. So far, I am not aware of any scientific sources to prove whether trees or lawn gets the most out of the fertilizers we apply. I think it is the trees:

1. Tree roots are everywhere the lawn roots are. Dig in the soil anywhere under a tree where the lawn is and see for yourself. It is heavily laced with tree roots, both deep and shallow. Trees and grass are fighting on the same battlefield.

2. Look at the lawn underneath most trees. It is thinner, less green, and grows slower.

3. I have successfully grown grass in the bare areas underneath trees by doing nothing more than increase the fertilization in that area. The trees get more of the soil nutrients (and water) than the lawn does, so the grass dies out unless it is supplemented. I would include sunlight in this argument, but I have trimmed trees to increase sunlight to the lawn. Without supplementing the fertilization, nothing usually changes.

4. Groundwater contamination by nitrogen fertilizers is a pretty strong indication that the nitrogen is not staying in the top 2 inches of the soil. Unless I am sadly mistaken about soil chemistry, there is very little adsorption by the soil of either ammoniacal, nitrate nitrogen, or the urea based soluble sources. Hence, the algal blooms causing ecological attention in streams, rivers, and eventually the ocean. (BTW, the same is true of most forms of potash & phosphorus) Here is a pretty good article on this topic for agricultural fertilization: http://www.ag.ndsu.edu/pubs/plantsci/soilfert/eb64w.htm



Of course, I am open to any comments on the topic of trees vs. lawn as well.

Keep in mind that I have been a lawn professional much longer than I have been an arborist, so my observations are based on a different perspective than most of the folks here at ArboristSite.

Not sure if I can answer your question the way you asked it - but can offer some kind of answer.

After years at country clubs, and far more years in the residential areas, I concluded that some of the best condition trees were ones not part of fertilizer programs - for the trees.

As far as turf - if the grass was not over-fertilized, I think the sod would have utilized much of the extra nutrients before excess made it's way into the trees.

Sometimes turf fertilizer is applied foliar, and that is different from broadcasting granules.

I strongly take issue with any assertion that trees get most of the nutrients from a fertilizer applied to a lush lawn. From my experience and recommendations based on ANSI standards, a lawn can out-compete trees for water and nutrients due to their higher density of absorbing root hairs per unit area. To explain: Quite often we are called on to come out and evaluate a tree that is doing poorly in a "well cared for" landscape. Before I even visit the site I know what I'll find: A lush lawn that is growing right up to the base of the tree that is doing badly. Time and time again, we break out the shooters and picks and carefully scalp the lawn back about four feet from the tree. Then we swale and berm with a good organic mulch and in 3-6 months---Bingo! The tree is looking good and thriving. The reason: The lush lawn was soaking up all water and nutrients around the tree's base sending it into a serious water/nutrient deprivation downward mortality spiral. When we scalp the lawn and apply the mulch the tree can then get far more water and nutrients from its surrounding base area. As for fertilization: It's mostly a scam. There are specific cases where trees have been installed in construction fill that is nutrient deficient where fertilizer will help, but research has shown that fertilization without rigorous soil testing can lead a tree into channeling its energies into growth at the peril of taking energy away from defense. Oportunistic pathogens then attack and it's bad news for the tree. Most absurd is the habit of some municipalities that force developers to fertilize naturally sited trees around their sites before breaking ground for any and all projects, without any soil testing, whatsoever. Trees growing wild, on their own, in nature, have long ago made their peace with their environment's nutrient profile. To blanket fertilize such trees is insanity.

Sunrise Guy said:

I strongly take issue with any assertion that trees get most of the nutrients from a fertilizer applied to a lush lawn. From my experience and recommendations based on ANSI standards, a lawn can out-compete trees for water and nutrients due to their higher density of absorbing root hairs per unit area. To explain: Quite often we are called on to come out and evaluate a tree that is doing poorly in a "well cared for" landscape. Before I even visit the site I know what I'll find: A lush lawn that is growing right up to the base of the tree that is doing badly. Time and time again, we break out the shooters and picks and carefully scalp the lawn back about four feet from the tree. Then we swale and berm with a good organic mulch and in 3-6 months---Bingo! The tree is looking good and thriving. The reason: The lush lawn was soaking up all water and nutrients around the tree's base sending it into a serious water/nutrient deprivation downward mortality spiral. When we scalp the lawn and apply the mulch the tree can then get far more water and nutrients from its surrounding base area. As for fertilization: It's mostly a scam. There are specific cases where trees have been installed in construction fill that is nutrient deficient where fertilizer will help, but research has shown that fertilization without rigorous soil testing can lead a tree into channeling its energies into growth at the peril of taking energy away from defense. Oportunistic pathogens then attack and it's bad news for the tree. Most absurd is the habit of some municipalities that force developers to fertilize naturally sited trees around their sites before breaking ground for any and all projects, without any soil testing, whatsoever. Trees growing wild, on their own, in nature, have long ago made their peace with their environment's nutrient profile. To blanket fertilize such trees is insanity.

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Sunrise,

I don't "Do" trees, I do bushes. Blueberrys, and many thousands of them in rows. I agree whole heartedly with your observations on nutrient and water competition from ground cover.

There is a growing debate over clean tilled rows versus ground covered rows in the name of soil conservation, and the use of overhead vs. trickle irrigation.

When studied using leaf analysis it was shown that with clean tilled rows(no ground cover) fertilization could be cut back almost in half, and more so if if tilling folowed application to reduce nitrogen loss.

Overhead irrigation was studied and the results were very interesting.
Darn near triple the amount of water was required on rows with ground cover.
Trickle irrigation again proved to be the most effective in getting water to the roots, but unfortunately it is a PITA.

I can see where with tree's and lawns, the same holds true if not more so.

Stay safe!
Dingeryote

Even forest trees can be over fertilized. The Costal Doug-firs get a lot more nitrogen then other Doug-firs since they live alongside the nitrogen fixing red alder. Their higher occurrence of swiss-needle cast is attributed to the hire nitrogen in the foliage.

Not only fertilizing the tree, but the fungus that lives on the tree. Crazy huh?

Not crazy, it makes sense to me.

But are there problems associated with the higher nitrogen?


Nitrogen fixing alder? I thought only legumes (beans and the like) were capable of fixing nitrogen.

pdqdl said:

Not crazy, it makes sense to me.

But are there problems associated with the higher nitrogen?


Nitrogen fixing alder? I thought only legumes (beans and the like) were capable of fixing nitrogen.

Click to expand...

Acacia trees also nitrogen fix.

Stay safe!
Dingeryote

Nitrogen fixing trees

I did some research. Learned some new stuff.

Acacia are legumes, being in the family Fabaceae. No surprise there. Thorns, bean pods, they have all the signs.

Alder go into a completely different class of plants: they are associated with a different group of nitrogen fixing bacteria called actinomycetes. As such, they still get the job done without being legumes.

There is a third group of nitrogen fixing bacteria: Cyanobacteria, but the plants associated with them don't seem to be trees.


Back to the original question: excess nitrogen and tree health. Comments?

Ha! I was all ready to comment on this one and Sunrise beat me to it. On point!

pdpql if your perspective is heavily influenced from years or lawn service you must realize absorbing root denisty per square inch of sod versus the absorbing root denisty per square inch of tree, generally speaking. Without beating a dead horse sod most definitely wins that battle and I would have to disagree they're on the same playing ground for that very reason. Even more so because sod catches the water first. I too 'relieve' tree roots of invasive sod if not only for increased water but also to keep landscapers from whipping and crashing the hell out of the trunks. The area is replaced with a nice 2-3 inch layer of wood chip (not bark) mulch which we all know provides numerous benefits. Berm it on a slope to help capture surface water for the absorbing roots...which are rarely very deep unless there's water for them to chase...just not enough oxygen way down there. Dingeryote's overhead irrigation study illustrates this well.

As certified arborists we all learned about 'fertilization by prescription'. Again not to repeat what's already been said but in the typical well kept lawn with plush green grass and happy trees I never sell inorganic fertilization services. At most we will peel back sod and provide the tree with good ol', organic, wood chip mulch which will slowly break down over time and help to maintain what are likely already sufficient soil nitrogen levels. Blanket fertilization poisons drinking water, to be blunt.

Soil texture does play a part in all of this. I recently helped a couple revive a dying smoke tree that was planted in silty sand. By amending the soil with organic compost and incorporating a much needed, one-time application of inorganic, fast-release fertilizer, the tree looks wonderful this Spring and the occurance of deadwood has virtually ceased.

Journal of Arboriculture would definitely have the scientific research you're looking for, I've physically read it there. Sorry I'm still too lame to dig it up and post it right now.

Great topic!

N is very mobile in the soil, I think both Pirrone's book and Harris' "Arboriculture" mention that lawn fert will give adequate N to a tree. This said, I think they get too much N from lawn fert, and not enough minor and micro nutrients due to loss of nutrient cycling in urban environments.

Wood much will help with this, as long as we start with a composted component

Many of the above posts are mixing H2O deficiency and fert, with water being the biggest limiting factor to establishment and growth irrigation has to be addressed before anything else can be done.

There are so many other practices that can be done, such as using deep rooting perennials to assist with perk and gas exchange. We so often forget that there are associate and associative organisms that the tree needs to thrive.

How about a few scoops of worm castings in with the mulch compost? Heck, add some native worms too!

TheRick said:

Their higher occurrence of swiss-needle cast is attributed to the hire nitrogen in the foliage.

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pdqdl said:

But are there problems associated with the higher nitrogen?

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Most definitely. One study by UW Madison showed a 300% increase of tent catipillars on fert'ed trees vs untreated. It was a same site study. It will take a while for me to find it, if I have time, I first saw it over 10 years ago. It was one of the things that shifted me away from ChemLawn.

Anther one, i think i heard this in a Kim Coder lecture, was one of that major timber holders "up nort there" thought that they could use paper sludge as an amendment. Pine stands started showing a huge increase in needle blight, and the only differance was that the treated stands had the bight, and a slightly elevated foliar N, where the untreated stands were normal.

Another showed that sucking insects are found in higher populations on trees exposed to higher N. Sucking insects secrete carbohydrates because they are looking for the less abundant N compounds.

Running late for school, maybe more later

GReat thread!!!

During my time back at College in 2005, fertilizing trees came up as a topic.
I dragged out my notes and here is some of what I wrote:

Root Feeding
NPK - trees most likely will uptake N in preferance to other nitrients - you can actually cause a nutrient deficiency - with uptake of N you get a lot of leaf growth, high in soft elements, not a lot of lignin - yummy for bugs.

Fork and Compost
Can't beat it, feeds soil organisms, encourages earthworms, supports the rhizosphere.

When a tree is sickly it tends to shut things down, reduce growth, small leaf size - it does not use up stored energy reserves - Mass:energy ratio.
Application of fertilizers and selective uptake of N bypasses that process - tree responds by flushing growth - can actually do more harm to a 'sickly' tree by totally upsetting the mass:energy ration.

Soil Tests
Are good for checking the site with an idea of planting species that are suitable for that site NOT for developing any kind of fertilization plan. Careful consideration must be given to the CAUSE of the deficiency and the effects of fertilization - N flushing upsets mass:energy ratio.
Deficiency may be caused by a lack of a specific element or the lack of availability of element to the tree due to pH.

Applications when planting, trees may benefit from phosphorus but not NPK granules, trees show element status of the lifting site for 2-3 years. During this time the tree lives on potential energy.

Fertilization, often called 'tree feeding'. TO use this term indicates a poor understanding of how a tree takes up elements. Elements are taken up from the soil carried in water by the process of diffusion, also there is selective uptake, plants can take up elements selectively, not necessarily to its own benefit.

Diagnosis and Fertilization
Leaf analysis can be informative about actual elements that are reaching the leaves - take leaves from lower, middle and upper crown.
Starch tests can provide evidence on the reason for low vitality in trees
meters on leaves can measure chlorophyll concentrations
Mulching (composted leaf litter / wood chips) retaines moderated temperature, moisture, slow supply of elements, aeration and encourages soil organisms...trees have evolved with mulching.

TheRick said:

Even forest trees can be over fertilized. The Costal Doug-firs get a lot more nitrogen then other Doug-firs since they live alongside the nitrogen fixing red alder. Their higher occurrence of swiss-needle cast is attributed to the hire nitrogen in the foliage.

Not only fertilizing the tree, but the fungus that lives on the tree. Crazy huh?

Click to expand...

That's an interesting point.

Now you have me wanting to stop along Highway 26 on the way to Seaside next time I drive. There are several steams lined with alder. Might be a fun leg stretch to wander down and check out the evergreens that parallel them.

THANK YOU BERMIE! That is what I was asking about!

Bermie said:

GReat thread!!!

During my time back at College in 2005, fertilizing trees came up as a topic.
I dragged out my notes and here is some of what I wrote:

Root Feeding
NPK - trees most likely will uptake N in preferance to other nitrients - you can actually cause a nutrient deficiency - with uptake of N you get a lot of leaf growth, high in soft elements, not a lot of lignin - yummy for bugs.

...[parts deleted for brevity]

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The part about reduced lignin should translate to weaker structure and more storm damage.

Perhaps someone else will pipe in with more good info?

pdqdl said:

THANK YOU BERMIE!
The part about reduced lignin should translate to weaker structure and more storm damage.

Click to expand...

I think this is a smaller issue compared to the increases risk for (suseptability is not in my spell-check) insect and disease problems.

The flush of growth is short term, trees will optimize with wind loading, ie add girth at moment of bend.

I am glad that you are taking an interest though.

dingeryote said:

There is a growing debate over clean tilled rows versus ground covered rows in the name of soil conservation, and the use of overhead vs. trickle irrigation.

When studied using leaf analysis it was shown that with clean tilled rows(no ground cover) fertilization could be cut back almost in half, and more so if if tilling folowed application to reduce nitrogen loss.
Dingeryote

Click to expand...

Not sure I'm following what you mean ? Is this for plowed rows the first year they're planted or are the rows tilled for weed control a couple times a year?
Covered I guess with a weed fabric in between rows?

John Paul Sanborn said:

I think this is a smaller issue compared to the increases risk for (suseptability is not in my spell-check) insect and disease problems.

The flush of growth is short term, trees will optimize with wind loading, ie add girth at moment of bend.

I am glad that you are taking an interest though.

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I agree, JPS, a smaller issue indeed. But isn't it worth considering, given the number of threads on this site from tree services seeking to learn more about fertilizing trees? ($ Ka-Ching ! $) If there is evidence to show customers that they should NOT fertilize the trees in addition to the lawn, year after year, shouldn't we have that as a well known fact, rather than a suspicion passed around by only the arboricultural elite?

Back on topic:

Flush of growth IS short term, unless it is in a yard with a long term high fertility growth pattern. Then it happens year after year. This is exactly what I am thinking about: the long term effects on a tree, from sapling to maturity of growing in a highly fertile environment, and consequently having diminished strength as a result.

We have all seen that the good growth years have wider distance between the growth rings, and poor years are more compressed. If all the growth rings are wide (more soft tissue), if the internodal distances are greater, and the lignin content is reduced, wouldn't that translate to a measurable reduction in resistance to storm damage?

Is there any mechanism for trees to strengthen the secondary xylem after it has been grown? Sorry! I simply don't know the answer to that. Perhaps if I knew more of the cell biology of plants I would not be dwelling on this topic. All the subject material I have read dwells on cambium, phloem, vascular tissue, etc. Not much information available on what happens to the xylem cells once they are grown.

So many variables, so hard to evaluate. I think all the easier to measure problems have been looked into: disease resistance, insect infestation, etc.

pdqdl said:

THANK YOU BERMIE! That is what I was asking about!





The part about reduced lignin should translate to weaker structure and more storm damage.

Perhaps someone else will pipe in with more good info?

Click to expand...

Now, that note I wrote was in relation to established trees, where 'sickly' or 'languishing' trees were being prescribed fertilization as a treatment. With the application of an N base fertilizer, flushing of soft growth, using stored starch reserves would lead to susceptibility (check that JPS!) to insect infestation, and upsetting of the mass;energy ratio, to the ultimate detriment of the tree. Reduced energy reserves, insect/fungal attack so therefore an increased spiral downwards in vitality and overall health, QUITE the opposite of what is originally intended.
And as PDQL was saying, there seems to be an increase in questions relation to fertilizing, that if the folks don't understand the whole issue from soil rhizosphere to twig tips then more harm than good can ultimately result...