Deep root fertilization is a recommended procedure by many arborists. Does it work? Is it the best way to fertilize trees? Do trees need to be fertilized?
Deep Root Fertilization – What is it?
Deep root fertilization for trees is a process where you stick a pipe down into the soil about 8-12″ and then, under pressure, squirt fertilizer into the ground. The theory is that since tree roots are deep down in the ground, the fertilizer would also need to be put deeper in the ground. Since this process requires special equipment, it is usually done by an arborist.
It is interesting that the International Society of Arboriculture (ISA) recognizes this as a gardening myth, and yet many ISA certified arborists still sell the service? This is what the ISA says:
“you don’t need to perform “deep root fertilization” to reach their root system-most
of the trees’ fibrous, absorbing roots are in the top eight inches of soil”
A recent review of available literature on tree fertilization in the USA by Daniel K. Struve (ref 1) concluded that “Little difference has been found among fertilizer application methods; broadcast applications are as effective as subsurface applications”.
Note added June 2014: One of the people adding a comment below suggested that deep root fertilization could be done as a DIY (do it yourself) project using a very simple device available from hardware stores. When I first wrote this blog I was only considering the application done by an arborist, which is very expensive. In this situation the original post is still correct. If done as a DIY project, the cost is much less and maybe it is no longer a waste of money. I hope to do a future post looking more closely at DIY deep root fertilization.
Fertilizing Trees
Most fibrous absorbing tree roots are found in the top 2-8″ of soil where water and oxygen are abundant. Fertilizer that is placed below this level does little for the tree and is in fact environmentally harmful.
The key nutrients required by the tree are nitrogen, phosphorus and potassium (NPK). Let’s look at each of these nutrients.
Nitrogen moves through the soil very quickly and is probably the nutrient your tree needs most. An easy way to feed your tree with nitrogen is to just spread it on the ground. It will dissolve in water and flow down to your roots.
Phosphorous does not move through the soil very quickly and so adding it lower down in the soil seems to make sense. However, most soils in North America have plenty of phosphorous in them. Unless a soil test indicates differently, or you know that the soils in your area are phosphorus deficient, you don’t need to add phosphorus.
Potassium moves through the soil relatively quickly, but not as fast as nitrogen. Most healthy clay soils have enough potassium.
Should You Fertilize Your Trees?
If you have healthy soil you probably don’t need to fertilize. The problem in our urban landscapes is that we remove the tree leaves each fall. The leaves are natures way to fertilize the trees and by removing them you are removing the food for future years.
Tree roots that are covered by grass add an additional problem for trees since the grass roots compete with tree roots for nutrients.
In either of these situations it does make sense to feed your trees, but deep root fertilization is a waste of money. Just take normal fertilizer and spread it on the ground. If you are fertilizing your lawn, you are also fertilizing your trees. Let nature move the nutrients to the roots.
References:
- Top Seven Myths of Tree Care, by ISA: http://www.treesaregood.com/searchResults.aspx?q=deep+root&cx=010107291988267817406%3aanhvlksvvbw&cof=FORID%3a9
- A Review of Shade Tree Nitrogen Fertilization Research, by Daniel K. Struve.
- Photo Source: Larry D. Moore
Just read this article…Thanks…saved me some money as the local lawn fert\weed service was trying to push this service x 6 treatments at $69 per treatment for the season! Thought I’d Google it and hit your article.
I did not see any specific fertilizer mix or quantity recommendation though.
How do you determine what kind and how much for each tree is healthy?
In your article you said, ” I hope to do a future post looking more closely at DIY deep root fertilization.”…any chance you did that?
I searched the site but saw no follow up.
Tangent…
I am having issues with several of my trees though that needs some sort of attention…Their bark is getting dark discoloration from the ground working its way up and a couple of them are not looking so vibrant the last 2 yrs…not sure what it is. Also getting progressive fire blight in my pear trees that are supp to be blight resistant…What to do?
Would fertilizing on top at least them help fight?
The only way to know which nutrients are required, and the required amounts is to do a soil test. The soil test will give you this information, except for nitrogen.
I have not done a post of DIY tree fertilizing. The cost is more than spreading the fertilizer, but it is not much higher. If done at the right depth – just below grass roots and above tree roots it is probably effective. I am not convinced it is worth the effort.
Find out the real problem of the trees. then treat the problem. Too many people want to throw something at a problem hoping it will help. Fertilizer is not going cure fire blight, but it might make the tree stronger to help fight the disease. But this is only true if the tree has some nutrient deficiencies which you will only know with a soil test.
Hey, we live in Southern Ontario, too! We live in KW where the soil is quite hard-apcked and rocky due local eskers and moraines, so trees need all the help they can get. This is a great article and we totally agree that people need to be aware of deep root fertilisation but not everyone (or every tree) needs it. Thanks for the great explanation of the importance of NPK.
Actually no tree needs deep root fertilization!
There is a lot of probably in your article. Seems the only thing you are sure of is that deep root fertilizer is a waste of money. You state that if leaves are removed and grass is planted under trees then fertilizer might be needed. I have a tree suffering from severe iron clorosus, what is your solution if fertilizer for trees is a waste of money as you stated.
Ben – you did not read my post. What I said was “In either of these situations (referring to the removal of the leaves)it does make sense to feed your trees, but deep root fertilization is a waste of money. ”
If you have sever chlorosis – you should first get a soil test done. It might be a pH problem, or it could also be a high level of one of the nutrients.
Robert,
Interesting Blog post, however you did not answer your original questions: Does it work? Is it the best way to fertilize trees? Do trees need to be fertilized?
1)Does it work? Deep Root Fertilization does work. But there are many caveats that should be considered before you decide to use it. The important things to remember when choosing to do (or not do) deep root fertilization is what does the soil report say your soil needs and what type of soil do you have (sandy, clay, silts). The soil in Canada is not the same in Alabama, or in Texas. I have never seen a deep root fertilization go deeper than 12 inches (this is the depth we all agree is where the roots of interest are). If you are going any deeper than 12 inches it would be a loss of fertilizer.
There are other reasons to do a DRF:
A)You may need to add something other than the NPK. Many trees (especially fruit and nut) require micro-nutrients to sustain proper fruit production.
B)You can blend your own liquid fertilizer for the actual needs of the tree (based on the soil report), instead of just top dressing with a store bought fertilizer, thereby eliminating waste.
C)The injection of the liquid helps relieve compaction of the soils in the upper 8-10 inches (depending on how deep you go). Think fracking of the soils without the bad consequences of petroleum. The less compacted soils with allow more oxygen into the soil and allow roots to spread more freely. I have used this method successfully to address construction compaction.
D)You can add fungi to boost with mycorrhiza. This method does not top-dress well.
E)Hydrophobic top layer of soil. You may need to break through to get through a hydrophobic layer of leaf matter or something else in the top few inches of soil. Without breaking through this layer the fertilizer would never (or may take a long time) get to the roots.
2)Is it the Best way to fertilize your trees? This depends. It is the quickest. The best (and cheapest) would most likely be an annual top dressing of a slow release product if needed. But whether or not it is the best is dependent on things such as soil type and top cover (lawn, hydrophobic leaf matter, etc.).
3)Do trees need to be fertilized? Trees need nutrients (macro and micro), some or all of these nutrients may be available in the soil. A soil test will tell you if you should fertilize your trees (basically augment the soil). Depending on other factors discussed above DRF may be the best way to do this augmentation.
Using the referenced article from the ISA you stated that the ISA recognizes DRF as a gardening Myth. This is not true, the Myth they state is the shape and depth of the root system. They do say you do not need DRF to reach the roots in top 8 inches of soil and that is true, but what is not stated in this article is this is one of the quickest methods.
So basically DRF should be looked at as a tool in the toolbox of an arborist (or homeowner). Is it the right tool for the job, maybe but there are many considerations. I mean you would not use a hammer to drive in a screw. Is it the cheapest, maybe depending on what you are trying to accomplish. If the soil is nutrient deficient (based on soil report) and no top dressing has been performed for many years the best most affordable option may be to do a DRF. It is far cheaper than replacing a tree.
I would be wary if an Arborist told me I needed a DRF but did not have a soil report for your soil. Also remember that a soil report is time dependent, a 3 year old soil report is not a good representation of what you soil needs.
I think I did answer at least two of the three questions and hinted at the answer to the first one.
Does it work? Provided the fertilizer is applied above the root system, then yes it would work. But if the roots are at 8 inches and the fertilizer is pumped below this, it will have a limited effect.
Re: your points. Yes you should know what fertilizer is needed, this has nothing to do with deep root fertilization. I can blend fertilizer without using the deep root system. Adding fungi does not make sense – the soil already has the mycorrhizal fungi it needs and can support, see: https://www.gardenmyths.com/mycorrhizae-fungi-inoculant-products/.
Does it relieve compaction? Maybe – show me the proof. The service is not sold for this purpose.
Is it the best? It is certainly not the quickest as you claim. I just need to go to the local store, buy some fertilizer, and in an hour I am done. If the ISA does not even recommend it – it can’t be the best option.
A statement like “It is far cheaper than replacing a tree” is silly. It is also cheaper than buying a house – so what. If you have a growing tree, that is established – it will rarely if ever die from lack of fertilization. Even if it needs fertilizer, deep-root fertilization is still not the best solution.
In NW Houston, we have poor soils and tall, slender pines. I fertilize my lawn regularly with top coats. That has caused a mass of roots in the grass that crowds out the grass. I will try root feeding to encourage downward root growth instead of upward growth.
That would be an interesting study. Keep in mind that roots grow where they can get three things; nutrients, water, and air. The top layer will certainly have more air.
As a Practicing Arborist for almost 30 yrs, i disagree. I do however agree with the needle method not being effective. I have been doing deep root fall feedings for many years, but i do the feedings Via soil drench, The feeder roots on all or most plant stock are from 1 inch to 8 inchs within ground surface. Sometimes even blending in with grass roots.This method is very effective, i have nurtured plant stocks back from severe deer damage and insect damage. and as far as all the homeowner do-it-yourselfers, yes it will work, but will never be as effective as the fertilizers an Arborist can purchase… Arborist’s and some like myself DEC licensed applicators should know what formulation your specific plants should need if there in some sort of stress, or lacking a nutrient… using any fertilizer or making your own, may not be effective
good luck, and make it a great day 🙂
V.K.
Long Island New York
By soil drench I assume you mean to apply the fertilizer in liquid form and then washing it in?
No reason why this does not work, provided that the washing in process is done carefully so that there is no run off of fertilizer. However, I would not call this ‘deep root fertilizing’. To get the fertilizer to 8 inches would require a very long slow irrigation process, which can certainly be done, but would not be very practical for a commercial outfit. Each new site would also have to be tested during irrigation to determine the depth to which nutrients are moving.
Nurturing deer damaged trees back to health is best done without fertilizers. The last thing they need is a fertilizer shock. I just leave them alone and they regrow provided they have live dormant buds.
The statement “will never be as effective as the fertilizers an Arborist can purchase” is just wrong. The nitrogen all types of fertilizer needs to be broken down into nitrate or ammonium before plants can use it. Once this is done, plants can’t tell the difference where the molecule came from. To says that arborist fertilizer is better is simply not true. To understand this better have a look at this link https://www.gardenmyths.com/what-is-organic-fertilizer/ Arborists may have a better understanding of which fertilizer to use and when to apply it, but they don’t have special magic fertilizer.
Oh, come now. I have a four-year degree in Forest Management Science, owned a tree and shrub nursery, and have also been licensed for therapeutic treatment of trees with injected fertilizers and pesticides. I know of no restricted fertilizer which is only available to professionals! Wow, there are a lot of pros commenting on here protecting their turf (no horticultural pun intended). Chill out, guys. You are free to sell your wares to those willing to pay you, but all of these replies are sans any scientific evidence showing superior results to what the OP is advising. GOOD ARTICLE, BTW.
After reading a majority of these posts, it is easy to see the one important factor that is being overlooked. At $300 per tree for deep root fertilization, I have to agree, this is highly overpriced and offensive. As a person who provides such services, I will say on average, the first tree is usually $75 and $20 per tree there after. HARDLY A WASTE OF MONEY! If deep root fertilization is recommended, search around for the right price. Do not let yourself overpay.
I have heard from a number of arborists, but you are the first one to provide a reasonable price for the service.
Very expensive???? the cost to feed a mature tree like a 30 inch BHD tree would roughly cost $180, and that is with an organic blend fertilizer. Now if that tree were to die the cost to remove it is in the thousands. if you are lucky and it is close to the road/driveway the damage to grass and landscape may not be bad. But what if it was in the back of your yard, ie no bucket truck, dragging brush across the grass, or even worse running machines across it to take the heavy logs out. That will cost a lot more to restore the area, not to mention the soil compaction and other problems caused by the heavy machines.
Also, have you ever personally fed a tree properly? Are you a licensed Arborist? What kind of fertilizer was applied? What is the history of the site?
There are many questions that come into play, and for someone like you to make a blanket statement that a service is not needed and does not benefit a tree is WRONG. I will also say that there are many people out there who just do the work to make a quick buck, but like any profession there are competent people and others who have no idea.
ISA arborist testing is fairly easy, also some states like NY for example is a joke. I personally passed the open book Pesticide test, without even using my book with a perfect score on the subject and a close to perfect score on the safety in under 20 minutes. People think just because someone has a license they are “professionals” not to mention the people who apply without a license at all.
The reality is that most landscape trees do not need to be fertilized at all. Most soil, at least in North America, contains the nutrients the tree needs. In normal situations trees do not die from lack of nutrients. comparing the cost of the DRF service with removing a dead tree does not make much sense and was not the comparison made in this bog.
I never said that DRF does not benefit the tree. It is a form of fertilizing that works.
I’ve commented before on this topic, and will add a few more comments.
First of all, I notice that some of the comments and responses are confrontational. I believe this results from the tone of the original article – the second sentence states “It’s a waste of money!”. I am not an arborist, just an amateur gardener for many years. Those years result in the benefit of “experience” (not certified expertise), and my experience was that DIY root fertilization seemed beneficial – the comment that it was a waste of money aggravated me enough that I responded. If it aggravated me, I can certainly understand that it would anger those with certification as experts in the field, who recommend the process. Robert, you have the experience and dedication to moderate a blog that provides a valuable source of information and interesting exchange of opinions for all levels of gardeners. My suggestion is that you could benefit from being more open minded, and less dedicated to defending your position, when a comment is challenged. I did not participate in the discussion to participate in a debate, but I found some of your responses to be argumentative rather than constructive.
As for Bret’s comments, in my opinion a number of them seemed valid. In particular, the points on turf competing for the nutrients, and the loss of nutrients [and water] through run-off; I also found the aeration comments to be interesting. I did find Bret’s comments about a DIY approach to be somewhat dismissive, I have yet to engage an arborist to save a tree, but if I did I suppose I would be supporting his argument that he saved another tree that was cared for by a DIY amateur.
None of the comments have convinced me that DIY root feeding [and the use of the $40 root feeder for watering] is a waste of time or money. Storage and time involved are inconsequential, and there is no gas involved. I believe that the small added cost for the fertilizer pellets might be offset by delivering the nutrients without run-off or loss to competing turf. I am sure the DIY gadget does not provide the aeration of a professional high pressure outfit, but I believe it might provide some aeration benefit. If I note a problem with trees, I do spend time on research – usually the articles provided by experts on a university site, that are familiar with my area. The cost of my time is minimal, often just involves ignoring a few commercial breaks during game coverage on T.V.
In summary, I would not hesitate to suggest that amateurs might benefit from DYI root feeders for fertilizing and watering trees. Maybe its like getting back pain relief from a chiropractic visit – some experts might tell you its a waste of time, but you don’t care if its imaginary – you feel better!
Perhaps you viewed an older version of the bog post. I had added the following after another comment about DIY deep root fertilization:
Note added June 2014: One of the people adding a comment below suggested that deep root fertilization could be done as a DIY (do it yourself) project using a very simple device available from hardware stores. When I first wrote this blog I was only considering the application done by an arborist, which is very expensive. In this situation the original post is still correct. If done as a DIY project, the cost is much less and in this case, maybe it is no longer a waste of money. I hope to do a future post looking more closely at DIY deep root fertilization.
The purpose of GardenMyths is to try and understand what we really know about gardening. For the most part the information presented is based on scientific testing. Bert may have some good arguments and he does. You may have had good experiences with the DIY method. Neither of these validate the process. For every gardening myth there are logical arguments why they work, and thousands of people who swear they work. When science finds out they don’t work–it is a myth.
I have found no scientific evidence that supports deep root fertilization. I do have the International society of Arboriculture saying it is a myth.
You make two arguments in favor of deep root fertilization.
1) Eliminate competition with grass. If a lawn grass is growing properly, it will have roots going as deep as the deep root feeding, especially with a DIY tool. You may have reduced competition, but not eliminated it. Besides most people fertilize their lawn as well as their tree.
An arborists tool works under higher pressure and can go deeper. Eliminating competition with grass may be a valid argument here, and it should be fairly easy to test. Fertilize, wait a month, and test the nitrogen levels in the grass. I have not seen such a study.
2) Runoff. Surface runoff is mostly a problem when too much nitrogen is added to the surface of a lawn, followed by heavy rains. This can be a problem. the flip side is that too much nitrogen is injected too deep. The excess still runs away as it moves deeper and sideways in the soil, because roots don’t use it all. You still have runoff of excess fertilizer.
lawn fertilizers go down at a special rate specified for the depth of grass roots and size of areas, one 50lb bag usually covers 10,000 square feet. Therefor, the trees or tree will not get enough of anything Via lawn fertilizers, also if you try to put down too much to try and feed tree, you will burn your lawn. If you soil drench your feedings for your trees and shrubs, the tree feeder roots will absorb the liquid much faster then the lawn roots, especially if the lawn is well irrigated< then make sure your lawn is fertilized at the intervals necessary, you will cut out majority of the competition between the two…. it is science< and timing is everything. Every root system, soil and property have there own characteristics. Its our job to figure out what they need and what to apply.
I don’t agree with some of your comments.
Most lawns are fed more heavily than required, and the excess fertilizer will reach the tree roots. In good soil, grass roots and tree roots are located at about the same level, depending on plant types, and compete with each other. Feeding provides nutrients for both. Putting nitrate on the lawn and watering too much will wash it deep into the soil.
The statement “If you soil drench …the tree feeder roots will absorb the liquid much faster then the lawn roots” is not correct. The rate at which roots absorb nutrients has nothing to do with how the nutrients are applied. Nitrogen is absorbed along with water, and is therefore absorbed at a rate relative to the absorption of water. I do agree that in a liquid formulation, the nutrients are more readily available–but that can be accomplished with a hose as well as deep root feeding. More importantly, most trees are not standing there desperate for a quick feed–they do much better with a slow feed over time. So making the nutrients available more quickly, by adding water, is rarely a requirement of the tree.
Certified Arborist here.. Maybe I can help clear up some of the questions homeowners need consider before DIY projects start. First off, I am a total DIY guy and will take on work outside of my comfort zone when it comes to around the house projects and completely understand the cost savings of DIY.
Here’s the rundown:
1st off – To have a blanket statement of “It’s a waste of money!” is borderline ignorant.
2nd – LOOK at the growing environment of the tree(s). There was very little mention of competing turfgrass, boxwoods, hasta, etc when spreading a surface fertilizer. Turfgrass can take up and absorb a good percentage of the nutrients the TREE needs when this application method is used. Therefore, look at the growing environment! If it makes sense to inject below the competing turf grass then YES, deep root fertilize your trees.
3rd – Deep Root application can be cost effective! Another statement that is completely misleading is “$300 per tree” to fertilize. Here’s something else that hasn’t been mentioned. Multiple trees on site probably have SHARED root space, therefore 1 injection in the same spot can benefit 2 trees, similar to spreading a surface fertilizer.
4th – LOOK at the tree! What’s going on with it? Has the past years weather played a part with it’s decline? Recent construction done around the tree? Are pests causing issues? Does it have a fungus? Why is this important? Because an Arborist can concoct a fertilizer/fungicide mix to help with disease and improve nutrient deficiency. Again, you are injecting this below the completing turfgrass, shrubs when deep root injecting.
5th – Deep root fertilizing breaks up soil compaction because the liquid is injected at a specific PSI. If your soil is compacted, then it doesn’t really matter what type of surface application you use because it will just runoff next rain.
6th – Again, LOOK at the growing environment. If there are streams, water sources, pets in the area, alternative applications need to be considered. Ex. Injection directly into tree.
Final thoughts – Get your soil tested. See what’s missing. Develop a fertilizer with the nutrients (Macro & Micro) that benefits your trees needs. If surface application makes sense then do it. If your tree is surrounded by competing turfgrass DEEP ROOT INJECT. If your tree is declining, there are probably several contributing factors. Arborists have access to much more products and chemicals whether that’s organic or not in feeding your trees and many have been trained in those applications and proper amounts needed for your specific environment.
The last thought – I get called out to help save trees that were previously DIY’d… Not sure if that’s cost effective, but I will tell you most Arborists give free estimates and only get paid for the work performed. Why not get an estimate for the treatment and decide for yourself whether it “Waste’s Money”. DIY’s never factor in gas to store, time spent researching, time spent applying.
This post has generated a number of comments from arborists. they make some of their money selling the service of deep root fertilization so it is no surprise that some of them don’t like the post. In each case I respond to them and ask them for scientific evidence that deep root fertilization works better than surface fertilization. I never get a response and I don’t post their comment.
In this case i decided to post the comment since it does contain more than just a complaint. I sent the Bbowman an email and asked 2 questions:
1) can he provide scientific evidence that deep root fertilization works better than surface fertilization.
2) what does he charge for the service for a mature sugar maple tree. Obviously he feels $300 is “completely misleading”.
I got no response.
Since none of the arborists that contacted me have been able to provide the scientific evidence requested, we have to conclude they don’t have it. Which helps to confirms that the information presented in the original post was correct.
Since Bbowman was not willing to provide his price for the service I can only conclude that $300 is a reasonable price, or maybe it is too low–the price quote of $300 is quite a few years old now.
The above comment does make an interesting point about aerating the soil when deep root fertilization is done. Makes sense, since they use significant pressure. I have not been able to find any confirmation that deep root fertilization has a significant effect on compaction.
I also want to point out that i never said arborist services were not valuable. My original post only looked at one specific service they provided.
Why dont you provide scientific evidence that it DOESNT work better than surface fertilization?
Why? The society that represents arborist have already done the research work for me, and have stated the procedure does not work. If they don’t believe the procedure works, and they support the industry promoting ways for arborists to sell services, why would anyone question it?
I’ve had many people question my comments – not one has produced a single research paper in support of the practice. If you send me one I will gladly post it on my site.
Robert,
I live in Northeast Ohio, four years ago I planted a dawn redwood tree and it was doing great until this spring. We had a late frost just as the leaves where coming out. The top portion of the tree has curled and the needles have fallen off. The bottom portion still has the needles they have not grown any more are green. I was looking into the deep root feeding to try and bring the tree back. Do you have any suggestions? I used weed and feed on the lawn and was wondering if this could have caused the problem.
When a tree suddenly does not do well you first have to look at the things that have changed. They might be causing the problem. The winter in many parts of the country was very cold this year. It might have killed the top buds. A lot of trees and shrubs were damaged this year.
It is unlikely that a disease or pest has caused such a sudden problem, and I don’t know of any that prevent bud break in spring. Nutrients are not likely the problem. Except for nitrogen the nutrient levels do not change that quickly.
It is very common for people to reach for fertilizer when a plant is doing poorly. This is rarely a good idea. Before you fertilize, have the soil tested to make sure this is the problem. Adding excess fertilizer when the tree has a different problem can only make matters worse.
I don’t think weed and feed on the lawn would be the problem. Almost all residential lawns contain tree roots, and if the pesticide in weed and feed were killing trees it would be a big problem for everyone.