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
I never knew that the most fibrous tree roots are found in the top 2-8″ of soil because oxygen and water are most abundant! My husband and I want to start a small orchard/vineyard, and we want to ensure our plants are in optimum condition. We’ll have to look more into sub-surface fertilization systems. Thanks for the information!
Jim please review this sp548.pdf the answers will come to you. There hundreds of these documents on the internet just waiting to be explored. Just put SP548.pdf into Google and it will come to you!
Jim, give me few to site my statement.
To Jim, so many things wrong with your response I don’t really know where to begin. 1. ANSI A300 Series states broad casting fertilizer over deep root feeding is the preferred method. If you injected your fertilizer at a depth of 5″ you would bypass 90% of the feeder roots. An understanding of tree physiology would explain the problem with this.
Maybe the disconnect here is in the name of your company. Maybe your just to busy landscaping to understand tree physiology. Whatever the case you shouldn’t comment on things that you don’t fully understand. Because when you do, you add to the problem of the myth.
To Eric Putnam, You are dead wrong and I don’t understand why you’re referring to ANSI Standards without actually reading them.
ANSI A300 series Part 2, section 18.6.1.1 states that the preferred method of fertilization is soil injection to a depth of 4 to 8 inches with liquid slow release fertilizer. When done properly that’s exactly what deep root feeding with a liquid injector does. I have removed entire residential yards with a sod cutter down 2 to 3 inches and and there’s very few feeder roots at that level. I’ve also increased the size of tree rings around hundreds of trees by removing sod and again very few feeder roots.Furthermore the location of feeder roots varies depending on the tree. Anyone with any practical experience who’s actually stuck a shovel in the ground or done root injections knows you’re wrong. You are the one that lacks a full understanding.
Also, I don’t know how you would know the name of my company when it hasn’t been included in any of my comments. It’s only in my email and this site says that email addresses are never made public.
The email was not released by me.
ANSI A300 Part 2 states section 15.7.4.1 Where turf,mulch, or ground covers exist, subsurface fertilization should be the preferred method of fertilization.
ANSI A 300 Part 2 Section 15.7.6.3 Injection site spacing and depth shall be specified. Injection sites should be 12 to 36 inches apart and 4 to 8 inches deep, not to exceed 12 inches deep.
That kids is straight from the ANSI 300. the problem is that very deep fertilization will miss the sweet zone of root depth. Most arborists I know now refer to liquid root feeding as root zone feeding. Turf grass is a huge consumer of nitrogen and if you just spread fert on the surface very little N will get to the tree.
Disagree with “if you just spread fert on the surface very little N will get to the tree”. Grass roots and tree roots will occupy a similar root zone and compete for nitrogen. The added nitrogen is not used up in a day or two, and excess runs deeper with each rain or watering.
I own a lawn and landscape company in the Kansas City area. I am licensed and certified for turf and ornamental fertilizer and pesticide applications. I disagree with most of your article on deep root feeding.
As a professional who charges for his services, deep root feeding is the quickest and most economical way to fertilize trees. It is also the best and most effective way to fertilize.
– I am not aware of any deep root feeding equipment that injects deeper than about 6 inches. My root feeder has a 5″ deep injector and it is the most common on the market today.
– I mainly use deep root feeding on large commercial projects where hundreds of new trees have been planted. My largest account has 500 new trees planted by my company over the last 3 years. There’s no faster, better or more economical way to get needed (yes needed) fertilizer, micronutrients and michorhiza to those trees.
– Your comment that it is not necessary to add mycorrhiza when planting new trees is totally inaccurate. It greatly increases survival rate. I’ve done tests comparing the root systems of trees and shrubs that had mycorrhiza injected after planting vs. those that didn’t and there is no comparison.The same applies to fertilizing vs. not fertilizing. Deep root feeding also gives me the option of injecting nutrients directly into the root ball of the tree quickly and easily. And no I’m not going to burn the roots because I know what I’m doing as far as the correct formulation.
– If you use granular fertilizer around the base of a tree you are also fertilizing the turf at the same time and then that turf area will be greener and grow faster than the rest of the turf on the property. To most people that’s unsightly.
In sum, if I used your method of fertilizing I would have a much lower survival rate, spend twice as much time for poor results and have unhappy customers. This is based on 30 years of experience. I have tried it both ways and deep root feeding is the far superior method.
This is a myth because people believe it – especially people in the industry selling the services.
Would be happy to review any data you have to support your belief.
Wow. I was searching google for information about fertilising, and learned a lot. I have tree roots in places above ground, and your “hardpan” answer is most likely correct. The place I have lived for almost 42 years now, back in the 60’s about 15 feet of soil was removed over a two acre parcel and used to provide fill (330 thousand cu yards or some such huge amount) for a causeway into the local town.
But the reaction to deep root fertilisation by arborists is stunning. And criticism of your saying its a “waste of money” as being confrontational? Give me a break! Nothing wrong with calling a spade a spade, and reading the information provided from both the defenders and the offenders makes it clear to me that you are right.
But folks do waste money often. On many things
Mr Pavlis, thank you for your blog, and speaking your mind.
Thank you Robert. I wish you lived here in AZ. Our soil, etc., is so different than Canada’s is however I think there is a general common sense that I can take with me from your info. Thanks and Take Good Care!
Sir give me answer how much time take an apple tree to absorb fertilizer from root to fruit
I don’t know, but would think it is hours, not days, since it will travel up the plant with the water. It will also depend on which nutrient it is.
I’m so glad we have people like you who have experience use common sense sprinkled with science to educate and entertain us. I started my Gan Eden approx. 14 years ago (no experience) but and have been trying to figure out if I’ve neglected my trees and shrubs by not feeding them all these years and if I should give them a boost now. Every site visited had different advice and often conflicting advice. And with so many species I wondered if one size fit all or if they each needed to be treated individually. And then there was the fact I have so many different plants growing under them, miniature ferns, hosta, astilbe Now adding bulbs, different flowers (most of what I plant are miniatures or dwarf) to name a few and now starting a moss garden. My main concern is how to fertilize w/out bothering my plants. I also plant for zone 5 because we get some fierce below zero for days on end with wind. We are in the dolomite valleys of the Appalachian mtns in Virginia. So to fertilize or not to fertilize…last years soil samples of the apple orchard area, hay field and pastures came out slightly low in phosphorus (I did not sample the Gan Eden but its all cut from the same cloth. This year I spread Ida-Gro rock phosphate 500 lbs per acre, Humic DG 50 lbs per acre, Azomite 80 lbs per acre and sprayed EM-1 Microbial Inoculant including the Gan Eden. BioChar, peat moss and other amendments are used to amend soil etc. But I have in some areas very hard to work soil especially under the birch trees (any advice here?) would it hurt to add a few inches of good peaty rich soil? Avail. locally: Milorganite organic nitrogen fert for lawns 4% iron, 5-2-0, it states slow release, but 5 seems like such a low number compared to a company who makes fertilizer per species of tree and an example of their fert for birch was 8-15-30 and spruce 17-17-14, and a grouping of acid loving 15-30-8 to be entered 4″-8″ below surface. Some pretty high numbers.
Most trees and shrubs in a landscape do not need to be fertilized. Mulch your beds with organic matter and that will provide enough fertilizer.
Microbial inoculants will do nothing for your soil. You already have microbes growing there. You should not amend soil when planting trees or shrubs – they need to get their roots growing in your native soil, not in a small hole of better soil. Amending soil for perennials is less of a problem, but it is not needed. I would not add new soil under the birch. Just mulch.
I grow in zone 5, on clay soil. I have a few thousand different plants including lots of trees and shrubs. I never fertilize. But I do mulch everything with wood chips and I leave dead plant material in the garden.
More on my cut and drop method: https://www.gardenmyths.com/composting-the-cut-and-drop-method/
Thank you for your timely reply and sage advice. You have a very nice landscape project! Two subjects worth broaching. I used preen and hand pulling to keep the weeds down over the years until I could begin the under-planting, but I believe the Preen had a very negative effect on the soil (as well as very hot sun after hay mowing) I thought the soil could use a little microbe help…you still think its a waste of money? Secondly mulch gets a fungus (per university study) that water cannot penetrate. I have experimented in areas by watering heavy only to find when I pull back the mulch its bone dry underneath (1/4″ or 2″ how much mulch didn’t matter) it repelled water. This fungus issue has repeated itself every time we buy aged mulch (by the dump truck load from a landscape co.). Thirdly the (hard dry) area around the birch tree for example is slightly sloped and the wind blows everything off. I’m fighting mother nature. This was neglected farmland (not a tree or shrub on it) when we purchased it. Not a small backyard project, its quite a bit of area. The first year it took 7 dump truck loads of mulch. Two years ago we used green hardwood chips from a neighbors tree job to use on the pathways and have not seen the fungus problem quite as bad and the excess was piled up and it has composted very nicely! We have mostly red clay soil and the mulching of the pathways has really made a difference in the soil. I believe I can transfer some of the aged hardwood to a few areas. Once I get some plants going it should act to help hold the leaves etc. This spring I mixed in a few shrubs which will also help slow the wind. “The mound” sports 5 Service Berry trees which seem to prematurely drop their leaves before frost not sure if this is lack of nutrients or just their nature. You are right, I need a mulch pile…but it would have to be quite a large affair. I would be well pleased with one using biodynamics…I do have cattle and sheep on organic pastures and a few chickens but my husband throws their presents into his farm mulch pile…he is hard to train LOL! In his pile is hay by the tractor bucket load, afraid his practices will put viable seed I do not want back in the mix (his mulch pile is just a pile and not worked properly). I need my own mulch pile. Sometimes there is just no easy answer…if I could keep the leaves on some of those areas the wind sweeps clean and keep it moist to aid the microbes I might get somewhere…I have thought of using strips of bird netting during winter to hold it down. Are you chuckling by now?!
If microbes do not grow there naturally – adding them will not make them grow either.
The fungus and mold in mulch is a good thing – it helps develop good soil and is the natural way wood chips decompose. It is true they keep a light rain from getting to the soil. But once water is in the soil they keep it from evaporating.
I am located close to the coast in Texas. We either have too much rain or too little.We have a local expert that recommends deep root watering to 18″ and fertilize only with an organic. I made a tool for this and to my surprise, it cut through the clay real easy. I will fill the holes with pea gravel as suggested and I will see what happens.
Thanks for your information.
Your advice goes completely contrary to my experience with deep root feeding!
We had some beautiful short needle pines (about 60 ft. high) that started to show signs of failure–not signs–they were very close to dead!
Several so-called experts came to evaluate the situation. To a person, they all recommended cutting them down. “You’ll never be able to save them,” each predicted. And, at first, I believed them.
A day or two before the scheduled removal, I had a hunch that I should try to save them with deep root feeding. I cancelled the “morticians” and ordered a Ross Deep Root Feeder along with acid-loving-plants pellets. That was about three months ago.
Today, they are so full of needles and new growth that they look as though there was never a problem. Even the visiting “tree experts” are astonished.
I was so impressed with the results that I now give ALL my trees and large bushes deep root feeding…and it shows!
To summarize your story. You had some trees that were not doing well. You fertilized them and they did better.
I see nothing in your story that indicates the same would not have happened if you surface fertilized.