Thread: The Low-Down on Tree Fertilization

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  1. #1
    Oak
    Join Date
    Jun 2008
    Location
    Western NY, Zone 6
    Posts
    348

    The Low-Down on Tree Fertilization

    My arborist stopped over today, and one of the items we discussed in detail was fertilizing trees, young and old. I jotted down (on paper) what he outlined for me, so I'll post the info here which will hopefully be helpful to anyone and everyone considering a fertilization schedule for their trees...

    * First and foremost, before putting any fertilizer down, have your soil tested professionally, this is usually a service provided by your County Soil and water conservation district. Cost is MINIMAL, only a few $. This will give you a good idea of nutrients that are lacking in your soil, in addition to your soil pH.

    * Trees planted while they are DORMANT (meaning no leaves or bud activity) can be fertilized lightly in the early Spring (late February or early March for you Southern folks) with a balanced liquid or granular fertilizer. This does NOT have to be done every year, a 3-4 year schedule is usually fine. Spring is also a great time to fertilize established trees, especially ones that show reduced vigor and growth from a previous season.

    * Trees planted during the growing season (whether bare root or containerized) that have broken dormancy should NOT be fertilized until ALL leaves have dropped in the Fall (for any deciduous trees). Newly-planted evergreens can be safely fertilized in the late Fall once a few frosts/freezes have occurred. Reasoning behind this suggestion: if you fertilize a tree in the late Summer or Early Fall before it has dropped all its leaves, the tree may push new growth which will probably not HARDEN off before the Winter sets in. This can cause die-back and can stunt the tree's growth.

    * KNOW when to fertilize certain trees. Dogwoods, for example, typically grow within canopies of forests where the soil is rich in compost and nutrients. Dogwood leaves may yellow after awhile if there is a nutrient deficiency in the soil. Other trees that thrive naturally in dense forests will fall into this same situation. Fertilize (and water-in) when leaves become discolored or yellow. Chances are good that your yard will not compare to the nutrient-rich soil found in a forest.

    Fertilizers are labeled N-P-K, so a 25-5-10 contains 25% Nitrogen, 5% Phosphorus, and 10% Potassium (per bag, the rest is "filler"). In terms of trees, Nitrogen will cause more vigorous new growth to be pushed out, the Phosphorus settles into the soil slowly but motivates the tree roots to grow more vigorously, and Potassium (often Pot Ash in granular fertilizers) give trees thicker and more robust cellular structure, improving the overall hardiness and strength of the tree.

    The next question is often how much to use, or which type to use. First off, avoid fertilizers which have high Nitrogen content (first number above 25, for example 30-5-5). If applied in excess, the Nitrogen can burn the roots of your tree and cause die back.

    Granular fertilizers are a good choice because they release their nutrients more slowly into the soil, but more rapidly than organic fertilizers such as manure. Granular fertilizer should be spread over the mulch or the root zone of the tree in a similar manner that it would be spread on a lawn; the grade of fertilizer being used (10-10-10 or other balanced fertilizers tend to be the safest bet) and nitrogen content generally dictate how much to spread over 1000 sq. feet. If you use a broadcast seed spreader, you can set the dial on the spreader as per the recommendation of the manufacturer of the fertilizer. Otherwise, you can search Google for fertilizer spread rates based on Nitrogen Content. If you already fertilize your lawn on a schedule with a granular fertilizer, don't be afraid to broadcast it right over your tree mulch in the early Spring and late Fall. You should not fertilize during the mid or late Summer months, this is bad for both lawns and trees because it will cause stress especially if the weather is dry.

    Liquid fertilizers are another option, and provide the most rapid release of nutrients to your trees' root systems. Miracle-Gro and a number of other liquid fertilizers for general garden or specific tree use are the most suitable. Fertilizing with liquids is appropriate for those on-demand applications where the tree is in need of fertilizer, such as the case of the Dogwood example I gave above. Again, balanced fertilizers with reasonable Nitrogen content are preferred.

    Finally, organic fertilizers, such as peat moss, compost, or manure, can be used at any point, but generally only provide Nitrates (broken down to Nitrogen) at a very slow pace. There is no guarantee when using an organic fertilizer that Phosphorus and Potassium are being provided. It's a good idea to add some compost (such as peat moss) when planting a new tree. Till it right into the soil within the hole you dig for planting the tree.

    Why use a balanced fertilizer? A fertilizer that is really high in Nitrogen (such as 40-5-5) must be spread conservatively to avoid root burn, therefore providing a tree with a good amount of Nitrogen, but very limited amounts of phosphorus and potassium. With a balanced fertilizer, no matter which spread rate you use, equal amounts of nitrogen/phosphorus/potassium will be distributed to the tree. Depending on where you live, some areas do NOT allow the use of phosphorus, as it is very harmful to lakes and streams. If you live near a body of water, NEVER use a fertilizer with any phosphorus content (middle number must be 0).

  2. #2
    Sapling
    Join Date
    Aug 2008
    Location
    Southeastern Wisconsin
    Posts
    73

    RE: The Low-Down on Tree Fertilization

    Hey very useful information! Sounds like you really look forward to the days when your arborist comes over for a chat!

  3. #3

    RE: The Low-Down on Tree Fertilization

    Sounds pretty reasonable.

    Myself ?? - I'm an arborist and I rarely fertilize my own trees, except maybe once to help them boost the size the first couple of years - but I don't think it helps their form.

    My approach to tree feeding / fertilzing is here:

    http://www.mdvaden.com/tree-root-feeding.shtml

    After 30 years working with trees in this area, I feel that fertilizer "may" offer a healthier tree in strict sense. But apparently the fertilizing diminishes natural growth characteristics and often seems to produce structurally weaker trees.

    In other words, if they don't have to have fertilizer, I think the trees can hold up better to storms and inclement weather better.

    M. D. Vaden
    Oregon

  4. #4
    Oak
    Join Date
    Jun 2008
    Location
    Western NY, Zone 6
    Posts
    348

    RE: The Low-Down on Tree Fertilization

    M.D. Vaden -

    Agreed. My county arborist essentially said the same thing yesterday - fertilizer can be a good booster for a few years, but once a tree is established, it should push lots of new growth and thrive on its own with little to no help. He picked on my Dogwood the most since its leaves tend to yellow and fade a bit in typical yard planting scenarios, so it might need fertilizer even after it has established itself in a few years.

    He was impressed with the way my trees had grown in just one year, he mentioned that the light fertilization in late Fall and early Spring probably had something to do with the explosive new growth and vigor on some of the younger trees, especially the River Birch and Swamp White Oaks. He spotted out some aphids on a few of the trees but said they shouldn't be a problem. Some of the foliage on my Swamp White Oaks looks like cheese cloth because of gypsy moths, and apparently the store-bought "once-and-done" insecticides (for trees/shrubs) are particularly weak (according to the arborist) because of the push over the years for environmental friendliness (a good thing I guess). The native trees are always hit harder by insect damage because that's what the insects are accustomed to eating, but the Swamp White Oak is a hardy species and is designed to take the insect abuse. I just don't like my foliage looking like swiss cheese, so next year I will buy some Bayer Advanced and will treat the swamp white oaks in the Spring in hopes of keeping the foliage in better shape.

    Western NY is known for having good, rich, fertile soil (we produce some of the best corn and veggies in the US), so fertilizing is really a minimal routine throughout our area. Other sections of the US have much poorer soil conditions (rocky, tough clay, sand, etc.), so fertilizing trees in those areas is almost essential.

  5. #5
    Oak
    Join Date
    Jul 2007
    Location
    Northern Minnesota-zone 3
    Posts
    300

    RE: The Low-Down on Tree Fertilization

    I think if we mostly plant suitable trees for the type of soil, moisture content, etc., then fertilizer is really unnecessary.

  6. #6
    Oak
    Join Date
    Mar 2009
    Location
    Sylva NC zone 7
    Posts
    276

    RE: The Low-Down on Tree Fertilization

    That would put you with very little choices except for things that can take bad soil.

  7. #7
    Oak
    Join Date
    Mar 2007
    Location
    Central Oklahoma - Zone 7 for now
    Posts
    548

    RE: The Low-Down on Tree Fertilization

    Adding fertilizer does not stimulate new growth at all. I see a number of 'false statements' about when to add fert - no relation whatsoever to a tree's growing pattern. Ferts only make available nutrients for growth, not the chemicals that stimulate buds or whatever. Withholding nitrogen at times will help reduce internode length leading to a more 'compact' tree for those that like a tighter canopy or such, and possibly making a limb stronger by having a 'shorter' overall length (less weight further out from trunk). But adding nitrogen will not cause tree to extend 'unnaturally' as other hormones are involved in stimulating the growth to occur in the first place. I don't think that the chemicals that make growth happen are available to the average tree-planter (???).

    There are many 'fallacies' about using ferts to make trees grow. Poor myths at best. Ferts only allow *better* growth when such is going to happen. More is not better - in all aspects. Adding ferts will not alter growing patterns either as the sun/temp play a MUCH bigger role in the timing of the chemicals within the tissues, etc.

    I add ferts whenever the soil indicates it needs such, either through test(s) or by observation over the years, so to speak. I have never gotten a tree to burst buds by adding a fert - unless root-stimulating hormone is a fert, LOL.

    If a tree is removing nutrients from the soil (growth) and those nutrients are removed from the cycle by not allowing them to rot/decay over the root-zone (raking leaves/bagging clippings, etc), then it will be best to replace those nutrients through artificial means of fertilizer application(s). If tree is sitting in its own 'compost', no addition should be necessary other than minor stuff for 'special' species needing more than local ecozone provides. Some species can even fertilize themselves by atmospheric absorption (leguminous stuff)!

    Just a few thoughts...
    Alex

  8. #8
    Oak
    Join Date
    Jul 2008
    Location
    Indiana
    Posts
    198

    Re: RE: The Low-Down on Tree Fertilization

    Quote Originally Posted by alexinoklahoma
    Adding ferts will not alter growing patterns either as the sun/temp play a MUCH bigger role in the timing of the chemicals within the tissues, etc.
    Moisture relative to how much a certain species desires has to be near the top, if not the very top. The difference I see in Red Maples and Walnuts coming up in moist vs. dry locations is usually pretty dramatic.

  9. #9
    pwk16
    Guest

    RE: The Low-Down on Tree Fertilization

    Be careful, overfertilization can inhibit flowering in fruit trees and excessive green growth is a very large dinner-bell for insects. I work for Arbor Day Foundation and I have heard all kinds of horror stories about people fertilizing perfectly healthy trees that are 30-50 years old only to have the tree drop all of its leaves and take years to recover. Be careful.


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