Problems With Tree Over-fertilization

How to Avoid or Correst Over Fertilization

Using the Right Fertilizer Ratios

You need to stay with the higher ratio nitrogen fertilizers unless your tree is determined to be deficient in potassium or phosphorus (take a soil test). Using nitrogen in large quantities can come with some risk and need to be handled with care.

Using an equal ratio of nitrogen, potassium, and phosphorus when not needed can have the opposite effect, becoming a potassium and phosphorus salt dump.

 Excess fertilizer alters the soil by creating too high of a salt concentration, and this can hurt beneficial soil microorganisms.

So, fertilize trees using the proper method with an N-P-K (nitrogen, potassium, and phosphorus) ratio of 10-6-4 which is a great choice and would be even better in a "slow release" formulation in most cases. Slow release means that your fertilizer product is not a liquid but is locked up in granules that release slowly.

Stay at less than .20 pounds of nitrogen per 100 square feet of root zone application area depending on tree species and size. Any time you exceed this recommendation you will create a situation for on-site contamination or a potential for runoff pollution. Extreme contamination could harm the site for a very long time.

How You Can Over Fertilize a Tree

You can actually kill a tree if you apply too much fertilizer. Remember that applying high levels of quick release nitrogen can burn the roots when soil applied and burn the foliage when foliar applied.

When applying too much potassium and phosphorus, all will lead to intolerant salts for plants to endure.

Important: The most common ways to over-fertilize a tree is:

  • over-using an equal ratio of all three essential nutrients (nitrogen, potassium and phosphorus).
  • applying more material than the standard recommended application rate suggests.
  • using fertilizers that are designed to be "fast release

Combining any or all of these conditions will increase the chance of tree root damage. Too much fertilizer introduces toxic "salt" levels to the root system which will harm a site for future planting.

How to Treat an Over Fertilized Tree

OK. So you realize you may have over fertilized your tree. Usually, this happens when you ignore the application rates or you spill high nitrogen fertilizer mixtures near tree roots. Often you don't know until symptoms occur. 

Let's look at the symptoms displayed by an over-fertilized tree. Symptoms can appear on or near a tree as:

    • A crust of fertilizer on soil surfaced under the tree drip zone.
    • The yellowing, wilting and browning starting at tree leaf tips and margins.
    • The tree starts to drop leaves before dormancy.

    The tree may survive and the site much improved if you do a fairly simple, three-part treatment as quickly as possible:

    1. Remove the dying or wilting leaves, if you have any, to reduce fertilizer remnants.
    2. Water the fertilized portion of the soil to a "flushing" point. Obviously that means you need a local source for a lot of water.
    3. Cover the critical root zone with a carbon-based mulch. It should preferably be composted leaves and grass. You should do a second flush over the composted mulch.
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      Your Citation
      Nix, Steve. "Problems With Tree Over-fertilization." ThoughtCo, Nov. 15, 2016, Nix, Steve. (2016, November 15). Problems With Tree Over-fertilization. Retrieved from Nix, Steve. "Problems With Tree Over-fertilization." ThoughtCo. (accessed March 21, 2018).