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Caring for Trees

Part 4. Tree Fertilizer Products. What to Use.

By Keith BrownPublished Updated

There are a variety of tree fertilizers out there. Knowing which ones to use can be very confusing. And, to make matters worse, many quality tree friendly products are really “fertilizers” at all. Here is a list of the products I think are the best:

  1. Fertilizers – Urea has been regarded as the best nitrogen source for trees lately.

  2. Mycorrhizae (my-core-rize-uh) – These are fungi that grow on the existing root system of trees and then make their own root like system. The fungi then share the water and nutrients they absorb with the tree in exchange for sugars. These fungal spores are readily available to be applied to the soil. This is a great way to improve the water absorbing ability of a tree, and can be very beneficial during our hot, dry summers.

  3. Humates – Humic acid is a by-product of composting organic matter and is known to provide many, many benefits. The two most important benefits (in my opinion) are soil structure improvements and hormone balancing. We know that humic acids help break up tightly compacted soils which improves water and air penetration into the soil. Much of the hormone balancing effects are not fully understood, but I can confirm that regular use results in noticeably healthier trees.

  4. Growth hormones – I’m going to keep this simple to avoid a science class article. Application of a balanced mix of growth hormones has a fantastic effect on helping foliage develop to its maximum potential and stimulating root growth. If you can find a product that has a balanced mix then go for it. But, if you don’t know what you are doing, then skip this one.

  5. Micro-nutrient, vitamins and enzymes – All the good stuff we need just a little of. This is like taking your vitamins. Use of these products helps both tree growth and development and improves soil health, in turn, helping the tree. A tree fertilizer / treatment program without these products is surely incomplete.

  6. Soil restructuring – This is a process, not a product. But, soil restructuring is one of the most powerful tools we have to help trees in extreme urban environments. The idea is to take sterile, urbanized soils and reincorporate rich organic matter back into the soil. Fundamental in garden theory, but very difficult to accomplish on the scale of a large tree.

The tree fertilizer series

  1. Tree Fertilizer Part 1. An Introduction.
  2. Tree Fertilizer, Part 2: When to Fertilize Trees
  3. Part 3. How to Apply Treatments to Trees
  4. Part 4. Tree Fertilizer Products. What to Use. — this post

Common questions

What do mycorrhizae do for a tree?

Mycorrhizae are fungi that grow on a tree's existing root system and then make their own root-like system. The fungi share the water and nutrients they absorb with the tree in exchange for sugars. The spores are readily available to be applied to the soil, and it is a great way to improve the water absorbing ability of a tree — which matters during our hot, dry summers.

What do humates do for soil?

The two most important benefits are soil structure improvements and hormone balancing. Humates help break up tightly compacted soils, which improves water and air penetration into the soil. Much of the hormone balancing effect is not fully understood.

Should I apply growth hormones to my own trees?

Application of a balanced mix of growth hormones has a fantastic effect on helping foliage develop to its maximum potential and on stimulating root growth. If you can find a product that has a balanced mix then go for it. But if you don't know what you are doing, skip this one.

Are micro-nutrients necessary in a tree fertilizer program?

Yes. Micro-nutrients, vitamins and enzymes are all the good stuff a tree needs just a little of — this is like taking your vitamins. They help both tree growth and development and improve soil health, which in turn helps the tree. A tree fertilizer or treatment program without them is surely incomplete.

What is soil restructuring?

It is a process, not a product: taking sterile, urbanized soils and reincorporating rich organic matter back into the soil. It is one of the most powerful tools we have to help trees in extreme urban environments. Fundamental in garden theory, but very difficult to accomplish on the scale of a large tree.

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