Soil Enhancement is Better Than Fertilization

Why Fertilization Alone Is Not Enough for Trees

Fertilizing your trees can be a very important step to keeping them healthy in an urban environment. But one step that is commonly skipped is actually enhancing the soil while performing this fertilization. The difference between feeding trees and building soil fertility is more significant than most homeowners realize.

We can go down a deep rabbit hole when talking soil science, but today we are just going to scrape the surface.

The Problem With Standard Tree Fertilization

Fertilization is commonly done as a liquid fertilizer or a granular/solid fertilizer. While each has its pros and cons, our preferred method is liquid fertilizer delivered via vertical mulching — more on that in a moment. For trees, liquid fertilizer should be delivered with a wand that goes between 6 and 12 inches deep.

Many of the fertilizers used for trees and lawns add little to no organic matter to the soil. They add an abundance of NPK (nitrogen, phosphorous, and potassium) which is good for plants in the short term, but does not replenish the soil of anything taken up by the plants. Chemical NPK is quickly available for the plants — but then is flushed from the soil after only a few weeks or months.

Soil Enhancement: What Actually Works

We prefer soil conditioners with a lower percentage of NPK paired with other organic materials. When it comes to liquid fertilizer, we prefer seaweed extract, mycorrhizal fungi, humectants, and naturally sourced surfactants to help mitigate hydrophobic soil rapidly.

We also use what we call “hard fertilization” — using an air spade that blasts compressed air at high speed to expose roots and mitigate soil compaction without damaging the root system. After we blast holes or trenches, we fill them in with a mix of leaf compost, comtil, fine-meshed pine bark mulch, worm castings, and other amendments on a case-by-case basis. This method costs more upfront, but yields long-term benefits to both the soil and the trees simultaneously.

What You Can Do Yourself

There are things you can do to improve your soil without hiring an arborist. Do not rake your leaves — mulch them instead. It only takes the lawn mower a few passes to mulch them up well, and the impact on soil health over time is significant. You can also spread worm castings over your yard or root zone using a spreader. Worm castings have a high concentration of nutrients and will help replenish the soil at a fairly rapid pace.

Think Soil First, Trees Second

When considering fertilization, it is always best to think about it as building fertility in the soil rather than feeding the trees. This will greatly improve the health of all of your plants and help the soil build a diverse, healthy microorganism population that supports tree health for the long term.

If you have trees that are showing signs of decline, poor vigor, or slow growth, a soil assessment is one of the first things we evaluate during a consulting visit. Our plant health care program includes soil amendment as a core component of everything we do.

James Benedetto — Owner, ISA Certified Arborist OH-7011A, Arborist Solutions