Soil science is very interesting. The complexities of ions, pH levels, nutrient uptake, and soil horizon are indeed as diverse as they are complex. The health and micro-diversity of the soil greatly contribute to the health of trees.

Soil maintenance is often overlooked when it comes to tree health and maintenance. The problems we see above ground are often linked to the important organisms, nutrients, and water cycles below the surface.

Soil science is a profession of its own, but I would like to take a moment to identify a few helpful tools and practices homeowners can make to improve the soil and assist in tree health and vigor.

What’s pH all about?

pH means potential Hydrogen. It specifies how acidic or basic (alkalinity) a given solution is. Soils that measure low in pH are acidic (0-7), and those that measure high in pH have greater alkalinity (7-14). Most soils fall between 4.5-10. A pH of 7 is neutral.

Once mixed with water, a soil pH test will measure the hydrogen+ ion concentration within the soil sample. Once we know if the soil is more acidic or basic, we can better understand what nutrients are available for uptake.

Nitrogen (N), Phosphorus (P), and Potassium (K) are some of the main macronutrients that many trees and plants need to survive.

However, many micronutrients are just as important to maintain the health and vigor of a tree. Even though your soil may have high levels of macronutrients available, if the pH is reading high levels of acidity or alkalinity, these nutrients may not be available for uptake. Alternatively, the tree may uptake too much of this nutrient and have an adverse effect. Once you determine the soil’s pH, consider conducting a soil nutrient test on macronutrients such as N, P, K.

STEP ONE: Conduct a pH soil test.

STEP TWO: Conduct a Soil Nutrient test.

Companion Planting

Companion planting has many benefits for our landscapes. Companion planting is used to support benefits between plants, such as fixing nitrogen, encouraging pollinators, promoting biological controls, and maintaining diversity in our gardens and yards.

There are many resources available on this topic. We encourage you to consider companion planting in your garden and landscape objectives. Find companion plants that support healthy micro-ecosystems.

Each site is different, so ensure the plant is suitable for the desired location. An example of a good companion plant is Comfrey Symphytum officinale. This medicinal herb has vigorous growth, favors well-draining but moist soils and full-to-part sun, and is well suited for bringing nutrients deep in the soil closer to the surface.

Incorporating native trees and plants that are suited for the site can assist in building better soil texture and structure. Roots provide aeration and water to be trapped within the soil particles. Allowing plants and trees to take up nutrients.

As we build diversity in our landscapes, we promote many biological controls against unwanted pests. This is called mono-cropping, when we have a landscape full of one species.

The plants can be extremely vulnerable to attack in the event of a disease or pest. With diverse plants combating pests and pathogens, your landscapes and gardens are better equipped to face these attacks while maintaining health and vigor in the soil and in their companion plants.

Composting and Organic material

As tree workers, we obviously find ourselves in people’s yards all across the city. We have noticed that clients with landscapers who “clean” their yards weekly by removing every last leaf, needle, or twig often ask us, “Why does my tree look so sick”?

Trees and plants need organic material to thrive. When trees drop their leaves in the fall, they fertilize the soil within the drip line. The richest soil horizon for growth is the “organic” horizon.

So it’s no surprise that the best promoter of plant growth is the amount of organic material within the soil. The soil around Portland, Or, is high in clay. Soils high in clay are difficult for root growth and proper water drainage.

Organic material helps build a more suitable structure for available nutrients, water, and air. We encourage and promote either building a compost bin or wheel to collect organic debris from your yard and allow the compost to fertilize your trees and plants throughout the year.

STEP THREE: Collect and spread compost to plants and trees.

The strength of soil is dependent on so many factors—some outside of our control—such as long periods of drought. Plants play an essential role in maintaining soil health. These few items listed above can have large impacts on building a healthy soil profile.

In short, knowing the condition of your current soil structure and continually adding organic matter will improve and maintain your soil. So next time you start to see some wilting or discoloration on your tree, remember to look down and start digging.

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