Trees and Soil Types

The pH balance of your soil, or the level of acidity, makes a big difference in the availability of nutrients that plants can absorb to build their stems and leaves. Different species of trees need specific kinds of soil, which affects their health and ability to grow to maturity. Learning more about the profile of your soil will determine what kinds of trees will thrive in your yard for your enjoyment and as a contribution to the area’s canopy cover.

Why pH Level Is Significant

PH stands for “potential of Hydrogen,” referring to the amount of hydrogen ions present: more ions mean a more acidic soil. The acidity of soil affects whether or not certain elements and minerals are available to a plant and how much bioactivity is present in the soil. A neutral pH level is 7; a lower number is more acidic and a higher number is more alkaline. 

A paper on Tennessee’s soil pH by the University of Tennessee Extension explains, “Plants need a proper balance of macro and micronutrients in the soil, and the soil pH has an important influence on the availability of nutrients and on the growth of different kinds of plants. For example, when the soil pH is low, nitrogen, phosphorus, and potassium are tied up in the soil and not available to plants. Calcium and magnesium, which are essential plant nutrients, may be absent or deficient in low pH soils.”

What to Know About Trees and Middle Tennessee Soil

Soil Types in Middle Tennessee

Soil pH in our area generally ranges from slightly acidic to slightly alkaline, though levels can vary quite a bit from specific location to location. In general, the Highland Rim and the hilly parts of Davidson County, such as Forest Hills, have slightly more acidic soil than the rest of the Nashville area. Within the Nashville Basin — the geological bowl in which the city sits — soil pH levels rise slightly toward the south and east, so that Murfreesboro and Mt. Juliet generally have somewhat more alkaline soils.

Michael Davie, certified arborist and NTCC board member, says the variance in soil pH levels in our region makes enough of a difference to affect your tree selection.

“Willow Oaks, which prefer a more acidic soil, can do very well here — they can grow fast and get really big, or they can do terrible,” Davie says. He cites a community in Brentwood where Willow Oaks were planted as street trees. They’ve done really well on one side of the street, but not as well on the other side.

Many other trees which prefer more acidic soil generally do not do well over the long term in Nashville. At the top of this list is the White Pine, which rarely flourishes here. Davie also mentions Leland Cypress, Serviceberry, American Hornbeam and River Birch as trees that can fare poorly in Middle Tennessee. The River Birch, for example, can grow pretty fast here for about 20 years, then weaken and die.

Your Yard’s Soil

So what’s the best way to learn the specifics of the soil in your yard? A simple, inexpensive soil test. Most soil tests measure the available main nutrients (including nitrogen, phosphorus, and potassium), soil pH (acidity or alkalinity), and organic matter content. Healthy topsoil is rich in bioactivity and organic matter, as well as a texture that is well-aerated to hold oxygen and water.

While DIY soil tests are available, you can also get a test done by the University of Tennessee's Soil, Plant and Pest Center at the Ellington Agricultural Center in Nashville. For $15, roughly the same price as a DIY kit, you can mail a soil sample to the university and receive an analysis back in under a week. These location-specific results also come with instructions on how to manage your soil for deficiency or saturation. Learn more on how to submit a soil sample to UT here.

Trees and Your Soil

Early fall is a great time to get your soil tested. This way, you’ll know before fall and winter planting which trees are likely to do well in your yard. 

Some trees that prefer slightly acidic soils are Red Maples, Sweetgum and Tulip Poplars. Others will grow well in alkaline soils, such as Sugar Maples, Bur Oaks and Sycamores. These and other Nashville-friendly trees are available through the Nashville Tree Conservation Corps’ tree sale, which is celebrating its 5th year.

To help a tree grow from sapling to towering specimen, it will require attention throughout the year. Make sure the tree gets enough water and isn’t subjected to damage from weed trimmers or mulch domes. Checking your soil pH at least once every couple of years will help maintain it in generative condition for the health of your trees, grass and plants. 

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