Volume 28 Issue 2, Spring 2023
by Jennifer Lumley, Audubon at Home Ambassador
Have you ever purchased a plant and excitedly put it in the ground, only to watch it weaken or, worse yet, die? Did you find yourself wondering why that happened? To reduce such mysteries this growing season, let’s consider two less familiar variables involved in plant health, and some nifty tools for better understanding habitat.
An Eastern Tiger Swallowtail butterfly visits a generous patch of Wild Bergamot. Photo by Tess McAllister
One frequently overlooked plant variable is affinity for acidic or alkaline soils. Acid-loving azaleas are a clear example of this, but other plants’ needs are less clear. For some plants, pH level may represent a condition in which the plant is better able to compete, and therefore thrive. The Wild Bergamot (Monarda fistulosa) I see in beautiful drifts on my Sunday walks does not die in my garden, but it competes poorly there so it always looks like it is petering out.
To avoid such results, it can be helpful to check the details of the habitat in which a plant naturally occurs. There’s an app for that! If you go to VAplantAtlas.org and look up Wild Bergamot, then scroll down to the habitat description, you will see that it grows best in “moderate to strongly base-rich soils.” A plant with that habitat description is unlikely to thrive in my yard’s acidic soil.
But how, I hear you wondering, do I know if my yard has alkaline, neutral, or acidic soil? Soil tests are available through the county’s Virginia Cooperative Extension office that will pinpoint the pH level of a specific planting site. For a broader understanding of your property, you can locate the ecoregion in which it lies. Bplant.org has an ecoregion locator tool that allows you to type in your zip code, then click on your location on a map. When I do this, the tool tells me that my property is located within the Piedmont Uplands Ecoregion, and clicking on that title takes me to a detailed description.
A region’s description won’t say if its soil is acidic or alkaline. It may, however, tell you about the rock below the soil. And the rock from which a soil is weathered influences its pH level. For example, soil weathered from limestone and dolomite is likely to be more alkaline, while soil weathered from granitic rocks is likely to be more acidic. Such exploration will begin to connect the knowledge you have of your immediate growing conditions with local geology.
Drainage is a second variable worth considering more closely. Also related to geology, it is distinct from simple watering needs, and compounds the particulars of soil texture (clay, loam, sand) through things like land relief, depth of below-ground water and water barriers, and the direction a slope may be facing.
The mapping tool at logis.Loudoun.gov allows you to locate any Loudoun property on an interactive map with information about many factors that influence drainage, including soil types, hydric soil, floodplains, and perched water tables. (You may also enjoy seeing aerial photographs of your property that are included and which often go back many years.) I have put together this short YouTube video to get you started.
The more you know about the habitat conditions of your property and the conditions where specific plants naturally occur, the better prepared you will be to choose plants that will be happy and healthy where you place them, and the less likely you will be to wonder later what went wrong.
If you would like help with choosing and siting native plants, the Audubon at Home program that is administered locally by the Loudoun Wildlife Conservancy is standing by. Virginia Master Naturalists and Loudoun County Master Gardeners are available to come walk your property with you, evaluate the current state of wildlife habitat, identify native and invasive species, and make detailed recommendations in a printed report. This is a free service and applications can be requested here: info@loudounwildlife.org.