Start With Your Soil

Money wasted. Plant trees with more care. Contributed photo.


By Kit Flynn and Lise Jenkins

Right now, it’s all about the plants. We’ve sat inside long enough reading catalogs and cleaning our tools. Our fabulous friends are arriving at nearby garden centers, and we can’t wait to bring them home.

But wait.

Take the time, first, to pay attention to your soil. Stop — I can see your eyes rolling. Before you ignore me, I’d like to share a $10,000 story.

Recently, I started helping a group with their landscape projects. One of the group members mentioned that they had spent $10,000 for deep-root fertilizer injections on 43 trees last year.

I’m not going to debate the effectiveness of this technique, but when I asked the group for their reasons, they replied that the trees were struggling and looked sick. They overlooked something basic: their soil.

The trees in question were planted in highly compacted clay soil. A contractor had dug holes in the ground and dropped the trees in while mounding up mulch around the top. Of course, they were struggling.

I’m going to skip to the end of my story and work my way back. We tested the soil and discovered it had a pH of 4.9. That’s a big part of the reason why the trees were struggling — they are sitting in acidic clay pots.

Here’s a simple soil chemistry lesson: Remember, I’m a gardener, not a chemist, so I’m glossing over a lot of details. First, pH is a logarithmic scale that measures acidity. Each of the 14 values in the scale signifies a level of acidity 10 times greater than the preceding value — so a slight move up or down has a big impact on our plants. At the low, acidic, end of the pH range (< 1), we find things like battery acid. In the middle of the scale, e.g., values around 7, we find neutral substances such as pure water. Finally, at the high end of the scale (13+) we find highly alkaline substances such as lye.

The pH of your soil underlies everything else because it controls other chemical processes that impact your plants — including a plant’s ability to take up nutrients and water. While some plants have adapted to survive in either acidic or alkaline soil, most garden plants do best in soil with a pH in the range of 5.8-6.8.

Back to our story: Because the soil around the trees was so acidic, their ability to absorb nutrients was severely restricted. As a result, the $10,000 fertilizer project was money wasted.

Our state has a wonderful soil testing service. Soil test kits are free of charge from your county’s Cooperative Extension Service office. You can find your county’s office here:

From April to November, it’s a free service — you can return your soil sample to your county Cooperative Extension Service office, they will submit it for testing, and you will get your results back in a few weeks via email. Between December and March, the soil labs are busy processing samples from North Carolina farms, so they charge homeowners $4 per sample.

Your soil sample report will show both the pH of your soil and how to treat your soil to achieve the optimum pH for your plants. It will also provide information on the composition of your soil and the amount of other nutrients you should apply. This takes the guesswork out of fertilizing your garden. There is no need to buy costly amendments your plants don’t need.

Back, again, to the $10,000 trees. We tested the soil, and the report recommended applying 60 pounds of lime per 1,000 square feet to increase the pH value. That’s a lot of lime, so the group is spreading lime this spring and plans to do so again come fall. It will take some time to bring the pH up, and we hope their trees will survive during the interim.

Twenty-eight dollars of soil testing and a few hundred dollars of lime will prove to be money well spent. Anything left in the budget can be spent on what we all want — more plants!

Absent from their gardens, Kit and Lise enjoy roaming our region exploring the intersection of horticulture and suburban living. More on Instagram @AbsenteeGardener or email:

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