Soil Test Results Say Back Off Organic Matter! What?

My soil test results contradict everything a gardener is told to do. As promised, I received a letter in the mail less than two weeks after submitting the soil samples to the lab detailing the shortcomings. As it turns out, both areas are pretty similar despite the fact that one is an established garden, the other hardly touched except for the tricolor beech and two Techny arborvitae that are no bigger than a minute. But there’s one significant difference and it’s a game changer.

The redbud garden, which is no longer home to a redbud on account of verticillium wilt, was one of the first gardens I dug almost 20 years ago. It’s seen a lot of compost which explains why it tested “very high” for organic matter. A whopping 10.0! Too much organic matter can be a bad thing. Ummm, wait, what? Unfortunately, there’s no hard and fast recipe for making good soil. Everyone says add compost, add manure. But no one ever says STOP! The only way to know what you have is to test the soil first before you add anything. What I discovered is that too much of a good thing can be a bad thing. Kinda like chocolate or gin and tonic.

Plants have struggled in the redbud bed for years and now I understand why. Soil matrix is fascinating. With so much organic matter, I expected to see a very high level of phosphorus as well. The two are closely connected. As organic matter decomposes, it uses up all the oxygen in the soil while also contributing an explosion of mineralized nutrients that are unavailable to plants due to an excess of phosphorus which inhibits a plant’s ability to take up nutrients. The high pH isn’t helping either. When greater than 7.0, phosphorus and other trace minerals are less available to plants. The pH of the redbud garden is 7.5, the tricolor beech garden 7.4, so basically the same alkalinity. All that goodness just sits there, slightly out of reach. It’s like dangling food before a starving caged animal.

At 5.7 for organic matter, the soil in the tricolor beech garden is considered high with an equally high phosphorus level. So here’s my plan. I’ll add two inches of compost to the new garden to improve tilth and help with drainage. The lab recommended ammonium sulfate for the redbud garden. It’s N-P-K or Nitrogen-Phosphorus-Potash analysis is 21-0-0, so no phosphorus in this amendment. It’s commonly recommended for alkaline soils to lower pH and considered an inorganic fertilizer despite having come from naturally occuring mineral deposits. It’s inorganic because it goes through a manufacturing process.

Out of curiousity, I reached out to the Espoma company to get their take on an organic equivelant. Here’s what they suggested based on my soil test results which are totally unique to my garden.

• Plant-tone (5-3-3): 8lbs. per 100 sq. ft. divided into three applications; early spring, late spring and later in the fall.
• Holly-tone (4-3-4): 10lbs. per 100 sq. ft. divided into three applications to add sulphur and help lower pH.
• Blood Meal (12-0-0): 3.5-4lbs per 100 sq. ft. divided into three applications for a constant long lasting supply of nitrogen.
• Palm-tone (4-1-5): 10lbs. per 100 sq. ft. divided into three applications.
• Soil Acidifier to help lower pH.

This isn’t a one-size-fits all, although I kinda wish it was. It would make fixing the soil so much easier. So don’t apply my recommendations to your garden. Your needs could be totally different from mine. With the exception of the Palm-tone, I already had the recommended amendments. The Palm-tone was a surprise given that I live in the Midwest and there’s not a palm tree in sight.

So that’s it. Soil science is mind blowing and quite honestly, a little overwhelming. There’s so much more to know and I’ve only just scratched the surface. I think that’s enough for me. All I wanted was a window and I got a cargo door. But I think the most important thing a gardener can do is get a soil test and adjust based on what your soil reveals. Pick plants best suited to your unique growing conditions. In other words, don’t fight it. I wouldn’t dare grow acid-loving blueberries in the ground.

Life’s too short for such fruitless endeavors.

Curious about what’s happening in my garden? Check out the latest video on my Here She Grows YouTube channel!