3 Soil Testing Options to Diagnose Unusual Plant Problems

Foliage damage is often caused by common interior pests such as spider mites, scale, or mealybugs.  Other factors that could be making leaves wither and brown include saturated soil, maybe rotting roots, or a light level change. All of those issues are fairly easy to diagnose and fix. On occasion, I’ve come across chemical burns that have turned leaves black and yellow that were caused by a pest control technician not being careful, or an accidental fertilizer overdose. If treated quickly with the correct product, the damaged foliage will usually recover.  For the foliage that is too far gone, new plants should be put in to return the interiorscape back to normal.  

But what if the foliage in one of your atriums starts to suddenly die and you can’t figure out what’s causing it?  There’s no sign of webbing, tiny white cottony bugs sucking on the leaves, or little brown or black spots like paper dot candy stuck on the stems.  The lighting hasn’t changed, the soil moisture levels are fine, and there’s no mold, rust or fungus.  The worst part is when you replace the dying plants with healthy new ones straight from the greenhouse, and the same type of plant death starts to happen.  

In this case, there might be something going on with the soil that you can’t see.  To the eye, it has rich color, perlite to keep it aerated, and it’s not saturated enough to cause root rot or fungus. At this point, the only way to figure out the problem is to test the soil. Here are a few great options for soil testing to help diagnose the problem.

Home Kits

I first tested my problem area using a kit from Home Depot.  It was $15.00 and tested for pH, potassium, nitrogen and phosphorus.  The pH was easy to test and it showed as neutral. 

The potassium, nitrogen and phosphorus soil tests were a little more complicated.  After you add in so many parts of the soil with filtered water to the plastic container, you then mix in the coordinating capsule. Shake it a few times, and then you match up the resulting color with their color chart.  

The manufacturer recommends looking at the test in the sunlight as it can be tricky to discern the color shade of the water.  From what I could tell, the soil was depleted of all three nutrients. 

The Department of Agriculture

This government agency is available to provide the horticulture industry help with issues like these. They can give you advice through email, over the phone or if you have time to wait, an agent can come to your facility. Going to your local office and talking to someone in person is the best solution when you have a serious problem.  

However, if you bring a plastic freezer size bag of the soil, they can send it off to their lab for analysis.  For my county, the cost is $50 per soil testing sample. Besides the soil, you can also bring the damaged foliage itself with a section of the root ball. For the same cost, that can be analyzed for more answers. One tip is to make sure your foliage sample stays in a controlled environment, otherwise exposure to cold or other environmental factors can mislead the results. Check with your local county for specific details on this resource.

Landscape Suppliers

Another soil testing option is your local landscape supply company.  I have an account with SiteOne which sent my soil sample out free of charge and had my results within ten days. Generally, soil testing is a $20 charge after the first complimentary one.  The pH results matched my home test of being 6.5 or almost neutral. 

The results also noted extremely high amounts of magnesium and calcium which is basically salt. The foliage damage all started after the building began applying a COVID-19  disinfectant spray over the weekends.  The human-safe spray consisted of a high salt compound that burst open any living cell it landed on. Besides saturating the atrium soil with salt, the spray depleted the soil of potassium, an important nutrient for plant growth.  

With this new information, SiteOne was able to provide me with gypsum fertilizer that will return potassium to the soil and hopefully bring the foliage back to its healthy former glory.

If you’re experiencing foliage damage with no obvious solution, consider getting your soil tested. At the very least, it may help you find some potential solutions to bring your plants back to health.  

Sherry has been part of the interiorscape industry for over fifteen years, starting at an entry level job at North Florida's largest greenhouse and currently owning two horticulture companies. At UMaine, Sherry majored in English where she worked part-time writing scripts for a local college TV studio.

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