Garden SPC - Monitoring (and Improving) to Ensure a Good Harvest!

Jim Oskins | 8/14/2023

Topics: Predictive Analytics, Minitab Connect, Real Time SPC

Learn how Minitab’s Statistical Process Control (SPC) solutions helped my wife and I improve our garden this season, demonstrating that SPC can really help bad news travel faster. We could correct issues ASAP (despite our busy schedules) before the tomatoes died. This reminded me so much of our roles in the industries we have both worked in - automotive and home appliance engineering.

Specifications for this project:

  • Most crops need a pH between 6 and 7
  • Peppers are an exception; they prefer more acidic soil 4.8 to 6 pH
  • Corn can go up to a slightly alkaline pH of 8 and be just fine
  • All plants seem to like 40% to 80% moisture content… which in my meter’s language are from “normal” to “wet+” … “dry” or “dry+” would be bad


The Shortcomings of Using Classical SPC Techniques

Bad news travels slow if you only use classical control charting. For many it’s enough of a hassle in their busy day that sometimes they will delay, procrastinate, or nottonks even make the control chart! Real life gets in the way. Even in the best circumstances, you must manually collect data, take it back to your desk, analyze it, and act on that. All those things take time and waste money.

  • In my case, a bad pH or dryness reduces yield or kills plants.
In our old industry cases scrap would build up, costing a fortune… or worse (quarantine products or in some cases release bad products to customers!)

control charts

Eliminate Manual Steps: Getting an Automated Dashboard View

Minitab Connect is a very powerful tool. It lets you connect to databases (or in my garden SPC - create forms for data entry) and stats and graphs from those data can be automatically displayed on a live dashboard.

I take my phone out to the garden with my pH and moisture meter (pictured below) and collect data throughout the different zones in our garden. This automatically charts on a dashboard visible to my wife (even though she doesn’t have a subscription to Minitab Connect like I do, she can still see the dashboard!)

If it’s out of control high, one of us will add some plant clippings to lower the pH. If it’s on the low side we’ll add some wood ash from the fire pit to increase the pH.

Minitab connect dashbord


Diving Deeper into the Data

At one point the data led us to a question: “does the moisture level change the pH?” It sure seemed like any time we had a reading of “normal” moisture the pH was near 7. When the moisture was “wet” or rarely “wet+” the pH seemed to be lower. A lot of things seem to influence pH, like the soil depth at which the probe was placed. I could have done a DOE on all these factors to get more information.

I was able to use the data already collected by Minitab Connect though! Just like in industry, where your end of line test equipment is collecting tons of seemingly unrelated data… sometimes you’ll find insights that can help lead you to cause and effect relationships if you analyze it all together. Minitab’s Predictive Analytics (machine learning) is a favorite of mine to do this type of modeling of observational data.

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I could not resist (even though my garden data set is much smaller than my old automotive or home appliance data sets). I exported from Minitab Connect to open with Minitab Statistical Software. Automated machine learning quickly told me to stop worrying so much about the plant line (corn, tomato, beans, etc.) and focus on this very clear relationship between moisture and pH! I liked the output so much I added an additional page to my Connect dashboard with a simple graphic revealing this relationship:




acidic water (3) From left to right we have the pH from all six zones of my garden at “normal” moisture, then “wet” and then “wet+.” The pH decreases with moisture level. This may  not be the case for you but (somewhat to my surprise) our well water is acidic with a pH ~ 4! That’s tough for plants that would prefer to be around 6 pH.

So now if a zone gets too damp then my wife or I will turn off those spray nozzles. Each zone, luckily, has its own set of spray nozzles… a Christmas gift from my mother, believe it or not. This turned out to be very useful towards increasing our garden yield this year.

What MakES Minitab Connect different than other BI tools?

Minitab Connect (and/or a related product: Minitab Real-Time SPC… ask us if you’d like to know the subtle differences) does a lot of the things other Business Intelligence (BI) tools can do but also so much more. As you’ve seen in this gardening story, automated statistical analysis can tell you where and how to work on problems. Deep dives to test theories or reveal new insights is also super easy with all the power of Minitab at your fingertips!



Please reach out to us if you would like to learn more about these solutions.