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Organic Answers Column - February 7, 2024 - Soil Sensor

Soil Moisture, Probes and More


Hi Howard, I appreciate being able to listen to your show on 660AM here in north Texas. I'm trying to find a good hand held ground moisture sensor for my 1.2 acre yard with a 20 zone sprinkler system. The ground has a moderate slope from south to north and has 37 mature trees. With city water being as expensive as it is I thought I'd be wise to invest in a hand held ground moisture sensor to help with my sprinkler settings for each zone. Thanks for your help.
I'm also trying to find a good weed killer for my lawn that was predominately St. Augustine and because of the extreme heat over the past couple of summers, I shut the sprinkler system off to save money and am trying to find a grass type that I can plant that will tolerate heat and perhaps a drier condition. Thanks - Dave


The only soil moisture sensor I recommend is a probe. Professional probes are available from tool companies but an old club with the head cut off works just as well to feel the moisture level of the soil.


Watering gardens and yard landscaping is a common topic for calls to the radio show, and there is no one right answer, except that setting an automatic sprinkler and forgetting it isn't the way to go. Many people wonder how to accurately determine the moisture in the soil and are looking for advice on how often to water. There is a great tool just for that purpose, called a soil probe.


A golf club can be used as a soil probe.


Commercially referred to as a pipe probe, this tool is made by several companies. Structron makes one that is about four feet long and has a fiberglass rod with a metal bullet tip and rubber handles. There are no dials or gauges; this probe works by feel. When pushing it into the soil you can tell instantly whether the soil is too dry or too wet. Then the irrigation can be adjusted as needed. It also can be used to find pipes or underground obstructions such as rock and concrete. Girdling roots on trees can also be detected without digging. This is a great tool that all serious gardeners should own and use. These tools usually run in the $15 – 20 range.


A pipe probe measures soil moisture.and (right) the bullet point on pipe probe that measures soil moisture.


The probe works by feel. If the soil is too dry, the probe won't go in the ground easily. If the soil is too wet, the probe will sound like a cow pulling her foot out of the mud as it comes out of the ground. If just right, the probe moves easily through the soil. If the probe hits something hard, it could be rock, buried construction material, tree root or hardpan caused by poor management in the past. Digging is required to figure which of these is the culprit to be fixed or removed. Hardpan is a compact layer of soil that must be physically penetrated and broken up so that drainage works and tree roots can survive.


For an even more affordable version of the moisture probe, remove the head from an old or unwanted golf club. Making a clean sharp end by cutting with a hacksaw is best. What you should not do is make or use a probe that is all metal. Using an all metal probe made of re-bar or other metal without a rubber handle is very dangerous. Electrical lines may be waiting for you!


   Be sure your golf club probe has a rubber grip for safety


The answer to the weeds and the best turf grass question is a simple one: 20% vinegar is the weed control I recommend and buffalo grass is the by far the most drought tolerant grass.






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