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Wikipedia has a great article on soil moisture sensors, but it focuses on commercial/farming/large-scale settings. I'm investigating options for consumers, and I'd like to understand what technologies are available for my front yard. (I would also ask for product links, but I believe those are discouraged on StackExchange sites ...) So my questions:

  1. What moisture sensor technologies are commonly and successfully applied by consumers?

  2. Investigating one such product, I came across the following gem explaining their technology:

Baseline Soil Moisture Sensors work by sending a high frequency pulse of electricity down an embedded wire path. The high frequency of the pulse causes the sphere of influence to move outside the sensor blade and into the soil around it. When the pulse travels through moisture, it slows down. The sensor measures the speed, and then converts this measurment to a moisture content reading.

Assuming they don't mean "the sphere of influence is moved by advanced magic muggles can't possibly comprehend", what technology might they refer to and how does that work?

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  • Poorly? The things are conductivity based, and that depends on not only how much water is in the soil, but which ions N,P,K,Ca,Mg etc. are in the water. The meters will give you consistent answers for one soil type, and one level of fertilization, but should you change either of those you'll get different results - at the same moisture content. If you want real moisture numbers, take a 10g soil sample and bake it in a 200°C oven for 2 hours, then weigh again. – Wayfaring Stranger Sep 5 '15 at 15:17
  • From what I can tell, there are some other schemes that don't rely on conductivty, but do they exist / are they practical for consumers? – Johannes Ernst Sep 7 '15 at 4:44
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Based on what I can see from install requirements and explanations it's working on electrical conductivity. The sensors periodically send out a small pulse of electricity from one side of the device. Then the device measures how long it takes for the pulse to travel from one side to the other. Depending on how moist the soil is the pulse will travel slower or faster. Then it calculates how much soil moisture there is based on how fast the pulse moved. In models like the one you showed, it also has the ability to trigger a sprinkler/irrigation system if it detects that soil moisture has fallen below a set level.

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Moisture sensors are worthless. They do not tell you anything that you couldn't discover on your own just by knowing your plant needs and your soil conditions. Never have I used one...oh I played with one or two but forget it.

The important thing to know and remember is to WATER DEEPLY and ALLOW TO DRY OUT before watering again. A little every day or every other day is WRONG. After watering your plants or lawn go out and using a spade dig down to see how far the moisture went. Soil should be moist 4" in depth after a watering. There are questions/answers on this site that explain how to TRAIN your plants to develop deep roots to make them drought tolerant. You need to allow the soil to dry (from the top down so roots have to grow longer to get at the deeper moisture). No technology can replace a gardener who has been involved and alert to their plants environment, NONE! Throw those sensors out! They do not mean anything to gardening...trust me. Water deeply and allow to dry out!! Watch your plants, if they are shallow rooted they will begin to WILT. Water deeply and allow to dry before watering again. This actually saves LOTS OF WATER. Need to know what type of soil you have, are your plant beds fluffed up so as to absorb water and drain well? Are you using automatic watering? If so, you can also do a test with kitty kat cans (any can that has straight sides) by placing them all over the site the zone covers. You want 1" of water per week minimum. If you have clayey soil (I MISS clay soils!!) I'd try at least 30 minutes per zone (not the 10 or 15 minute gig!), dig down to see how deep the moisture at 30 minutes gets...4" minimum. Otherwise you are training your grass and plants to be shallow rooted and the day they don't get watered they get stressed and plants/grasses only get 2 or 3 stressed out 'cards' before they go to plant heaven.

Even though I am a bit biased I will go look at this site you posted. Do you have a maintenance company or do you actually get involved with your yard? Which would you prefer? I'll be back of course but my answer is to NOT use moisture sensors. Get aware and used to the different needs of your plants and lawn.

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    It would be nice if you answered the questions (assuming you know the answers) and left out the editorializing on subjects that have nothing to do with the question as asked. – Johannes Ernst Sep 4 '15 at 22:31
  • Sigh, sure. I didn't say what you wanted to hear...sorry. Grins...just trying to HELP others who don't GET IT. Moisture sensors are worthless. That is my opinion and I have earned the right to say so...contact the companies that produce these...sensors! I am sure they'll say what you want to hear. Gee I am so very sorry to have spent so many brain cells trying to HELP you. Grins...amazing. – stormy Sep 4 '15 at 22:44

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