All that any moisture meter is measuring is the electrical conductivity in the soil, something that moisture allows. so theroetically any meter that measures conductivity would work. However, something that is close to accurate needs to be more than just a dressed up and inexpensive Ohm/Amp/Volt meter and they are very costly.

There are microwave methods, neutron scattering methods, ceramic uptake methods, a raido[something] methods, Kimmsr's impedance method and others.

A few are discussed at In situ measurement of soil moisture: a comparison of techniques

One of the techniques we used in the university lab and perhaps mentioned in the article above is just weighing the whole container before and sporadically thereafter giving a fair guess at the moisture in the soil mixture.

Hmmm. I wish weighing would work, but I don't know if it would for what I want to do.

kimmsr, you don't really come out and say it, but I assume you are saying that there is not a model at $100 or less that would be close to accurate, is that correct?

I could try to do what I am doing through volume....but not sure how that would work, either. But, it may be the only way I can.

I'm not sure what kind of number you need. If you saturate and weigh the sample, dry it in an oven and weigh it again, you can subtract the second number from the first and you will know exactly how much water the media was holding. The results will be as accurate as the scale you use.
Then you can use those numbers to figure out the percent moisture on a dry weight and saturated basis by dividing the weight of the water by the weight of the dry sample and then dividing the weight of the water by the weight of the saturated sample.
Or you can let it drain for a couple hours after saturating and do go through the same process to find percent water from that point.
If you measure the volume of the container you're using, you can calculate moisture holding capacity and air space.
There are lots of things you can figure out just by weighing, drying and weighing.
Is that the kind of stuff you're looking for, or something else?

OP wrote "Hmmm. I wish weighing would work, but I don't know if it would for what I want to do."

So, what is it you want to do? We could give better responses if we knew.

I haven't thought it through completely enough to explain it. It's based on an idea I had from reading multiple posts over the years about watering and people's failure with plants. So I want to prove a concept and then find a simple way people could use to apply the rules that I determine - all related to how much to water certain plants.

BUT - just in typing that, weighing would work well because it would be easy for them to apply and using a meter won't. I think I want a meter so my brain can apply "how wet is that" vs how heavy is that. I think my brain wants to say X wet is too wet, but that won't probably help anyone else, just me.

Ultimately, I want to correlate X water to X wet to X results with the plant.

Not sure any of that made sense, I've just been up for 30 hours and am a bit tired.

"...X water to X wet to X..."

Can I buy a vowel?

Seriously though, if I had a nickel for every great idea I thought I had that I couldn't articulate well enough to be anymore than giberish, I'd be retired already!

Lloyd

weighing would work well because it would be easy for them to apply and using a meter won't.
I see where you're going, but consider X what type of planting media. And X what type of container. And X how does the size of the plant fit in. And X etc.

If somebody is using more or less perlite than you, that will change the weight.
If someone's mix has pumice and yours doesn't, that will change the weight.
If somebody is using an 80% 20% peat to sand and you used a 50% 50%, that will change the weight.
I'm not just talking the weight of the media itself but also the differences in weight due to the variation in water holding capacities of all those different things.
And what about people using hanging baskets or smiling ceramic turtle planters with top hats and walking sticks while your weights are based on a standard one gallon nursery container?

I'm not saying it's impossible, but that's a pretty tall order to fill.

When we did lab in undergrad, we knew exactly what mix we had, and we always used the same mix - standard UCD mix. If you can't standardize the mix, you can't do what you want, like gargwarb sez. Too many variables. And we had good scales, to the .01 mg. Then let's talk about temp. And RH. And EC. And ET of different spp. You can't control things outside your control.

Dan

"You can't control things outside your control."

Sage. ;o)

I'm lucky lately if I can control things WITHIN my control.

Al

(entirely good natured, Dan - a friendly poke in the ribs)

You are all right....but there MUST be some basic principles that people can apply...there MUST be. I just can't handle all this ambiguity!

I was assuming we'd be using the same soil mix. A forumla. And, yes, it would vary some based on how people mixed their soil, etc. But it has to be within a certain variance, doesn't it?????? You could create a rule that said if you use X formula, in X size pot, with a relative humidity in your home of between X and X, you will need X water the saturate your soil.

OK, take a recent example. I recently started growing African Violets. I'm an outdoor gardening, not indoor. I don't kill my spider plant, and my philodendron is happy, but that's not saying much!

So, everyone (you know, the AV community folks here and other forums) says you should use a 1:1:1 mix (and I won't debate that right now, but I imagine it's not best, but...) and it should be damp but not wet.

Well, what the heck is damp but not wet?????? No wonder people screw it up and kill the poor plants. There MUST be a basic set of rules that people can apply. Not people who won't read or think or weigh, I don't imagine, but people who are willing to put a bit of thought into applying the rule.

Am I asking too much?

there MUST be some basic principles that people can apply
In regards to what? You need to ask a specific question.

I was assuming we'd be using the same soil mix.
People use all kinds of different stuff depending on what is available regionally, what they are willing to spend, what plants they're growing, personal experience, and what they have learned from other sources.

But it has to be within a certain variance
What has to be within a certain variance? The dry weight of the material? The saturated weight of the material? The moisture retention curve? The percent air space? The time required to dry? Etc.? Besides, even if you could identify a point where one of those or any other variable falls within a certain range for all possible soil mixes, that doesn't mean that the point where they all meet would be suitable for plants.

So, everyone (you know, the AV community folks here and other forums) says you should use a 1:1:1 mix
What materials do you have in mind? Peat: perlite: sand? Coir: pumice: vermiculite? Sand: bark: compost?

So I want to prove a concept

What concept? You won't even tell us what you're trying to do, but you want us to fix your problem for you. And I mean specifically what you are trying to do, not just "tell people how to water their plants".

This thread has certainly changed from the first post. Originally it sounded like you had an idea but you just needed to know how to measure soil moisture. We were very welling to help you do that, we just needed to know exactly what sort of numbers you were looking for and we would be off to the races.

Since then, it's gone to "I want to give the world a set of universal rules to use but I have no idea what those rules would be. Design a one size fits all mix for me, tell me how it will work for every plant in every situation and don't confuse me with the fact different materials, at different volumes and ratios, behave differently so that I can be an expert.

but there MUST be some basic principles that people can apply...there MUST be.

Holding your breath and drumming your heals on the floor won't make it happen.

I realize that you're frustrated and that the ambiguity of our replies is upsetting you but if you look at your questions, you'll see that they are the source of the ambiguity. It's difficult to give you specific answers when you won't ask a specific question. You can't ask vague questions and expect the answers to be any less so.