Horti - Sure, I'm happy to elaborate.

Yes, moisture meters do work in gritty/porous mixes, but maybe not in the way you would expect. All of them essentially rely on sensor contact area, which can vary depending exactly how the probe went in.

The instantaneous number is not helpful alone, unless you know the moisture trend for that particular location and sensor. Ability for plants to absorb water roughly follows a decaying exponential curve, which is very predictable.

So if you want to use a moisture meter, I recommend sticking it in one spot and monitoring it for several weeks. Even if you don't have a logger, you can build a correlation between when your plant needs water (by observing its leaves) and the moisture value given.

Once you get a feel for the numbers, then you can get into the habit of "watering the day before it's required". With this knowledge, you can better maximize your plant's growth potential. That is, you can anticipate your plant's need before it has to display drought response.

It works the other way around as well. Things have been too busy and I know I am now 2 days past due for watering:

1. 1 day past will result in slightly shriveled leaves, lost growth opportunity.
2. 2 days past will result in leaves being absorbed beyond point of recovery (lost leaf for many plants).
3. 3 days past will result formation of air roots.

My Crassulas, Haworthia, and some Mesembs are most notably suffering, so tonight I HAVE to water. I know I will lose one leaf from my Haworthia 'Tenac', which makes me quite sad:

Weight to determine when to water is pretty effective. A couple of my pots are in natural light only and I am not monitoring their moisture. Handling those pots is the easiest way to check moisture levels, along with plant response. Those plant are not as important to me, so I am not so picky in making them flourish.

I believe the Parrot Flower Power uses dielectric constant/capacitance for EC measurements. This is because the device requires several full waterings before reporting EC levels. My assumption is that it is performing a calibration on the soil medium during that time (which is the preferred method).

For my succulents, the soil EC meter is not so useful because my target is around 0.06mS/cm. It's hard to read anything below 0.1mS/cm with the soil EC meter. Therefore, I am occasionally checking my substrate EC with the Pour Thru method and a liquid EC meter.

I fertilize every other watering, which helps smooth out the available nutrients in my soil mix. Otherwise it's a larger swing between nutrients provided and leeching out by watering. This is measurable with my soil EC meter and my liquid EC meter.

This fluctuation is shown in a graph in my second post of this thread: Succulents Before and After 6 Months

For my outdoor garden plants my target was around 2mS/cm and the soil EC meter was very helpful because for that I use water-soluble powder that fluctuates greatly after big storms/heavy rains.

Wish I could say more definitively how the moisture/soil EC sensor works in my device, but the algorithms/sensors seems proprietary. The different sensor technologies measurement units, and significance of them are not so straightforward and not many people are discussing them online (probably due to cost).

Hopefully that helps answer some of your questions and you didn't get too bored reading my response. =)

Personally, I have never found moisture meters to be of much help. (Mine is packed away in a box somewhere.)

I rely on my own sense of touch, on wooden skewers combined with my sense of touch (pressing it to my cheek), or on a combination of my senses and the weight of the pot... as I've come to know from experience. You get a feel for the approximate weight of an individual pot, before and after watering thoroughly.

The beauty of using a more porous, sharp draining medium like the Gritty Mix is that there's little chance of over watering. I, myself, utilize the Gritty Mix for my indoor plants, and something closer to the 511 for containerized plants grown outdoors.

That's not to say that a meter can't work for someone... but for me, it was more of a waste of money.

Jodik - I totally agree that a keen observational eye and sense of touch/handling pots is an essential part of being a good grower. No meter replaces that, regardless of what the manufacturers may claim.

Cost-wise, many meters and tools are quite expensive and I understand most growers would never be willing to spend or justify the money. They are definitely not something a casual grower would typically even consider (Added note: I do not consider you a casual grower).

For me, it was curiosity and focus on taking my knowledge much further than I thought was possible through just reading/discussing with others.

In my work, taking what others have said/done without fully questioning it is dangerous and possibly a major risk to the public/environmental safety. So I think this same approach has trickled down into my personal life and hobbies. =)

Thanks so much for the detailed response, ewwmayo.

The Parrot model seems very multifunctional (and quite a varied product mix from the company, though suppose you can use the drones to deliver water to the plants when the meter requests it :)

Was interested in dielectric-constant tech as I noticed it was used for spot metering moisture in grain and rice (which seemed more grit-like than in-ground garden soil where conductivity sensing may make perfect sense). But the only other probe that seemed close to a consumer price range was from someplace called Vegetronix.

Guess you'd specifically center the probe at the depth of the main root zone. I've found that the first couple of inches of gritty mix will at least appear very dry, very fast in a very low humidity, heated indoors.

Have to say your charted moisture levels do seem quite usefully regular (especially indoors). And don't think I'd trust in-soil EC (for nutrients), in any grit-based mix either.

Again, your posts are much appreciated.

edit: PS noted that at least one re-seller and one review list the flower power moisture probe tech as dielectric.

Hi jodik, Admittedly some appeal is just fun-with-tech, but still considering myself a beginner with gritty mixes, also was thinking I might be interested in an additional impartial measurement - for now - to help hone my feel for plants and the medium. (And have no illusions about the accuracy or reliability of low-cost consumer-level tech.)

Been slowly switching things over to gritty, and learning as I go . . . but gotta say the plants seem happier.