Ask a Question forum: Moisture gauge

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Name: Melissa
Paradise, CA (Zone 9b)
Aug 13, 2016 11:39 AM CST
I have a moisture meter I bought at a nursery last summer; they said it would help me judge when and how much to water. Another nursery told me that it was a waste of money and I should just throw it away. Does anyone have experience with using one? I usually just stick my finger in the soil to check for dampness, but with over 20 container plants, it gets tiresome. What do others here think about it?
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Name: Elaine
South Sarasota, Florida (Zone 9b)
The one constant in life is change
Cat Lover Master Gardener: Florida Tropicals Multi-Region Gardener Vegetable Grower Region: Florida
Herbs Orchids Birds Garden Ideas: Level 2 Garden Sages Celebrating Gardening: 2015
Aug 13, 2016 12:45 PM CST
I have one of those too, Melissa. I'm firmly on the "waste of money" team just because what's right for one plant is wrong for the next as far as moisture goes.

You can also have a plant that's dried out too much, but when you water it the water just whizzes right through the pot and isn't absorbed. So your moisture meter would tell you the soil was bone dry even though you watered the plant 5 minutes ago. It takes a good long soak in a bucket to re-hydrate dried up potting soil.

I used it for a short time and found it really didn't tell me anything I needed to know, and sometimes told me wrong information. Your fingers will tell you more.

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Foliage Fan Xeriscape Container Gardener Bromeliad
Hummingbirder Native Plants and Wildflowers Garden Photography Region: Mexico Plant Identifier
Aug 13, 2016 2:31 PM CST
Those meters are excellent and reliable, within reasonable limits. I used mine for a while to get an idea of how fast pots dry out. At this point I don't need it any more because I have learned through time and experience. You don't want to be jamming one of those in the soil every time you water because they will do damage to the roots over time. Once you get a sense of how things work, the meter renders itself unnecessary. You can calibrate the readings to your finger readings, or better yet wait to repot one of your plants until it is dry or nearly dry (pick the setting, wherever you want them to end up), then confirm the meter is reading a moisture level that agrees with what you can see with your own eyes.

There's no reason to fault the meter for one plant having different needs from another. And there's no reason to fault the meter for not watering thoroughly (to completion). My plants are almost all succulents and I let the vast majority go dry or mostly dry, every time. You don't ever need to soak pots in a bucket to rehydrate dried out soil. Instead, water in two or more passes, separated by a few minutes. The first pass, the soil gets a little bit moist. Then the second pass it can absorb more water. Once you get an idea of the holding capacity of any given container, you can be pretty efficient doing this. The reason it makes a difference is that peat (like other organic fibers) does not absorb water efficiently when it is bone dry, only when it is moist.

If you want to test this, you can try an experiment. Allow a given pot to dry out all the way. Then water it until water comes out the bottom. Try not to pour on too much excess water, so the results will be easier to interpret. Allow that water to completely exit the bottom of the container into a saucer, and move the container to a new dry saucer. Take a 5 or 10 minute break. Then come back and pour that water (plus whatever may have seeped out during the break) back on top of the soil. How much of it gets absorbed? How much passes through the second time? You may be surprised by the results. They will be more dramatic in larger pots.
[Last edited by Baja_Costero - Aug 13, 2016 3:01 PM (+)]
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Name: Val
Near Boston, MA (Zone 6a)
Aug 14, 2016 3:45 AM CST
I have a tendency to overwater, so this is kind of a lifesaver for me. I've grown clematis from bare roots and tend to overwater while in pots. This moisture meter has helped me not to do that. For my standpoint, it's a keeper. If you have alot of pots, things can also look dry on the top. It will tell me if it really needs watering or not.
Name: Melissa
Paradise, CA (Zone 9b)
Aug 14, 2016 8:59 AM CST
One thing somebody told me once has always helped me when watering. Think,of the soil as a dry sponge. When dry, it won't pick up anything spilled on the counter. But once you wet it, it easily picks up spills. This is akin to watering a dry plant just once. The soil is too dry to absorb much of the water. But when you do a second pass, the soil is moist enough to absorb as much as it needs.

I like the idea of using the meter as a comparison to my finger. When my finger says "water me," I can then use the meter and see if its results are the same.

I too tend to overwater. I'm hoping the meter might help me learn not to.

I'll let you know how my comparison goes.
Name: Will Creed
Professional interior landscaper
Aug 14, 2016 11:14 AM CST
I used moisture meters for several years before realizing I was allowing the seemingly scientific readings to overrule my common sense. Then, I learned that these devices do not really measure water content. They measure electrical conductivity between two different types of metal on the probe. It assumes that water is the only conductor of current and that is not true. Plants in soil that is very dense or high in mineral salts will cause the meter to read higher than it should. Very porous and some sandy potting mixes tend to read very low. If all your plants were in the same potting mix and the mineral content (water quality, fertilizer) was consistent and carefully controlled, then these meters could be reasonably accurate. But that is rarely the case. My advice is to trust your experience and common sense and not be overruled by a pseudo scientific technical device.

I do use an inexpensive plastic soil probe (Soil Sleuth) that does allow me to pull tiny bits of soil from deep within a pot and see just how damp the soil is up to a foot below the surface.
Will Creed
Horticultural Help, NYC
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Foliage Fan Xeriscape Container Gardener Bromeliad
Hummingbirder Native Plants and Wildflowers Garden Photography Region: Mexico Plant Identifier
Aug 14, 2016 1:04 PM CST
There is nothing pseudo scientific about using conductivity to measure moisture in soil. That's how the device works. Did you actually see it measure differently depending on the type of soil? What specifically was the difference? Obviously one has to calibrate these devices against some other observation. But in my mind measurements are always going to be better than common sense, unless of course you employ both. Smiling If I were forced to choose, I would prefer careful observation to common sense any day of the week.

For the record, my plants are in the same kind of mix and I do not vary my water supply, so those are quite relevant assumptions. You can easily test the difference between two mixes or two sources of water using the device, to the extent they actually exist. That's the advantage of being able to rapidly test two things side by side using something that gives you a result in 2 seconds.
Name: Daisy
Reno, Nv (Zone 6b)
Not all who wander are lost
Garden Sages Plant Identifier
Aug 14, 2016 1:34 PM CST
I think moisture meters are great. I use them all the time but after I figure out my plant, I don't need it until the next new plant. On the other hand, if you haven't re-potted in quite a while, the meter could be measuring salt build up in the soil.
Name: Carol
Santa Ana,Ca. (Zone 10b)
Sunset zone 22
Charter ATP Member Hummingbirder Lover of wildlife (Black bear badge) Orchids Region: California Plant Identifier
Aug 15, 2016 3:27 PM CST
I too have many pots to water, and I do use a moisture meter often, but not always. I use Baja_castro's method and instructions for the most part. some pots are always going to need water, but others are easy to over water. Depends on potting medium, size of pot, and how root bound the plant is. I have found that the meter doesn't work well in a chunky medium like orchid bark or gravel. I also use my meter to judge when the lawn and flowerbeds need water.
Name: Melissa
Paradise, CA (Zone 9b)
Aug 18, 2016 10:31 AM CST
Well, I've been comparing the moisture I feel with my finger, and with the weight of the pot, to the meter, and they match pretty well. I haven't tried Baja-Costero's idea yet, but I will. I've just been too depressed to go out and get the saucers. Sad I'm planning on doing that this weekend. Will let you know how it goes.

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