In my quest to firmly grasp the art of bonsai, I’m eager for any tool that will help add a dollop of science to the art form.
Through the years I’ve been dabbling I’ve lost a lot of bonsai, and I believe most plants that have died have been from over or under watering. There are plenty of other potential trees I’ve killed for other reasons, but watering is probably the leading cause. Going on vacation and loosing half of my material to someone else taking over the watering is included in that ratio and accounts for at least half of those losses though so I’m not that terrible.
In my humble opinion there is a good amount of ambiguity in understanding if a plant’s water needs have been met. I’ve tried touching them and scratching down a little into the soil. Which has given me dirty hands, dirty nails, and lots of little holes in my pots but hasn’t always given me a black and white answer.
Hence, this test on moisture meters. For about $20 having the ability to see as much as possible in a black and white number how wet or dry my plants are and match that to any list of plant preferences sounded like a very good thing.
Lets get started! First understand that there meters for measuring moisture levels in soil and those for measuring the moisture levels inside of wood. You want the plant kind. The other kind will be completely unhelpful. Next plant moisture meters are often combined as a 2 or 3 in one feature with sunlight and pH readings. That’s a personal preference we’ll discuss those features later.
Last, for the two meters that test beyond moisture, misreading the meter is one of those things that are easy to do by not following simple directions. It’s easy to forget to flip the switch from reading light to reading pH or miss really any of the easy directions. (Leaving moments where you say EH! This thing is broken! It isn’t worth crap! Then some time later you realize you, ahem, forgot to turn it to the right setting. Oops.)
Here are my findings:
I tested the four most popular moisture meters I could find. Two were from Amazon, two from Home Depot. If you look, several companies sell the same kind of moisture meter. Though I tested a plain moisture meter called “Dr. Meter” I can also find a suspiciously identical meter being sold by one or two (or three) others. I’m sure this is the same product, produced in the same factory, by the same people, of the same materials. But contracted by different people and thus with different labels on the product.
Water Check Soil Tester by Greenscapes
PRICE $9.99 (for a pack of three)
APPEARANCE: These meters are basic green plastic sticks that look like there’s a strip of paper or something similar inside, with a clear plastic covering on top that has a few ridges or lines to help you understand where to position the meter correctly in the soil. This one is decidedly for the low-tech crowd.
BASIC OPERATION / HOW TO USE IT: These meters are different from the other three because you put them in the soil and leave them, whereas the other meters you put in the soil, read, and remove. You simply insert one of these meters into the soil to the level noted on the back of the card (which is based on what type of plant we’re talking about, junipers would be different than cypress for example). That’s it. Water your plant and you’re done. The color of the strip indicates when you’ll need to water again. Dark green means don’t water, white means do water.
FINDINGS: They’re cheap, with a box of three costing me about $10. In this way you can have a meter that stays in the pot you can leave there all the time for $3-4. The meter doesn’t quantify like the others though, at times its more of a condensation filled gray strip, so it takes some time to get the knack for, and it’s up to you to decide if you can read the meter more clearly than, say, a popsicle stick. One advantage to the meter though is that for larger pots such as pre-bonsai you get the water reading at the root level, and for smaller bonsai you at least avoid sticking your fingers down into the soil mix over and over again making lots of holes.
Soil Master by Mosser Lee
APPEARANCE: This meter looks like, well, like a green box on a stick. There’s a basic window with a single simple chart where a needle moves from dry to moist to wet based on the moisture level of the soil. It has a one-year guarantee from the manufacturer.
BASIC OPERATION / HOW TO USE IT: To use it simply insert the metal tine into the soil halfway between the plant and the wall of the pot, to ¾ the depth of the pot. Place it in the soil, wait a few seconds and poof: moisture reading. If the color chart was not obvious enough the back operation card takes that one higher. Red is dry to slightly moist for plants that like dry conditions. Green is slightly moist to moist for most indoor houseplants. Blue is “very moist. Do not water. Do not drown your plants.”
FINDINGS: The meter nicely quantifies moisture or dryness in a way that’s a step up from the green sticks. You can read clearly in a numerical way how wet or dry your plant is. It is though just a moisture meter that does only this one task. How much you like either of those things is purely up to the user.
APPEARANCE: This meter is oval shaped and made out of plastic, supported by two tines. There is a clear window showing a black paper depicting three curves: meters for light, moisture, and pH. The bottom of the meter has a basic switch labeled moist, light, pH.
BASIC OPERATION / HOW TO USE IT: To use simply put the switch on whatever measure you intend to read (moisture, light, or pH). Insert the tines into the soil close to the plant and pot, with the tines at root level (or deeper for pH). Compare moisture or light to your plant’s requirements in the chart listed on the package.
FINDINGS: This meter has the same advantages as the previous meter and adds other features. I found the addition of being able to measure pH and light to be helpful myself, and feel that for a few extra bucks it’s worth it. But that depends on the needs and preferences of the user. As a side note there’s a lot going on in a little space here. Any user who likes big picture books or large fonts on their computer may not like this product.
Also the pH meter is positioned on the bottom of the needle gauge. This makes it a very small incremental difference between, say, a 5.5 or 6 pH. The numbers are small and there’s such a small space difference between different levels If you’re really interested in precise vs. ballpark pH readings or are tinkering with the pH of your soil mix and thus are making small adjustments and checking the results this may not be the device for you.
APPEARANCE: This Dr. Meter product is oval in shape and black and yellow in color at the end of one metal tine. This meter was the only one to need batteries because it is digital (which were provided in the package). There are two buttons one simply reads “ON” and the other “C/F and OFF”. There’s also a switch in the back on the top that changes from pH reading to temperature reading.
BASIC OPERATION / HOW TO USE IT: This one claimed to have four in one, a unique ability. The fourth component is that it tells the temperature. To read, press the “on” button, switch the back slide to the what you want to read, insert into the soil, wait several seconds, and read.
FINDINGS: This meter had the same capabilities as the last meter but the digital nature changed the effects to some degree. I preferred this product to the other in terms of a clear pH reading. You numerically get a number that is large and easy to read. There is no ambiguity if the meter is reading 6 or 6.5. Like many digital products this meter was hard to read at times depending on the light (the sort of thing where you see all the numbers as grey). But at other angles that problem disappears with no problem. With the disadvantages, you also get the advantages of digital. On the downside this meter only tells you if your soil is dry, normal, or wet, which is less data than you got from the last two meters which show you a quantifiably scale.
One nice thing about moisture meters is that three of the products quantify in clear numerical or black and white where your plant stands on moisture. For those that have a tendency to overwater this can be helpful. It clearly shows when to stop watering your plants and also helps show if your watering is reaching the roots or just watering the surface. This is true for all meters. It also keeps little finger holes out of your pots.
The manufacture of each instructs the meter to be removed and wiped clean with a cloth after each use. The meters are not supposed to be left in and may not work in time if they are. If you water you will need time after you water for the soil to absorb before retesting.
Tine tips have been known to break off of these meters, so check yours periodically to see if it’s loose before inserting and be careful when inserting into hard ground, you may need to use something else like a chopstick to break up the soil first.
The light features don’t tell you how many hours of sun your plants are getting, just what the light conditions are at that moment. Though the third meter does quantify the light your getting, which can be helpful to see on a spectrum how dark “shady” is and how light or bright it is.
The monitors work by a level of friction against the tines, which is why monitors wouldn’t work in a glass of water. It means they also may not work in a bonsai soil mix composed of largely inorganic materials. The later three meters may be better for periodic assessment of pre-bonsai and growing stock rather than finished bonsai. They’re also for use in standard household flowerpots. Those with larger trees found in the wild should know the tines are roughly about ten inches in length. If your root mass is much deeper than this you won’t be able to see if the moisture is getting to the bottom of the root mass, only to the bottom of the tines.
I advocate the first three for use in pre-bonsai, not bonsai. Many bonsai pots were difficult to measure because there just isn’t much space for the tines to sink into, and though I believe my soil mix was reading and working fine, I’m not sure how many more percent inorganics in your mix would cause them to not work. For those wanting to use a moisture meter in their bonsai you might consider the first set of meters.
That or you could just use popsicle sticks.