Indoor plants are notoriously tricky to keep healthy and alive, especially in winter. You’re attempting to replicate a complex and naturally accommodating biome inside your home. Plants that thrive in nature wither on your countertop, and sometimes, it’s really difficult to pinpoint what it is you’re doing wrong.
One of the most common culprits is moisture. Not only do individual plants’ needs vary, but if you see a problem with a plant, the first (over)reaction is often to water, which can lead to overwatering, or pulling back on watering, which can lead to dehydration.
I myself am certainly guilty of this habit cycle, so I figured why not buy a moisture sensor and see if I can build a watering schedule based on actual data: Would my plants benefit? Could a cheap soil sensor help me rescue the orchid on my kitchen table that’s been struggling for weeks?
How soil moisture sensors actually work
Common capacitive soil moisture sensors rely on the electrical properties of the materials they’re built from. Typically, they consist of two conductive surfaces separated by a nonconductive material, called a capacitor.
Dry soil acts as a dielectric, a substance that is a poor conductor but can hold an electric charge. That ability to store a charge grows as moisture levels increase, which affects the capacitor’s electrical properties. The sensor measures the dielectric constant. It then translates it into a percentage, number or, in the case of the $13 sensor I got on Amazon, a simple reading from a gauge with a range between 1 (dry) and 10 (wet).
The length of the probe on the sensor I bought is a nice advantage, as it allows me to read the soil moisture level all the way to the bottom of even very deep pots. This is crucial because roots can pull differing amounts of water from the soil throughout a pot, and soil may be saturated during watering differently at different depths.
Let data tell you when to water
Prior to this test, I was relying on the typical indicators of when to water. I tried to follow a schedule with most of my houseplants, even as I accumulated plants with different needs that needed to be watered at different frequencies. I also relied on anecdotal evidence, like the finger test, where I tried to feel how moist my plant’s soil was, or by testing the weight of the pot or watching for signs of withering or dryness in the plant itself.
The problems with these methods are numerous. For one, I have a garbage memory. Remembering to water on one specific day was difficult enough; having to remember multiple schedules for multiple plants was untenable.
The “anecdotal evidence” approach wasn’t much better. Unless you’re poking a finger deep into the soil at different spots all over the pot, you’re not getting a holistic sense of the moisture, and surface moisture can be deceptive. Also, importantly, human beings can’t technically sense wetness.
Reading the weight of a pot was guesswork at best, and often by the time a plant starts showing distress, it’s too late.
Enter the sensor. Once I got my unit, I started tracking moisture drop-off over days. I also tried to keep an eye on how different plants were drying out not only at different speeds but at different depths within their pots. I logged daily results for each plant in a notebook I bought specifically for the purpose so I could track changes over time.
Most of the early results weren’t surprising. The top few inches of soil dried out faster than deep soil, which stayed moist for much longer.
Also, in the early going, it was obvious how much soil type/composition mattered: The fast-draining, gritty soil in my succulent pots dried out a lot faster than the richer soil in my tropical plants’ pots.
The results after several weeks
I’d love to say that I rescued some plants that were yellowed and on the precipice of death, bringing them back to verdant life, but the reality is none of my plants were in that desperate shape. I just wanted a consistent way to avoid over- and underwatering and to build a reliable schedule. In that regard, the sensor was a resounding success.
By taking readings in every pot for a couple of weeks, I was able to get a sense of how quickly moisture drained out of each pot. With that data in hand, I built a solid, data-based watering schedule and built calendar reminders for myself based on what I learned.
Three weeks in, I’m seeing improvements, particularly in the aforementioned orchid. Orchids are notoriously fickle about watering (and hold water quite differently at different depths).
Properly watering has led to new leaf growth, and I’m even seeing buds sprouting on it for the first time since it initially shed its flowers many months ago. The air roots look greener and healthier, and the leaves themselves are waxy and firm. (They were quite droopy prior to this experiment.)
I’ve also seen fewer yellowing leaves on some of my other plants. In general, I’ve seen a strong improvement in consistency. Whereas before, while some of my plants looked a bit ragged while others were relatively thriving, now all of them appear healthy and well maintained.
While I’ll continue to check using the sensor occasionally, the nice thing about this experiment is that I now have a reliable schedule. So until I introduce new plants, I won’t need to continue to measure every day.
That said, the most surprisingly pleasant outcome of the entire experience was rather unexpected: confidence. Instead of the scattershot approach I was taking before, which left me feeling uncertain and sometimes even a little guilty when I watered (or forgot to), now I water my plants with confidence. I know I’m doing the right thing for their care and contributing to their health instead of guessing at it, and it’s hard to overstate how much I enjoy the entire process more as a result.
In the end, it was worth it
So, was it worth the price and hassle? For me, the answer is a resounding yes.
Not only was the initial investment a really low bar, cost-wise, it also didn’t feel like much of a burden to run the test and track the results. In fact, I had a lot of fun, noting differences over time and between plants.
The analog sensor I got, though cheap, provided reliable, consistent readings and was a breeze to use. Just stick it into the soil to the depth you want to measure, and it immediately displays a result.
Again, the real benefit is confidence. I not only have a better sense of how much water my plants need and when, but I feel much more secure every time I fill up the watering can.
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