9 DAYS AGO • 4 MIN READ

🪴 The finger test is broken (here’s what actually works)

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Houseplant Digest Newsletter

One weekly email with tips, tricks, guides and discussions around our favourite thing – houseplants!

The finger test is broken (here's what actually works)

Rich here, and welcome back to Houseplant Digest, sponsored by Houseplant SOS.

In this week’s issue:

  • Your finger has been gaslighting you this whole time
  • Why World Water Day matters for your windowsill jungle
  • The real science behind how plants drink
  • A three-part watering series kicking off this week
  • Did you know plants can "tell" each other they're thirsty?
  • And more...

🇬🇧 Sheffield Answers

Every week, I get tons of questions about growing houseplants. In “Sheffield Answers”, I’m going to pick one out each week and answer it. Want to submit your own and get it featured next week? Click here to ask me a question!

Question: When you first transfer plants into pon from soil how much water do you put in the reservoir? How far up the pot should the water go? Karen

My Answer: Aim for a third of the way up the pot and remember to top it up before it runs dry. Some plants seem to drink it up quicker than others. My spider plant needs topping up twice a week, for example.

🪴HOW TO & TIPS

💦 World Water Day

Yesterday was World Water Day, and while the rest of the planet was busy thinking about rivers, rainfall, and conservation, I figured there's no better time for us to turn the lens inward and ask:

Are we actually watering our houseplants as well as we think we are?

Spoiler: most of us can do better. And this week, we're going to fix that.

Starting Wednesday, I'm running a special three-part watering series. Emails will land Wednesday, Friday, and Sunday, each one covering a watering tip that most houseplant owners have never tried but absolutely should. Wednesday's in particular is one I think will genuinely change how you approach watering. Once you hear the logic behind it, you'll wonder why no one mentioned it sooner.

But first, we're kicking things off right here, right now, with a topic that might ruffle a few feathers: the finger test, and why it's less reliable than most people think.

☝️The Finger Test Is Less Reliable Than You Think

Now, I know what you're thinking.

Rich, the finger test is houseplant 101. You stick your finger in the soil, if it's dry you water, if it's damp you don't. What's the problem?

And look, I used to think exactly the same thing. For years. And my plants were mostly fine... until I started paying closer attention and realised they could be a lot better.

Here's the thing: the finger test isn't wrong, exactly. It's just incomplete. And for the plants that are most prone to root rot (your Monsteras, your peace lilies, your fiddle leaf figs, I'm looking at all of you), "incomplete" can be the difference between a thriving plant and a sad, yellow, sulky one.

So, what's the actual problem?

When you push your finger an inch into the soil, you're only sampling one small section at the very top of the pot. That inch near the surface dries out significantly faster than the bottom two thirds of the soil. It's a bit like checking if your bath is cold by dipping a toe in at the very edge of the tub. You might feel perfectly comfortable until your foot touches the floor and it's absolutely freezing.

A plant's roots don't sit at the top. They stretch down to the bottom of the pot, where moisture lingers much longer. So even if the top inch feels bone dry, the lower root zone could still be holding onto quite a bit of water. You water again, the roots sit in too much moisture, and before long you've got root rot making itself at home.

The variables that make the finger test even less reliable:

Soil composition matters enormously here. A chunky, well-draining mix full of perlite and bark will feel dry at the top within a day or two, while genuinely still having adequate moisture deeper down. A dense, peat-heavy soil can feel totally dry on the surface while being completely waterlogged a few inches below. Your finger can't distinguish between the two just from a quick prod.

Then there's pot size. A plant in a large pot relative to its root system is always going to hold water for longer than the surface suggests. I've caught myself watering a plant that the top of the soil told me was desperate for a drink, only to discover the bottom third of the pot was still holding water from the last watering five days prior.

And finally: pot material. Terracotta breathes, pulling moisture out from the sides as well as the top. Plastic and ceramic hold onto it. Same finger test, very different reality underneath.

What to do instead (or alongside):

The finger test can stay in your toolkit, it just can't be the only tool. Here are a few things that, together, give you a much more accurate picture:

First, lift the pot. This one's free, takes two seconds, and is surprisingly effective once you've done it a few times. A light pot means the soil is dry. A heavy pot means there's still water sitting in there. Over time you'll develop a feel for what your specific plant should weigh when it needs water. Call it intuition. Call it experience. Either way, it works.

Second, push further. Rather than one inch, try going two or three inches deep, or right down to the middle of the pot if it's a smaller plant. The reading you get down there is far more representative of what's actually going on at root level.

Third, consider a moisture meter. I know some people see them as a bit of a cheat, but honestly for larger pots or newer plant parents still developing their instincts, they're a worthwhile investment. They measure moisture at root depth and give you a consistent, comparable reading every time.

The finger test isn't going anywhere, and I'm not here to tell you to throw it out entirely. But treat it as a starting point, not a verdict. Your plants are trying to tell you what they need; the finger test is just one (slightly unreliable) translator.

📹 Watch & Grow: This Week On YouTube

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Did you know?

Through their root systems and underground fungal networks, plants can actually signal to neighbouring plants when they're under water stress, essentially sending a "heads up, conditions are tough" message through the soil. Your potted plants might not have that luxury sharing a shelf, but in the wild, they've got a whole communication network running quietly beneath the surface.

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Houseplant Digest Newsletter

One weekly email with tips, tricks, guides and discussions around our favourite thing – houseplants!