There are a TONNE of articles on whether pebble trays work, some said they do and others say they don’t.
I had to try it for myself. I can’t go around recommending humidifiers to people when they could get the same results with some gravel and a pasta dish.
Also, I may as well give it a go. I have gravel and a pasta dish.
My experiment determined that pebble trays don’t work. At least, not to any discernable degree.
Humidity and light are GAMECHANGERS when it comes to plant care. Get those two things right and plant care will be SO MUCH EASIER.
What are pebble trays?
A pebble tray is a shallow tray that you fill with, er, pebbles and water.
The principle behind them is that you sit a humidity-loving plant on the pebble tray and the plant can absorb the surrounding humidity caused by the evaporating water.
I have an article here on why humidity is so important to many houseplants.
The layer of pebbles keeps the plants out of the water, so you don’t end up with root rot.
Why use a pebble tray?
They can be aesthetically pleasing
I’m one of those people that doesn’t have an Extra Stuff, because I’m not great at dusting, and the fewer things that collect dust, the better.
I’m also a bit clumsy, so having dishes of water and pebbles everywhere is a disaster waiting to happen.
However, I’ve seen a few photos on Pinterest of people incorporating pebble trays into their home decor and it looks really nice. My preferred style can be best described as ‘Scandi but 70s’ so I definitely could make a pebble tray work, it especially fits with the ‘Bohemian but add crystals’ vibe (which I love, but would NOT keep tidy).
They’re cheap to put together
For those of us that aren’t prepared to fork out for a humidifier, a pebble tray is a cheap option. You know, if they worked.
The problem with using pebble trays
I mean, aside from the fact that *spoilers* they don’t really do a lot
Things like them being messy and not particularly practical aside, any standing water in your plant room can quickly end up being a fungus gnat nursery. If you live somewhere with a lot of mosquitoes, you can also end up with mosquito larvae*.
*If you keep fish, they go WILD for mosquito larvae. One person’s nightmare is another’s money-saving tip!
The experiment
I filled a pasta bowl with leca (I’d have gone outside for gravel, but it’s raining and I’ve not got dressed yet because I want to clean my house later and there is NOTHING like working in your pjs, then cleaning your whole house, then showering, putting on fresh pjs and sitting in said clean house. And I have to do a good job because my parents are coming for coffee this afternoon.
Anyway.
So yeah, I added leca to a bowl, and added water.
First I measured the humidity of the room sans pebble tray:
Then I added the pebble tray:
I left it for a bit for the pebble tray to do it’s thing, and…it went up! By one percent. Hmm.
However, my hygrometer is much shorter than my plants, so I thought I’d see if the humidity was lower as we moved away from the water…
It went up again! So then I removed the pebble tray to see how much humidity the tray was generating by itself and:
I left the hygrometer on the plant for hours, and it went up to 72%. I then put it back on the pebble tray and it went down to 71%.
The issues with the experiment
Humidity naturally fluctuates
We can’t tell if the humidity would have fluctuated regardless of whether there was a plant or pebble tray there.
We don’t know how accurate the equipment is
I only have one hygrometer (though I used a brand-new one). If I were a proper scientist I’d have used a few. I would also have found some way of calibrating it.
I have naturally high humidity
Does humidity increase faster in dryer conditions? I don’t really know. Here’s what Google had to say:
Nothing. The top comment was how drying clothes in low humidity and high temperatures is easier. I already knew that.
Perhaps we’ll never know. If anyone has low humidity, would you please try the experiment so we can see if pebble trays work better when the ambient humidity is lower than, say, 50%.
So, do pebble trays work?
Not to any discernable degree. One degree higher humidity isn’t gonna make that much of a difference.
However, what we can say is that your plants create a slightly more humid environment. By, again, 1%. Never mind.
The room I tested this in is fairly small – it can technically fit a double bed in it, but there would be no space around three of the sides and a pathway about 1m wide. Smaller rooms exist, but not many. So this is pretty much a best-case scenario – pebble trays would have even less impact in a larger space.
What’s more effective for raising humidity, pebble trays or misting?
If you’re looking to increase humidity, that’s like saying what’s a better way of disciplining a child: hitting them, or shouting at them.
Both methods have been used for years, but neither is effective, apart from in the very short term.
I’m actually quite proud of that analogy.
The most effective way of increasing the humidity in a room is to buy a humidifier. The one I recommend is on my resources page.
But what if only one of my plants needs high humidity?
In this case, buying a humidifier is possibly overkill. A better option would be to put the humidity-loving plant in a terrarium. We use an old aquarium, but you can use anything that’s big enough and clear. Plastic boxes are perfect.
Pebble trays aren’t particularly good to use in terrariums because they end up spilling. You’re better off using a substrate that retains water, which is why sphagnum moss is a popular choice.
Damp substrate and a small space can really quickly increase the humidity. Adding a heating mat underneath can raise the humidity even faster. Remember to add more water when the humidity starts to decrease.
Final thoughts
This was hardly the perfect experiment, but it did seem to show that pebble trays have a minuscule effect on the humidity of the area around them.
They would be more effective in warmer temperatures, but since humidity spreads out, it still would struggle to have a significant impact on the humidity of a whole room.
