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Giving plants higher humidity makes a MASSIVE difference to the way they grow.
I want to scream it from the rooftops because it’s something that we talk about a lot, but it’s not something you can truly understand until you’ve, quite by accident, given your plant a shit tone of humidity.
It’s like giving plants steroids.
The only thing that makes a similar difference is light. I recently came into possession of a couple of nearly-professional grow lights and my plants are THRIVING.
If I could find a way to get 90%+ humidity under them, I would be very excited, but alas, no, my house would probably rot.
Why do plants need humidity?
Plants need humidity because they evolved in places that have high humidity. Plants that could use that humidity to their benefit thrived. They use water in the air to help with photosynthesis, which they need to stay alive.
As you can probably guess, plants that need high humidity but don’t get it can’t photosynthesise as well as they should be able to, and will struggle to grow well.
This is all very sciency and interesting. I get it. But what really excites me as a house plant enthusiast is taking a plant that’s getting the recommended 65% humidity and amping it up.
You may be sat there saying ‘Caroline, I don’t care’ BUT YOU NEED TO SEE WHAT IT CAN DO. A load of those questions people in the medium-game of plant care are solved by higher humidity (and better light).
How much humidity do plants need?
Some plants don’t need much at all. In fact, it can be harmful.
Plants such as cacti and other desert-dwelling plants can literally rot in too high a humidity.
But the vast majority of house plants hail from tropical rainforests and need an ambient humidity of about 65% to grow properly.
This massively varied from plant to plant, and even from one specimen to another.
I’ve also found that sometimes humidity can replace watering, and vice versa. For example, I don’t water my terrarium – I just keep it humid. Some ferns, even maidenhair, will tolerate lower humidity if you make 100% sure to NEVER EVER miss a watering.
I do not recommend this, because one late watering and your fern is a crisp.
There are some plants out there that die if they get lower than 90% humidity. Hilariously, those plants tend to be very rare and expensive, for example, Monstera obliqua. I simply will never have one. Too much responsibility.
What are the benefits of giving house plants lots of humidity?
High humidity can:
- help plants grow faster
- stop crispy tips
- you can go longer between waterings
- Leaves grow bigger
But are two other ones that happen if you massively except normal humidity which are VERY exciting:
1 – They start to activate their aerial roots, which means they start to climb by themselves
See what I mean by the medium game of plant care? Beginners are just trying to keep their plants alive, end gamers have a tonne of literal trees, and then there’s us in the middle trying to get out plants to attach to moss poles.
To demonstrate how 90% humidity activates aerial roots, here’s a frankly chilling photo of my heart leaf philodendron attached to the (plastic) back of my terrarium:
Aaaand here she is trying to attach to the glass at the front:
I don’t have to water moss poles, or wrap nodes in moss or anything. The plants just freaking DOES IT.
Heartleaf philodendrons don’t usually entertain aerial roots – they grow a millimetre long, realise the humidity isn’t enough, and shrivel up. Not in 90% humidity!
The second benefit is even more exciting!
2 – High humidity activates more growth points
I had no idea until my Rhapidophora tetrasperma started growing THREE NEW GROWTH POINTS AT ONCE. NOT INCLUDING THE ORIGINAL ONE.
This thing is now producing FOUR LEAVES A WEEK.
Is it too big for the terrarium and burning itself on the light? Yes, but that’s beside the point.
But look at the growth points!
And yes, it too has terrifying aerial roots.
How does low humidity affect plants?
If you have a plant that likes high humidity and you don’t provide it, it’s hard to get that plant to thrive.
Sure, some can live perfectly fine, especially those with thicker leaves, like Monstera deliciosa. Others will struggle – plants like Calathea and fittonia will throw hissy fits and generally sulk droopily.
It’s like keeping a plant in too dark of a space – it’s fine, but life is so much easier with a humidifier and a grow light.
If you don’t want a humidifier (or terrarium, which is how I maintain high humidity) and a grow light but you want thriving plants, pick plants that can make the best of that, like pothos.
By the way, I’d 100% go for grow light over humidifier BUT when I have the space for a MASSIVE terrarium, I’m definitely gonna get one.
Low humidity not only causes growth defects like brown spots on the leaves and leaves totally drying up, but it can also cause the plant stress.
Plants send out pheromones when they’re stressed (I think?! Or was that a dream?) and you can end up accidentally attracting pests like thrips and spider mites.
A stressed plant is in no position to fight off pests, which means that you’ll have to it quickly and without hurting the plant.
Chopping off the leaves is usually the only solution – if the plant was stronger, you could persevere with pesticides and neem oil for longer, but those things can damage a sick plant as much as the pests do.
What happens if plants get too much humidity?
As you’ve seen in the pictures, you can activate aerial roots and additional growth points IF you have the right conditions.
If you don’t have the right conditions, the plants can rot.
You need to maintain air flow and stop mould building up to stop rot. We actually have a live cleanup crew in our terrarium – healthy populations of springtails and isopods eats dead leaves nd fungus, generally keeping everything clean.
We have to keep the humidity 90%+ because we have a frog in there, so if plants die in there, it’s their bad luck – the frog needs his moisture.
We’ve actually never had a plant rot in there, though we did remove a maidenhair fern because the fronds browned from the misting. New growth came through quickly but it always looked half dead.
How to increase the humidity for your plants
The easiest way is to buy a humidifier. This Levoit one is the darling among house plant hobbyists.
I have an article here that lists 9 unconventional ways to increase humidity – drying laundry near your plants works really well!
Terrariums are an awesome way to increase humidity and can be as simple as a clear plastic box with damp substrate and a grow light.
It’s one of those aspects of plant care that’s talked about, but we rarely see just how much difference high humidity can make. IT’S A LOT.
Does misting a plant help with humidity?
In a terrarium yes, in a room no, not really.
Misting with a foliar spray is a good shout, and it can be a good way to keep plants dust-free, but misting does not replace humidity.
The reason it works in a terrarium is that you’re misting the substrate, and the water evaporates over time, resulting in high humidity. This only really works effectively in a small space.
Which plants need humidity?
Other than succulents and other desert plants, I can’t think of many house plants that wouldn’t benefit from higher humidity.
As I said before, most house plants come from humid parts of the tropics – even hardy plants like ZZs will benefit from decent humidity.
A lot of people consider humidity (and light actually) as being an optional extra. The only thing that plants really need is to be watered.
Actually, you’re better off sorting out the humidity and light. High enough humidity will keep the soil damp enough (plus plants can absorb water through the leaves) so that you have to water way less often.
Good light makes growing house plants…easy. Just shove ’em under a grow light and watch them go. The plants grow strong and quickly, and are better able to fight off pests and diseases.
If you feel like you’re constantly trying to troubleshoot what’s wrong with your plant, sort out the light and the humidity.
Which plants don’t need humidity?
Plants that live in arid conditions in the wild don’t need high humidity.
There are plants, like pothos and dracaena that don’t NEED high humidity, but you’ll struggle to get them to thrive without it. Once you do provide them with higher humidity, you don’t need to worry so much about watering them on time – they have an extra safety net.
Do you need a humidifier for house plants?
I don’t have a humidifier.
BUT the ambient humidity in my house is around 60%, so my plants grow FINE without one. I’d rather spend my money on grow lights.
However, I’ve seen first-hand just how much difference high humidity can make to plants (and exactly why you really shouldn’t put succulents in closed terrariums).
If you’re on the fence about getting a humidifier, high humidity is VERY beneficial to house plants, and if you have ambient humidity of 40% or lower you’ll massively improve conditions for your plants and widen the variety you’ll be able to grow well.