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The Ultimate Guide to Choosing a Humidifier for Your Indoor Plants

Humidifier, diffuser, air purifier, vaporizer...find out what they are, what they do, and how to work out what the best humidifier is to get for your indoor plants. Plus what water to use in your humidifier, how close a humidifier can be to your plants, which types of humidifiers are safe for house plants, what maintenance is needed and more. You might want a cuppa for this one. Ready? Let's go...  

 

Do house plants need a humidifier?


No, not all indoor plants need high humidity, but most prefer humidity above 50%Some are happy at the same level we are, and some tolerate dry air better than others. For hardier plants, the humidity of your home may be okay, no humidifier needed, especially in a typical humid New Zealand summer. 


However in some regions - and some times of year - humidity can drop down below levels many of our favourite tropical plants prefer. And below humidity levels we prefer too! Winter in particular can be a problem when most sources of heating create much drier air. If your humidity level often drops below 50%, or if you're seeing signs your plants are suffering from low humidity, a humidifier is worth considering for your plants health.


What humidity level do indoor plants need?


Humans prefer humidity around 35% to 60% for comfort and health. Heating in winter, and air conditioning in summer, can leave us with chapped lips, dry itchy skin and dry eyes when humidity drops too low. That's also why higher humidity is recommended for eczema, asthma and allergy sufferers, as when the air is too dry it can cause flare-ups.  


So that's our happy place, but what about our plants? Most indoor plants prefer humidity above 50%, however many of our favourite indoor plants come from tropical habitats where humidity is always above 70% (and that's in the dry season!). That's a far cry from the average 30% humidity of a heated home in winter. Poor plants.


However most plants would not have been selected to grow in huge numbers to be sold as indoor plants if they couldn't tolerate typical indoor conditions. Of course there is a difference between tolerate and thrive! A lot of rarer, collectible plants that aren't mass produced are less tolerant of low humidity. There are also entire plant families known for not tolerating low humidity. Calathea, Maranta, Peperomia, Stromanthe, Orchids and Ferns are some of the best-known, high humidity lovers. 


That means your more hardy indoor plants may cope fine with humidity at 50%, however even they may show signs of needing higher humidity when it gets down around 30% in typical heated conditions in winter, in air conditioned homes and apartments in summer. That doesn't mean they will suddenly up and die on you, but does mean the majority of tropical plants we keep indoors will benefit from a humidifier.


Another benefit of higher humidity is spider mites, or rather, no spider mites. These creepy crawlies in particular love hot, dry conditions. Humidity works as a great preventative, creating conditions your plants love, and spider mites hate. 


Before you get all worried and go buy the first plant humidifier you can find, look for the signs humidity is too low for your plants (below), and also check what the humidity level actually is at your place using a hygrometer (humidity meter). 


Humidity meters can be bought for as little as $10, making them a very cheap investment in monitoring your plant's environment, like these mini humidity meters. Unless you are already seeing signs that humidity is too low, get a hygrometer first (I'd get one either way, as then you'll know when you need to run your humidifier).


What are the signs a plant needs higher humidity?


The problem with low humidity is the signs look a lot like needing watering. But if you make the mistake of watering again too soon, next thing you know you're dealing with root rot, when all your plants needed was higher humidity. 


Common signs plants show of needing higher humidity are dry, 
browning leaf edges and brown leaf tips, leaves curling or cupping, and wilting leaves even when recently watered. Just like we get dry, chapped, cracked lips in air that's too dry, another sign is cracked or split leaves depending on the leaf type. 


Thinner leaves are more likely to show brown tips and edges. In thicker or rounder leaves (Watermelon Peperomia is a perfect example), cracked, split leaf edges is a more common sign. Both may curl or cup to reduce water loss through the leaves when the air is too dry. 


A common worry is how to increase the humidity of the area your plants call home, but not your entire home (unless you want to of course). That's where small-area humidifiers come in.
 

 

Which type of humidifier is best for plants?


Portable, home humidifiers fall into 4 sizes based on the area they cover. Mini, small-area, small-room and room. Mini are usually under 500ml capacity. Small-area humidifiers tend to be around 500ml to 1 litre capacity. Small-room are usually 2 litre+ capacity. However do check with the supplier on the type of humidifier and the area they cover as you can't judge it by water capacity alone. Most small and large room humidifiers will tell you the square metres.


The most popular types of humidifier for indoor plants is a small-area, cool-mist humidifier used to increase humidity just in the area your plants are in, such as covering one or two plant shelves in a corner of a room. Both a mini or small-area humidifier avoids raising humidity in the entire room or house.


Mini, cool-mist humidifiers
 are more popular for small, enclosed spaces like prop tanks and terrariums. For larger collections and small greenhouses, 
small-room, cool-mist humidifiers are a popular choice.


The type of humidifiers usually used for plants are evaporative or ultrasonic, not a diffuser, vaporiser or warm-mist humidifier. More about what each type is coming up below.


Humidifier brands and how much they cost


All sizes of humidifiers tend to be readily available in corded models, but if budget allows, cordless offer better portability to go to where your plants are, without needing to locate plants near power points, or deal with messy cords. You'll have more luck finding mini and small-area humidifiers in cordless models. Larger models tend to only come corded.

The following products and price guide is accurate as of June 2022


H2O humidifiers are a popular choice in cordless, cool-mist humidifiers for plants. They come in both mini and small-area models, from 200ml to a little over 1 litre capacity. Budget for around $40 to $80 depending on capacity and the features they come with. 


Mini humidifiers for smaller or enclosed spaces like a prop tank or small cabinet, will usually be under $30 for corded models or under $50 for cordless depending on capacity and features. The H2O brand include 2 mini-size models, a 200ml and a 400ml. 


I personally use the H2O Mini in my prop tank (a converted Exo Terra Terrarium), however my go-to for my plant shelves is the H2O 1.1 litre, which I shift to where it's needed. I also have a Crane small-room humidifier.


The next level up is small to large room, cool-mist humidifiers, with the Crane brand a popular choice. These vary from around $130 to $200. They are corded and raise the humidity for an entire room. The smaller model covers a small room up to 18.5 m2 or the larger 3.7 litre model covers up to 40 m2. A great option for a small to medium greenhouse or large collection that's mainly in one room.


I've had a Crane humidifier for years and it's still going strong. I do prefer cordless now I have my H2O humidifiers, but the Crane do have a bigger capacity and run for a lot longer than a cordless humidifier. What I'm not such a fan of is how fiddly the Crane design is to keep clean (I find them more prone to mould than the H2O), so it's not my go-to anymore, but still a great option for larger collections. They also give you more flexibility on adjusting the mist output than the H2O.

Warm mist humidifiers, also called vaporizers, are not recommended for plants. That's not to say you can't use them, just that the distance from your plants should be increased, and there's the added risk that comes from containing boiling water. 


Diffusers do increase humidity a little, however not to the same extent a purpose-built humidifier does. Whereas a humidifier won't diffuse fragrance like a diffuser does. However if you already have a diffuser, and it hasn't been used with any scents that could harm your plants, try that first (just get a hygrometer to see if it's making enough difference).

 

How close can a humidifier be to plants?


The general rule is to place a small-area, cool-mist humidifier at least one foot (about 30 cms) away from plants, walls, furniture, curtains and other electronic devices.  See below about tips for running a humidifier inside a prop tank or cabinet. Large-capacity, higher output humidifiers should be at least 6 feet away, such as ones made for one or multiple rooms. Humidifiers that boil the water to create steam should be kept further away from plants compared to cool-mist humidifiers.


You'll often see indoor plant hobbyists run a humidifier right in amongst their plants. In that situation getting a mini or small-area humidifier combined with good airflow is important. This allows placing the humidifier beside or amongst plants without causing water to form droplets on the leaves and encourage mould. It's best to use a smaller humidifier on its lowest setting when in an enclosed space.


A cool-mist humidifier is also an important consideration so leaves do not burn. Always use humidifiers on the lowest setting required to increase humidity without excess moisture causing water to condense and form droplets. 


It is highly recommended to get a hygrometer to check the current humidity level of the air by your plants and to only use a humidifier when humidity is low. Most types of heating in winter will consistently drop the humidity to levels well below what tropical indoor plants prefer, however a hygrometer is still recommended even in winter.


One concern when humidifiers are very close to plants, is water droplets condensing when the air can no longer hold the extra moisture. This can encourage mould, mildew or fungus from the high moisture without airflow, if leaves are not given a chance to dry out, or if plants can't transpire. Again, best to check humidity with a hygrometer before use. 

 

Humidifiers vs Diffusers

What does a humidifier do?


Humidifiers add moisture to the air to prevent dryness (for the benefit of people too, not just your plants). They are also used to ease cold and flu symptoms. Popular in air-conditioned and heated homes and offices.

What is a diffuser used for?


Diffusers are used to disperse scent, usually used with essential oils, to fragrance the air. Some types of diffusers, like nebulisers, are used to help alleviate health concerns like asthma. Diffusers do also release some moisture, however less than a humidifier, so may not noticeably increase humidity. Diffusers usually hold less water also. Diffusers can work in a similar way to humidifiers, but combine the oil and water into a scented mist. 

Can a humidifier be used with essential oils?


No, usually this will block or damage the motor or mist outlets of the humidifier, however there are a growing number of humidifiers coming onto the market that can be used as both. Just check first, so you don't damage your humidifier, or buy a diffuser instead.

PRO TIP: If you do get the ok to use your humidifier as a diffuser, also check that won't void the warranty. Humidifiers that can be used as diffusers tend not to work as well as diffusers (the scent won't often be as strong from a humidifier), however this will depend on how the humidifier is made.

Humidifiers vs Air Purifiers

What does an air purifier do?


As the name says, they purify or 'clean' the air. A fan sucks air in and through various filters that remove particles and contaminants - like dust, dander, smoke, bacteria and more - which then blows the 'cleaned' air out. They are used to refresh stale air.

If a HEPA filter is used, they can also reduce airborne allergens and mould. However they do not increase humidity. A humidifier does not purify or clean the air, however some humidifiers have wicks that filter out contaminants from the water source used. 

Humidifiers vs Evaporative Cooler

What does an evaporative cooler do?


A swamp cooler, or evaporative cooler, cools hot air using water. It sucks in hot air, circulates it pass water-soaked pads inside, then blows out the cooler air. The process of cooling the hot air does increase humidity, however they work best in dry, hot conditions, so are not often used in New Zealand. They also usually require a vent outdoors.

Humidifiers increase humidity, however do not cool the air. Depending on the type of humidifier, most produce moisture that is air temperature. Humidifiers can run inside without requiring an outside vent or window. Some humidifiers are a combination of both evaporative and ultrasonic, with a wick that needs to stay moist to work.

 

Humidifiers vs Vaporisers

What does a vaporiser do?


Both increase humidity, however a vaporizer - also called a warm-mist humidifier - is a type of humidifier that boils the water to produce steam, vs a cool mist humidifier that creates mist from cold or room temperature water, resulting in mist that is the same temperature (cool to room temperature).

 

What's the difference between cool-mist vs warm-mist humidifiers?


HOW THEY WORK:
 Most cool-mist humidifiers are ultrasonic, using vibrations that turn water into a cool mist. Some ultrasonic humidifiers use a disk that turns rapidly and breaks the water up into tiny particles. A steam vaporizer or warm-mist humidifier, contains a heating element that boils the water to create steam.


WHICH IS SAFER?
 Cool-mist humidifiers are recommended when used around children, pets and plants, as warm mist humidifiers boil the water, so pose a burn risk if knocked or tipped over. Warm mist humidifiers are best placed well away from surfaces or delicate leaves that may be damaged by the temperature of the mist, and in an area pets and children can't access or knock them.


WHICH IS CLEANER?
 Warm-mist humidifiers tend to be more hygienic as the water is boiled first before being turned into steam. Some cool-mist humidifiers use wicks that act as filters to reduce contaminants. This type will need the wicks replaced regularly (every 3 to 6 months on average). Although steam or warm-mist humidifiers run cleaner, using distilled or purified water in a cool-mist humidifier, regular cleaning, or using a wick humidifier all help.


Note that many humidifiers are made for use with tap or filtered water, so best to check with the retailer or manufacturer if you want to use a different water source. Using humidifiers with distilled or R/O water (water that has had the minerals removed), can reduce the mist output, however would give the benefit of keeping the humidifier cleaner longer.


MAINTENANCE:
 Another difference between cool-mist and warm-mist humidifiers is cleaning. As the water is boiled first in warm-mist humidifiers, there is less and slower build-up of mineral deposits (limescale) or mould, however just like a kettle, this can still happen over time. 

Both types still require a regular clean, however it is more important and required more often for a cool-mist humidifier. If not cleaned regularly (a quick clean once a week is recommended), limescale can build-up and block the mist outlets faster over time compared to a warm mist humidifier. Both can be cleaned with a 50/50 mix of white vinegar and water and left to air dry, or just hot water and dish soap will also do the job (just rinse well afterwards). More here about the best way to clean and maintain a cool-mist humidifier


BUDGET:
 Steam vaporisers or warm-mist humidifiers tend to be cheaper and cool-mist humidifiers tend to cost more.

 

What are the different types of humidifiers?

 

Evaporative or moisture humidifiers blow air through a moistened wick. Some models use both evaporative and ultrasonic vibration to generate mist. The mist produced varies from room temperature to slightly cooler than room temperature. The H2O humidifier brand combine both ultrasonic and evaporative, and are cool-mist, small-area humidifiers popular for plants.

Ultrasonic humidifiers generate mist by ultrasonic vibration. The Crane brand humidifiers are ultrasonic. Some ultrasonic humidifiers produce warm mist, some cool. Not all humidifiers include a filter or wick, so may be best used with purified or distilled water. 

Impeller or oscillator humidifiers rotate a disk at high speed and use a diffuser to break the water into mist.


Central humidifiers
 work as part of a home air con and heating system.


Steam humidifiers
, also called vaporisers or warm-mist humidifiers boil the water, turning it in to steam.


Some humidifiers use a fan to distribute the mist, so don't operate as quietly as humidifiers without a fan.

 

Do all types of humidifiers work with humidity controllers?


Humidity controllers like Inkbird can be used in-line with some humidifiers. They monitor the humidity and turn the humidifier on or off depending on the humidity range you set. Not all humidifiers are compatible with controllers. You'll need to check with the retailer or manufacturer that the humidifier will run when switched on, without requiring an extra step to turn them on, and that they turn off when switched off. Many need a second step before they will run, such as pressing a mist selector button. 


Most cordless humidifiers keep running even when unplugged or switched off by a controller. That's the point of being cordless after all. They don't need to be plugged in to a power source to run. Cordless humidifiers normally turn off only when the water reservoir is empty, or when the charge runs out. Some have a timer you can set for how many hours you want it to run. Most cordless humidifiers do also run when plugged in. Some only charge when plugged in but turned off. The nature of being cordless means they won't be compatible with humidity controllers. 


Can you run a humidifier inside a plant cabinet or prop tank?


Yes, you can run a humidifier in an enclosed plant tank or cabinet, such as an Ikea cabinet or Exo Terra terrarium, however you need to allow adequate airflow and choose the right model humidifier for the space, ideally one with multiple mist settings. A hygrometer is recommended, kept inside the tank or cabinet at all times, to monitor humidity and temperature.

 

5 things to watch out for before running a humidifier in an enclosed space...


AIRFLOW: Plant humidifiers do not typically have built-in fans. This means they run almost silent, but also means adequate airflow often needs to be added if used in enclosed spaces.


Best to uncover some of the top of a prop tank, or open a door on a cabinet to increase airflow when a humidifier is running. Some like the Exo Terra, have mesh tops and vents around the doors - as they are also used to house animals - so are built with better airflow in mind already.


If your prop tank is a fish tank aquarium, these are often made to seal moisture in to prevent evaporation, so airing them out while using a humidifier is extra important. Keep in mind using a humidifier in an area with low to no airflow may void the manufacturer's warranty or shorten the life of the humidifier.


BUILT-IN FAN: You can get humidifiers with built-in fans, however these often run only with the fan on, so noise may be a concern. The fan may be too strong for the plants, so a better solution could be to get a small USB fan that you can turn on and direct away from blowing directly on plants when your humidifier is running (if you can't uncover some of the top or open the door). 


SETTINGS: Whether run close to your plants, or inside an enclosed area, only run the humidifier at the minimum level the plants require, so the air can hold the moisture instead of excess condensing on leaves and shelves. Look for a model with adjustable mist or multiple mist settings


Running only when needed, and using the lower setting/s, also avoids limescale blocking the mist outlets. Droplets that form on or around the humidifier mist outlets will later evaporate, leaving minerals behind. The minerals do not evaporate, and can cause limescale. Exactly the same as your shower head or sink taps. Limescale can reduce mist output, or even block the mist outlets over time so regular cleaning is important to avoid that happening. 

OUTPUT: Adding humidity to an enclosed area, and keeping it in, is much easier than plants kept in an open space. A mini or small-area humidifier will likely be plenty. You could also look for the model with the lowest settings, even if it does have a bigger capacity, so you can turn it right down.


CORDED or CORDLESS: Cordless models are very popular for cabinets and prop tanks, however being cordless can increase the price due to the battery. Whether corded or cordless, electricity, metal and water don't mix, so check the humidifier regularly when it's running to make sure water isn't condensing on it. In very humid enclosed areas, remove the humidifier when not in use so any metal parts don't corrode over time.

 

What type of water can be used in humidifiers?


This depends on the humidifier. For many humidifiers tap water is fine to use, especially if it has a filter, however you may prefer to use distilled, purified or RO water even though most humidifiers are made for use with tap water. Boiled water or mineral water are not recommended due to the higher mineral content, which can cause limescale.  

Is tap water okay to use in a humidifier?


Some humidifier brands include a filter pad or filter wick, which makes them okay to use with tap water, as the filter helps prevent minerals from tap water ending up going through the unit or into the air.


Even if your humidifier includes a filter pad or filter wick, you still need to give it a regular clean about once a week. Check the directions for the model you get, however most filters or wicks need replacing every 3 months on average.


No matter what water you use, or what type of humidifier you get, cleaning is needed. When using tap water, cleaning helps prevent the minerals in the water causing limescale, the same white marks you'll often notice on your shower glass, around your shower head or taps. Limescale can otherwise build up over time and block the mist outlets. Exactly the same reason shower heads become blocked over time, reducing water output. 
Bacteria and mould can also build up over time if a humidifier is not cleaned regularly, like the pink or yellow slime you'll often see build-up in always-wet areas, like sink plugs. Clear humidifiers can also be prone to algae, so if your humidifier will be in a position where it gets very bright or direct light on the humidifier, consider a model without a clear water reservoir. 


Most humidifier manufacturers recommend cleaning once a week with 50/50 white vinegar and hot water. If you're worried about bacteria in tap water, a little soap and water scrub will do the trick, or you can add a little 3% food grade hydrogen peroxide in with the water each time you top your humidifier up, which kills bacteria and fungus spores.

 

Is filtered water better than tap water in humidifiers?


Filtered water and tap water
 are much the same as far as a humidifier is concerned. Unless the water is purified, not just filtered, the same minerals that cause limescale will still be present, filtered or not, as most filters do not remove minerals like calcium that cause limescale.


However tap water may include more bacteria. Especially if water is left sitting in a humidifier, which you shouldn't do anyway no matter what the water source. Always fill up with fresh water each time, and always store any humidifier dry. The same as tap water left sitting out on the bench, bacteria may multiply over time. Not something you ideally want to drink, or put in your humidifier. 


Tap water tends to produce more mist than using distilled water, so although distilled or purified water reduces limescale, your humidifier may also produce less mist than using tap water or filtered water.


Is mineral or bottled water okay to use in humidifiers?


No, it's best to avoid mineral water in humidifiers as it often has higher levels of minerals than tap water, so is more likely to cause limescale, which could block or damage the humidifier.

 

Is boiled water okay to use in humidifiers?


No, it's best to avoid putting boiled water in humidifiers. This is because boiling will help kill bacteria or mould spores, however will not decrease the mineral content. In fact, boiled water often leaves behind a higher concentration of minerals as the water evaporates but minerals do not.


Distilled water is not the same as boiling water, although both are made by heating water. Distilled water collects the steam vapor and condenses it back to water, without the minerals. Boiled water is water that's been heated then cooled.
 


What temperature water should be added into a humidifier? 


Cool to room temperature water is best for filling a humidifier. Avoid putting ice cold, warm or hot water into a humidifier. Warm water is more likely to encourage the growth of mould,. Hot water may damage the internal components. 


Another reason not to use water from the hot tap, is hot water usually contains more minerals than room temperature or cold water from the same tap, because as the hot water flows through your pipes, it will pick up minerals and build-up from the inside of your pipes, as minerals dissolve more easily in hot water than cold.

 

Where can I buy a plant humidifier in NZ?


From me here at Love That Leaf. I don't sell all the brands mentioned in this guide, however I do have the popular H2O cordless plant humidifiers which offer both mini and small-area models. I do hope to bring you small and large room humidifiers soon too (work in progress).

 

There you have it! The answers to every plant humidifier question. If I've missed anything please do get in touch and let me know. I'll answer it for you, and also add it to this guide to help everyone else - Anna :)