How to Choose a Humidifier for Tropical Houseplants

What Humidity Tropical Houseplants Need

The best humidifier for tropical houseplants is one that can hold the room at 40 to 50 percent relative humidity and that you will clean every third day. For most homes that means an evaporative model if you fill it from the tap, or an ultrasonic model if you are willing to buy distilled water. Type and upkeep matter more than brand, because every type will raise humidity and the differences are in what else it puts into the air.

The target comes from two sources that happen to meet at the same number. Iowa State University Extension says many houseplants prefer a relative humidity of 40 to 50 percent. The US Environmental Protection Agency advises against humidifying a home above 50 percent, because higher levels may encourage the growth of biological organisms indoors. Aim for the top of the plant range and you stay inside the household limit.

Winter is when the gap opens up. Iowa State says the humidity in many homes during the winter months may be only 10 to 20 percent, University of Georgia Extension calls 10 to 20 percent typical of most homes, and Penn State Extension notes that indoor levels can easily fall below 30 percent during the heating season. Georgia’s bulletin classes anything under 20 percent as low for interior plants and 40 to 50 percent as medium, and it points out that a greenhouse runs at 50 percent or higher. A newly bought plant moved from that air into a dry living room can lose water rapidly through its leaves. If the leaves are already discolored, work through the watering and light checks in our guide to yellow houseplant leaves before putting it down to the air. For comparison, the engineering society ASHRAE recommends keeping indoor air between 30 and 60 percent.

Why a Humidifier Beats Misting and Pebble Trays

Extension services are blunt about the low-cost alternatives. Penn State notes that after a plant is misted the rise in humidity lasts only until the water evaporates, which can happen in a matter of minutes, so even daily misting does nothing for the level around a plant. Georgia’s bulletin says you would have to mist every few minutes, indefinitely, to make a difference. It adds that plants with hairy leaves should not be sprayed at all.

Pebble trays get a mixed review. Iowa State and Georgia still list them, while Penn State reports that the evaporated water diffuses into the whole room and makes almost no overall impact on relative humidity. Grouping plants close together is the one free step most sources still consider worthwhile, since the pots and leaves share the moisture they give off.

A humidifier is different because it adds enough water to change the air in the room. Iowa State calls humidifiers an excellent way to raise indoor humidity. If your furnace has a whole-house humidifier, Penn State’s view is that it helps but will not bring the air up to ideal levels for houseplants, so a portable unit in the plant room is still worth having.

Humidifier Types Compared

The EPA describes four ways a home humidifier puts water into the air, and they differ in what comes out with the moisture. The table uses the agency’s descriptions.

Type	How it works	Minerals and microorganisms sent into the air	Notes for a plant room
Ultrasonic	Ultrasonic sound vibrations create a cool mist	Can disperse both from the tank	Needs distilled water and strict cleaning
Impeller	A high-speed rotating disk creates a cool mist	Can disperse both from the tank	Same care as ultrasonic
Evaporative	A fan blows air through a moistened absorbent material	Generally less, if any	Moisture leaves as invisible vapor
Steam vaporizer	An electric element or electrodes heat water into steam	Generally less, if any	Burn risk from steam and boiling water

A warm mist humidifier is a steam vaporizer in which the steam is cooled before it leaves the machine. Evaporative and steam units can still grow microorganisms if water stands in the tank, so no type removes the need for cleaning.

The white dust that settles on leaves and shelves near some humidifiers is the mineral content of tap water, carried out with the mist. It is a problem of ultrasonic and impeller units filled from the tap. The EPA’s advice is to use bottled water labeled distilled, which holds less mineral than most tap water, and to fit a demineralization cartridge or filter if the manufacturer supplies or recommends one.

Which Type Fits Your Room

Start with your water and your household, then look at size. With hard tap water and no wish to carry distilled water home, an evaporative unit avoids the dust problem at the source. If you want a visible cool mist, choose ultrasonic and commit to distilled water and cleaning every third day. A steam vaporizer or warm mist unit is an option only where children cannot reach it, because the EPA warns that steam and boiling water may cause burns.

Size follows the space. The EPA separates portable humidifiers, which are small and easily moved, from console humidifiers, which sit in a cabinet designed for floor use. A portable unit suits a shelf or a corner of grouped plants. A console earns its floor space when a whole room has been given over to the collection. Manufacturers rate each model for a room area, and that printed rating is the number to compare against your own room, since no extension source gives a rule for square feet per plant.

When plants are spread through the house, gather the tropical ones into a single room and humidify that room. You get the benefit of grouping, and you avoid raising humidity in rooms that do not need it.

Features Worth Paying For

A humidistat is the feature that matters most for plants. It switches the unit off at a set humidity, which lets you hold the 40 to 50 percent range and stop at the EPA’s 50 percent ceiling without watching the machine. If the unit has no humidistat, or you doubt its reading, buy a separate hygrometer. The EPA notes that hygrometers are sold at hardware stores, and one placed among the plants tells you what the leaves are getting.

After that, look at how the tank comes apart. The EPA routine calls for wiping all surfaces dry every day, so a wide opening that takes a hand and a cloth is worth more than extra capacity. A tank large enough to run through the night is convenient, but you will be emptying it daily in any case.

Cleaning and Placement

The EPA sets out a routine for portable humidifiers, and it is stricter than most owners expect:

1. Every day, empty the tank, wipe all surfaces dry and refill with fresh water.
2. Every third day, clean the unit. Follow the manufacturer’s directions where they exist. Where they do not, the EPA suggests a 3 percent solution of hydrogen peroxide on all surfaces that touch water.
3. After using any cleaning product, rinse the tank with several changes of tap water so the chemical is not sent into the air.
4. Before storing the humidifier, make sure every part is dry.

Placement is a matter of watching for condensation. If water condenses on windows, walls or pictures, the EPA says to move the humidifier, lower the humidistat setting or run it less. Wet glass in a plant room is the sign that the air has passed the useful range. Dry air is not the only winter shortfall either, and a plant shelf far from a window may also need one of the grow lights for low-light apartments.

Mistakes That Cost Plants

The most common error is buying on tank size and ignoring the water. An ultrasonic unit run on hard tap water sends that mineral out as white dust on nearby leaves and shelves, and the fix is a jug of distilled water. The second is running without a humidity reading. A room can sit at 20 percent with the humidifier on low, or drift past 50 percent with it on high, and without a hygrometer you cannot tell which.

The third is letting the cleaning slide past the third day. Ultrasonic and impeller units send whatever grows in the tank into the room along with the mist. If a third-day cleaning is more than you will keep up, choose an evaporative model and a smaller collection of high-humidity plants over a large ultrasonic unit that goes uncleaned. Our list of low-maintenance houseplants for beginners is a place to start if you would sooner pick plants that ask less of you.