Should You Mist Your Plants? Myth Busted?


Misting has been a hotly contested topic in the gardening world. It’s a case where you’re on the extremes of the arguments – it’s either you think that it’s a waste of time or the secret technique in raising a healthy plant.

Misting with mist sprayers has no beneficial effect on the plant since it cannot raise the relative humidity for an appreciable period of time. Misting with humidifiers is a more sensible solution since it guarantees a constant and even level of relative humidity conducive to plant growth.

Let’s settle the debate once and for all by looking at the facts. Is it really one-sided or is there more nuance in the misting controversy?

So What’s the Point of Misting?

The supposed purpose of misting (especially manual misting) is to raise the relative humidity for indoor plants by directly spraying the plant leaves and stems with water. It is contested to be beneficial for indoor growing environments which have poor relative humidity, especially in certain geographic climates (either extremely arid or extremely cold).

Misting is said to be more effective on tropical plants since the tropical climates where these plants are endemic have naturally high humidity. Many popular houseplants such as the Birds of Paradise, the Dragon Tree, the fiddle, among others have tropical origins.

Others propose that it’s for the sake of providing the plant leaves and stems with the necessary moisture, hydration that they need. In addition, it is stated that it has the added benefit of spraying away the odd bug here and there or wiping away dust accumulation.

The Science of Plant Anatomy

To best understand the reason behind the theory of misting, we first have to understand basic plant anatomy. Plant leaves have tiny holes (stomata/stomata) which allow them to intake nutrients, water, and gas. The stomata have an important role in gas exchange and the vital process of photosynthesis.

The ambient humidity affects the size of the stomatal opening. This is a biological mechanism built into plants to help them retain moisture. The lower the humidity, the smaller the stomatal opening. The higher the humidity, the larger the stomatal opening. Hence, there needs to be a balance in getting the right humidity conducive to plant growth and health.

Relative Humidity and How To Determine

Sources opine that the ideal humidity for plants ranges from 30-40% relative humidity depending on the plant type as different plant varieties have different preferences as well.

It’s recommended that you first measure the humidity of your area since relative humidity will vary based on geographic location, climate, and indoor conditions.

Relative humidity can be determined by using a hygrometer. Traditional hygrometers are a hassle to use because they require some patience and skill from the user. For more tech-savvy users, this Wireless Hygrometer, here on Amazon, has iOS and Android integration to keep you updated on your room’s ambient temperature and relative humidity.

The Two Methods of Misting

There are two predominant forms of misting.

The first is by misting with handheld misters (we will call “manual misting”) This can be done by simply putting water in a sprayer and pulling the trigger to mist the plant.

The second is through the use of humidifiers (we will call “humidifier misting”).

Misting Plant Infographic

Misting with Mist Sprayers

Misting done with handheld misters is pointless as it will only increase the surrounding humidity of the plant for only a few minutes. It will not raise the relative humidity to the constant desired level.

Whatever benefits they may bring are so short-term as to be unnoticeable under any circumstance. Manual misting is ultimately a futile practice.

Negative Effects of Misting with Mist Sprayers

The number one problem in misting plants is the development of pathogens. Powdery mildew is one of the most common problems due to the high humidity environment caused by misting habits. This is particularly true for herbs indoors where the excess humidity caused by misting associated with a lower ventilation (compared to outdoor) creates the best environment for pathogens, and insects to thrive.

Another problem is the open stomata. Let me explain!

Inferencing the natural world, exposure of plants to rain can cause a plant to close its stomata to prevent it from intaking excess water. This is detrimental to the growth of the plant because open stomata are necessary for photosynthesis. Closed stomata will necessarily prevent the plant from intaking carbon dioxide (CO2). The stomata would open after several hours to two weeks, depending on the plant.

Manual misting will also close the stomata of the leaves. Since the presumption is that indoor plants are regularly watered, manual misting will cause the plant to close the stomata because the plant would not want to intake excess water.

There’s also the unwanted effect that water dripping from the leaves or stems of the plant will spread insects and pathogens. The claim that manual misting can help clean up the plant from dirt and dust may be misplaced as dirt and dust would only accumulate and condense upon getting wet. This may cause the wet dirt and dust to dry and cover the stomata.

Are You Taking Care of the Plant or Yourself?

Manual misting is a scarcely beneficial act for the plant. Rather than for the benefit of the plant, the act of misting the plant puts the gardener’s mind at ease and makes him or her feel like they’re doing something more engaging.

It’s a deliberate and simple act that lets the gardener take a more active, more frequent role in the plant’s life since manual misting is recommended to be done every morning. However, even doing it every day will not provide any real tangible benefit to the plant.

Misting with Humidifiers

Humidifiers have some merit to them as they actually work as intended. Since they are running constantly in the background, they can assure that the relative humidity of a room will increase by a certain percentage, depending on the settings.

Compared to manual misting, humidifier misting is the only beneficial and worthwhile misting method. These will substantially alter the humidity of the room as long as they are kept running.

Which Humidifiers Can I Use?

You can use almost any humidifier. There are plenty of run-of-the-mill humidifiers which can do the job of raising the humidity. The mechanics of humidifiers are relatively simple whereby dry air passes through a damp filter causing the water to evaporate thereby introducing moisture in the air. It can also work by simply boiling the water into steam or by using a vibrating diaphragm to convert water into tiny droplets.

For a beginner humidifier, the Ultrasonic Humidifier, here on Amazon, presents great value while being quiet and hi-tech at the same time.

How to Use a Humidifier for Your Houseplants 💦🌱

Use of Humidifiers in Greenhouses

A constant level of humidity is necessary for plant growth and development. Large-scale humidifiers are used in greenhouses and these are more advanced as the system itself monitors the relative humidity and humidifies accordingly, making sure that it does not reach below 30%.

Precaution in Using Humidifiers

In a confined and enclosed space, too much relative humidity (50-60%) will cause mold to grow. The risk is further elevated at 80% relative humidity.

This is further exacerbated if the area is small since mold and bacteria grow easier in said areas especially if humid (i.e. bathrooms). The combination of a small workable area and a high level of humidity may be detrimental to growing plants since harmful molds may grow on their leaves, stems, or on the soil.

Other Ways To Increase Humidity

There are other ways to increase humidity to make a dry room more comfortable for your plants and for yourself.

Grow Tent

The simplest way to control the humidity is to confine the growing area of the plants. This can be done by implementing a grow tent. The smaller the confined area, the easier it is to regulate relative humidity. Placing water or a wet towel under the grow lamp is sure to increase humidity due to evaporation. A humidifier inside a grow tent will also suffice.

Add More Plants

Adding more plants in the room can help the overall humidity optimal for plant growth. Moisture in plants transpires and evaporates into the air, increasing relative humidity. That’s why areas with lots of vegetation feel humid and easy to breathe in.

Group Plants Together

Grouping plants together creates a small pocket of humidity through transpiration. By grouping the plants in a single area or within a single pot, you can assure that the transpiration of the plants work in conjunction with one another, creating a conducive humid condition for their growth.

Air-Dry Clothes In-Doors

Hitting two birds with one stone. You can finish your laundry and at the same time make your plants happy. Just dry your clothes indoors to increase the humidity by placing the still-wet, hung clothes.

Leave the Bathroom Doors Open

Though we all love our privacy, leaving the bathroom doors open can help increase the relative humidity. Bathrooms are naturally humid environments which is why you’ll see plant life adapting easily in a bathroom setting.

While taking a warm shower or bath, leave the door open to let the evaporated water diffuse from the bathroom to other areas that require more humidity. You can also not drain the used hot bathwater as these will still release evaporated water which will raise humidity.

When is Misting Necessary

If you live in states or countries with tropical climates, it is unlikely that humidity will be a concern. The only exception is if the indoor humidity is unusually high or low. However, indoors, with the lack of ventilation, misting can also be a problem as the environment can stay humid for very long.

If you live in extremely arid or cold areas, the air there cannot carry as much water vapors for obvious reasons. Dry air does not have moisture whereas cold air cannot retain as much moisture.

Mist in Foliar Fertilization and Aeroponics

Though not meant for the sake of increasing the humidity to induce plant growth, there are variations of the manual misting method.

Foliar fertilization is the use of a dilute solution mixed with fertilization, herbicides, and pesticides sprayed directly to the plant leaves. Hence, it is like manual misting but with additives that directly increase yield and plant growth. This has agricultural applications in producing plentiful produce.

Similarly, aeroponics has similar principles but in this case, the nutrient-rich mist is sprayed at set and consistent intervals directly at the suspended plant’s exposed roots. Aeroponics is a branch of hydroponics which means that it is a soilless solution. However, implementing an aeroponic system is somewhat difficult because it requires a good degree of knowledge and technical know-how to make it successful.

Takeaways

  1. Manual Misting does not have any benefit in raising the relative humidity surrounding the plant. A couple of sprays will only raise the humidity for just a few minutes.
  2. Humidifier Misting is effective and beneficial to plants for the purposes of raising the relative humidity
  3. Relative Humidity is dependent on location and climate. Before committing to humidifying an area, check the relative humidity first because you would not want to risk increasing the humidity

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Sources

“A Brief Guide to Mold, Moisture and Your Home” by the United States Environmental Protection Agency in EPA

“Design and Construction of an Inexpensive Homemade Plant Growth Chamber” by Katagiri et al in PLoS ONE 10(5)

“Effect of misting on transpiration and conductances of a greenhouse rose canopy” by Katsoulas et al in Agricultural and Forest Meteorology 106(3)

“Effects of Foliar Fertilization: a Review of Current Status and Future Perspectives” by Niu et al in Journal of Soil Science and Plant Nutrition 21 (2021)

“Foliar Fertilization of Crop Plants” by Fageria et al in Journal of Plant Nutrition 32(6) 2009

“Fungal and bacterial growth in floor dust at elevated relative humidity levels” in Dannemiller et al In Indoor Air 27(2)

“How do room humidifiers work?” by Alexandra Cheung in How It Works

“How to Find the Right Humidity Level in Your Home” by n/a in Deljo Heating

“Humidity-loving houseplants need a little mist. Here’s how to give it to them” by Lisa Boone in LA Times

“Hygrometers” by Chris Woodford in Explain That Stuff

“Mold Course Chapter 2: Why and Where Mold Grows” by the United States Environmental Protection Agency in EPA

“Overview of the aeroponic agriculture -An emerging technology for global food security” by Lakhiar et al in International Journal of Agricultural and Biological Engineering 2020: 13(1)

“Relative Humidity and Mold” by Scott Wieringa in IndoorScience

“Stomatal Closure in Flooded Tomato Plants lnvolves Abscisic Acid and a Chemically Unidentified Anti-Transpirant in Xylem Sap” by Else et al in Plant Physiol (1996) 112

“Stomatal responses to changes in humidity in plants growing in the desert” by Schulze et al in Planta 1972; 108(3)

“The Effect of Temperature and Moisture on Microorganism Growth” by Erik Arfalk in The Compressed Air Blog

Andrea

A young Italian guy with a passion for growing edible herbs. After moving to the UK 6 years ago in a tiny flat, it was impossible to grow herbs outside. So I start my journey in growing indoor and so I decided to share my knowledge.

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