Hot in Here: Humidity 101

If you’ve ever experienced a New York summer, you might describe it as humid. The blankety, moisture-filled air that makes morning commutes sticky, skin glisten and wreaks havoc on our hair is essential for certain plants.

Hot in Here: Humidity 101

Words by The Sill

Plants 101 Next Article
If you’ve ever experienced a New York summer, you might describe it as humid. The blankety, moisture-filled air that makes morning commutes sticky, skin glisten and wreaks havoc on our hair is essential for certain plants.
Hot in Here

Humidity is a measurement of water vapor dissolved in the air. There are two kinds of humidity, 1. Absolute and 2. Relative. Absolute Humidity is defined as the literal mass of water vapor divided by the volume of the air/water vapor mixture, i.e., how much water is literally dissolved in the air.

How Humidity Works

Air is a gas, and gasses are affected by other factors like temperature and pressure. That’s where Relative Humidity comes in on the scene, defined as a percentage that measures how much water vapor is in the air, versus how much total water vapor the air can hold. This takes into account temperature and pressure. 50% humidity means that for a given temperature and pressure, the air is half-saturated with water vapor. Most humidity readings that you will come across, like in your Weather App, are the measure of Relative Humidity.

As temperature increases, the capacity of the air to hold water vapor increases. Likewise, as temperatures fall, the water-holding capacity of the air decreases. This explains why in winter it is so dry outside. Cold air can’t hold much water, and when that air is heated in our homes, the capacity increases, but the amount of water stays the same, decreasing humidity. For example, if the humidity on a cold day outside at 32F is 10%, when that air is heated indoors to 72F, the humidity drops to ~2.7%. That’s enough to irritate your sinuses and more importantly, enough to damage sensitive plants that need humidity. This can be especially bad for plants like epiphytes (orchids, air plants, some ferns) and calatheas, for whom humidity is essential.

Humidity & Plants

Plants rely on evaporation from the sun and heat to pull water throughout their plant bodies. Water can move laterally through a plant, using potassium salts, but the pulling of water, what we call transpiration (or, interchangeably, evaporation) works like this: when the sun hits the leaves, water evaporates, cooling the leaves and pulling more water to the leaves from the stem, pulling the water to the roots which are pulling water from the ground. Water travels through the plant like a straw and is able to pull itself due to the cohesive/adhesive nature of water, or because it sticks to itself and what surrounds it.

Often, humidity-sensitive plants have lots of pores and thin leaves and parts of themselves that are only a few cells thick. Because of their thinness, these parts of the plant have poor vasculature and water cannot be efficiently transported to the cells before the water leaves the plant for the air. Thin tissues give ample opportunity for water to escape to the air, making them at high risk of crisping and dying if the humidity drops. When humidity falls, the capacity for the air to hold water increases as does transpiration and water is taken from the leaves faster than water can be replaced, causing crispy leaves, especially on the edges.

Spritz & Balances 

Now that we’ve established that humidity is the measure of water in the air, the only way to increase humidity is to put more water into the air. How? Two ways. 1. Boil water into steam, leaving a large pot of boiling water on the stove for a few hours, adding water as it gets low. 2. Supersonic vibrate water into vapor, which is just a fancy way of suggesting to invest in a humidifier. A humidifier is the best way to increase humidity levels.

Spritzing only increases humidity somewhat locally for a few minutes, but when it evaporates, the humidity goes back to what it was. Spritzing can help some plants like epiphytes and ferns. That’s because these plants have the ability to absorb water through their leaves, and directly benefit from water spritzes. Spritzing other plants that do not take it well can run them at risk for foliar infection, as bacteria and fungi activate with water on leaves and can infect them when wet.

Happy, healthy, humid environments will keep your plants happy and healthy too. For the rest of us, we’ll just have to ride out the heatwaves.

Creating an Herb Garden at Home

Tired of the frequent trips to your local grocery store for fresh herbs? Here’s some tips on bringing the outside in and creating an herb garden ri...

How To Repot an Orchid

While the average tropical houseplant should be repotted about once a year in fresh potting mix, Phalaenopsis orchids are a whole different repotti...

How To Make Your Orchid Rebloom

Just as we start feeling the winter blues, our orchids start going into dormancy. When spring rolls around again, your Phalaenopsis orchid might ne...

Anthurium

Learn how to care for an Anthurium. Anthuriums are flowering plants native to the Americas. They are known for their brightly colored flowers, wh...

Phalaenopsis Orchid

Orchids are epiphytic in their native habitat, growing on trees and rock formations, instead of directly in the ground. The orchid family (Orchidac...

Aluminum Pilea

Learn how to care for the Aluminum Pilea. The small, but fast growing Pilea cadieri originates from rainforests in Vietnam. One of over 200 specie...

Maranta

Learn how to care for most varieties of Maranta. Maranta is the type-genus of Marantaceae, and is named in honor of Bartolomeo Maranta, an Italian ...

Calathea

Learn how to care for most varieties of Calathea! Calathea is a genus of neotropical rhizomatous herbaceous perennial plants; members of which are ...

Fiddle Leaf Fig

Learn how to care for most varieties of Fiddle Leaf Fig! Ficus lyrata is a species of evergreen tropical tree native to the tropical lowlands of we...

Rubber Tree

Learn how to care for most varieties of Rubber Tree! Ficus elastica is a species of evergreen tropical tree native to southern China, Southeast Asi...

Parlor Palm

Learn how to care for the Parlor Palm! Chamaedorea elegans, also known as the Neanthe Bella Parlor Palm, is one of our favorite true palms. Parlor ...

Monstera

Learn how to care for most varieties of Monstera! Monstera are species of evergreen tropical vines/shrubs that are native to Central America. Monst...

Dino Plant

Learn how to care for most varieties of Dino Plant! The Dino Plant, also known as the Selaginella lepidophylla, is an ancient rosette-forming herb ...

Norfolk Island Pine

Learn how to care for most varieties of Norfolk Island Pine! The Norfolk Island Pine hails from Norfolk Island, a small island in the Pacific Ocean...

Oxalis

Learn how to care for most varieties of Oxalis! Oxalis is the largest genus in the family Oxalidaceae and represents about 800 of the 900 species w...

Golden Pothos

Learn how to care for the Golden Pothos! The Golden Pothos, or the Epipremnum aureum, is native to Southeast Asia. It has the reputation of being o...

Pencil Plant (Euphorbia)

Learn how to care for the Pencil Plant! The Pencil Plant or Euphorbia Tirucalli is a succulent native to South and East Africa. The plant’s namesak...

Moon Valley Pilea (Pilea Mollis)

Learn how to care for the Moon Valley Pilea! The Moon Valley Pilea or Pilea Mollis is native to Central and South America. Its common name, Moon Va...

Majesty Palm (Ravenea Rivularis)

Learn how to care for the Majesty Palm! The Majesty Palm is a robust, tropical palm with graceful, feathery fronds that originates from Madagascar....

ZZ Plant

Learn how to care for the ZZ Plant! The Zamioculcas zamiifolia – or ZZ plant — is a tropical perennial native to Eastern Africa that has become pop...

Ripple Peperomia

Learn how to care for the Ripple Peperomia! The Peperomia genus has over 1000 species, but only a dozen or so make for good houseplants. The Pepero...

Philodendron ‘Silver’

Learn how to care for the Philodendron ‘Silver’! The Philodendron ’Silver’ is native to South America and has the reputation of being one of the ea...

Jade Plant

Learn how to care for a Jade Plant! The Crassula ovata (or Jade Plant) originates from South Africa. The word crassus in Latin means “thick”. The n...

Haworthia

Learn how to care for the Haworthia! The Haworthia is a miniature succulent native to South Africa, and is one of the easiest houseplants to care f...

Philodendron

Learn how to care for the Heartleaf Philodendron! The Heartleaf Philodendron (Philodendron hederaceum) is an evergreen perennial vine, native to Tr...

Bird’s Nest Fern

Learn how to care for the Bird’s Nest Fern! Native to tropical regions such as southeast Asia, Australia, east Africa and Hawaii to name a few, Bir...

Canela Tree

Learn how to care for the Canela Tree, AKA the Cinnamon Plant! The Canela Tree, also known as the cinnamon plant, is related to the culinary cinnam...

Rex Begonia

Learn how to care for the Rex Begonia! Rex Begonias are admired for their fabulous foliage. The cultivar offers a wide range of colors, textures, a...

Peperomia Plants

Learn how to care for most varieties of Peperomia! The Peperomia genus has over 1,000 species, but only a dozen or so are suitable as houseplants. ...

Peperomia Obtusifolia (Baby Rubber Plant)

Learn how to care for the Peperomia Green (or Baby Rubber Plant)! The Peperomia Obtusifolia is a succulent-like variety of Peperomia, originally fo...

Arrowhead Plant

Learn how to care for the Arrowhead Plant! The Arrowhead (Syngonium podophyllum) is native to the tropical rain forests in Central and South Americ...

From A to ZZ Plant

A common houseplant that’s easy to grow sounds like the perfect plant, right? The ZZ Plant may very well be the perfect plant, known for its adapti...

Between Two Ferns

Ferns are fabulous. They are amongst the first plants on earth to form a vascular system, allowing them to tower over mosses and grow to heights ne...

What’s My Name: Plant Nomenclature

A rose by any other name would smell as sweet. Shakespeare knew names were important. They can tell us a lot of information about something, or som...

Introduction to Bulbs

Not the electric kind you twist, but the ones you bury into soft, warm soil, lovingly water, and check in on (maybe a little too often), in hopes a...

Pick A Peperomia

Resembling the fan-favorite rubber plant, just tinier, Peperomia are plants in the peppercorn family, Piperaceae. Peperomia make great houseplants,...

Our Top Low-Maintance Houseplants for Under $20

Not only can indoor plants transform a room’s aesthetic, but they also have the ability to boost mood, increase creativity, lessen stress, and filt...

Word On The Bird of Paradise

Unusual, gorgeous, tropical. If you’ve ever mistaken a plant for a bird, or vice versa, you may have encountered a Bird of Paradise plant. Let’s ta...

C is for Calathea

Calathea (Calathea spp. and hybrids.) is a genus of neotropical rhizomatous herbaceous perennial plants; members of which are referred to generally...

Pilea peperomioides

Sure, money doesn’t grow on trees, but the Coin Plant / Chinese Money Plant (Pilea peperomioides) is worth spending some time on.

A is for Aroids

Take a closer look at this amazing yet common houseplant.

Fiddle Me This: Caring for a Fiddle Leaf Fig

Fickle, froufrou, fancy. The trendiest plant in the game is of course, the Fiddle Leaf Fig. Flip through any home decor mag or scroll down design-y...

What To Do When You See Mushrooms and Fungi in Soil

For millions of years, plants have been BFF’s with microbes found in soil, forming strong, intricate relationships. Plants interact with both bacte...

How to Learn Which Plants Are Compatible Together (AKA Allelopathy)

Plants lead inner lives that are full of #drama. In short, some plants do not get along with other plants. This is called allelopathy and instead o...

The Hole Truth: Monsteras

Big or small, prickly or smooth, a plant’s characteristics makes them beautiful and unique. They way they look can tell us a lot about them. Here, ...

How-To: Pick a Planter for Your Plant

Say perfect plant planter three times fast. Choosing a planter is not nearly as hard, once you know what to look for. Hint: read on to find out how...

Inside, Out: How-To Bring Indoor Plants Outdoors

Transitioning your indoor plants to the outdoors is not easy. Outdoor plants require extra attention and commitment—much more so than indoor plants...

Plants 101: Succulents

In The Sill's plant beginners series, we introduce some of our favorite plant types like succulents, explore where they come from, and share how to...

Plants 101: Epiphytes and Air Plants

The Sill seeks to educate and inspire all plant lovers. In our plant novice series, Plants 101, we introduce some of our favorite plant types, expl...