Skip to content

Why do Plants Need so Much Water for Healthy Growth?

Vegetables Getting Watered By Irrigation.

Our gardens get a lot of water movement from rain, hoses, and watering cans.  But why do plants need water so often, and what do they do with it?  Let’s discover the role of water in plant growth and how plants use water in so many ways.

Transpiration:  Water’s Journey From the Roots to the Leaves

Any discussion of water and plants has to start with transpiration.  This is where water flows from the root system through the entire growing plant.

Water flow relies on water evaporating through all the plant’s above-ground parts, including the flowers or fruit.  By far, most of the water evaporates through the leaves.  Studies have determined that plants lose 97% – 99% of their water through transpiration.

The amount of water evaporating from plants is so great that it affects the climate.  Nowadays, the phrase “affects the climate” always seems to make people’s heads explode.

Many beneficial things have to happen to the climate to maintain life.  The water vapor from plants is one of those things.  After all, water at the Earth’s surface has to return to the atmosphere to become rain again.

How Does Transpiration Move Water Through a Plant?

The accepted way of explaining transpiration is that water moves through a plant because of different water potentials.

  • For water to flow from the soil to the roots, the water potential in the roots must be lower than in the soil.  A simpler way to say it is the soil is moister than the roots.  With dried soil, transpiration shuts down.
  • The water from the roots flows toward the lower potentials in the stems, branches, and leaves.
  • Much of the water that ends up in the leaves will evaporate.  This gives the leaves the lowest water potential.  In this way, water absorbed at the roots continues to flow to all parts of the plant.
  • Transpiration will shut down if there’s high humidity.  Too much moisture in the air gives it a higher water potential than the leaves.  That stops evaporation from the leaves.

Most of the water evaporates through tiny pores on the leaves called stomata.  The stomata also bring carbon dioxide into the plant and release oxygen.

Plants use carbon dioxide to make food and expel oxygen as a waste gas.  Yes, plants treat oxygen as a waste gas.  This all happens through the process of photosynthesis.

The primary purpose of the stomata is to support photosynthesis.  Because of that, they’re open during the day and closed at night.  Like human sweat glands, the water evaporating from the stomata cools plants in the heat of the day.

A Look at a New Theory for Transpiration

Another theory about transpiration is in the works.  This new theory will attempt to explain how liquids move through all living things.  It involves EZ water, or “Exclusion Zone” water.

EZ water is a recently discovered fourth phase of water (besides solid, liquid, and vapor). Much evidence is coming out that EZ water could be a major mover for water in plants and blood in our bodies. We won’t get into the many interesting details here.  Instead, I recommend the book “The Fourth Phase of Water:  Beyond Solid, Liquid, and Vapor” by Gerald Pollack.

What are the Types of Transpiration?

Botanists recognize three types of transpiration:

  • Stomatal.  This transpiration is through the stomata.  By far, it serves as the most significant source of transpiration.
  • Lenticular.  These are small openings in woody stems and branches but also appear on some fruit.  Lenticels have much lower transpiration rates, and not all plants have them.
  • Cuticular.  Leaves have a waxy coating called a cuticle.  Transpiration through leaf cuticles accounts for 5 – 10% of all transpiration.  When the stomata close, most transpiration occurs through the cuticles.

Photosynthesis:  Making Food From Water and Carbon Dioxide

This process deserves the adjectives “amazing and “miraculous.”  It happens in tiny objects called chloroplasts, which contain chlorophyll.

We discussed earlier how plants absorb water and carbon dioxide.  Exposing chlorophyll to sunlight causes it to break the chemical bonds in CO2 and H2O.  This is the first step in rearranging carbon, hydrogen, and oxygen into glucose and other carbohydrates.

Chlorophyll doesn’t do this alone; other enzymes and processes must finish the job.  You could call chlorophyll the “sparkplug” that gets the engine started.

Through photosynthesis, plants produce FOOD from water and carbon dioxide.  They produce more than enough food for themselves and all life on Earth.  Photosynthesis not only creates food; its “waste” products are pure oxygen and water!

What are the Basics of Photosynthesis?

Look at the formula for photosynthesis in the image above.  The left side shows carbon dioxide and water.

What do humans get when we mix carbon dioxide and water?  Right, carbonated water!  We don’t get glucose and oxygen no matter how long we wait.  So, how do plants turn club soda into food?

The mystery lies at the arrow.  The writing shows a small part of what happens between the left and right sides.  Sunlight and chlorophyll start by breaking the bonds in water and carbon dioxide.

That all happens in the chloroplasts.  The formula doesn’t show any clues about the other necessary events.

That means this formula is a simplistic example.  Besides making glucose, other enzymes and processes work to create additional carbohydrates.  The exact ones depend on the plant.

Think of starchy vegetables like potatoes; the starch comes from photosynthesis.  How about the fructose in a ripe apple?  Yep, you got it.  The point is that photosynthesis is more complicated than a basic formula from a textbook.

Water Brings Nutrients From the Soil

Did you know water has a nickname?  Actually, it has several.  The one that scientists and engineers like to use is “the universal solvent.”

That’s because water dissolves more substances than any other liquid.  Note that it says it dissolves more substances; it doesn’t say water dissolves everything.

Healthy soil contains lots of nutrients and minerals that are important to plants.  Some of the vital minerals are compounds of potassium, calcium, magnesium, and iron.

Water can dissolve most of these mineral compounds.  Once dissolved, water acts as a carrier for them.  It also carries other nutrients that come from organic matter in the soil. 

Through transpiration, water moves these substances into the plant cells.  While water moves in the good stuff, it also removes waste matter from the plant cells.

Water Maintains Turgidity in Plant Cells

All healthy plant and animal cells have turgidity.  This is a swollen state that enables cells to maintain their structure.

I know some of you are thinking, “What about trees? They have wood to hold them up.”  That’s true for mature trees, but those trees come from seedlings.

The seedlings would have died without turgidity.  Mature trees will die without it, too, because their leaves will wilt.

Turgidity comes from water within the cells, not outside the cells.  A remarkable feature of cells is that they can allow water in and also prevent it from leaving.

That allows the water inside the cells to push against the cell walls and create turgidity.  As a result, plants maintain a firm structure.

Temperature Regulation:  Water is a Plant’s Air Conditioner

We discussed earlier that plant leaves have tiny openings called stomata.  The stomata support photosynthesis by opening during the day and closing at night.  While they’re open, they absorb carbon dioxide and discharge oxygen and water.

Like human sweat glands, the discharged water evaporates and cools the leaves.  If this didn’t happen, the inside of a leaf could get hot enough to kill it.

Water Improves Disease Resistance

We recognize that eating healthy food, drinking good water, and keeping clean are major steps to prevent disease.  The same things are true for plants.

Lack of water slows down or stops all the vital activities in plants.  That weakens the plant and makes it vulnerable to diseases and pests.  The damage could get so bad that the plant won’t recover once it gets hydrated again.

Water Transports Hormones and Enzymes

Living things make small amounts of enzymes and hormones to support their existence.  Since the quantities are small, they need something to transport them through the organism.  Whether it’s plant sap or blood serum, the main ingredient of the transporter is water.

Water Dilutes Waste

Inside the plant, lenticels and stomata discharge some of the wastes formed as plants grow.  Water carries other wastes for storage in the bark, roots, or leaves.

This internal storage of wastes turns out to be another miracle in plant design.  What the plant considers waste (like oxygen) benefits humans and other life.  Some of these wastes also protect the plant and repel pests.

Internal plant wastes start with water.  These “wastes” include resins, gums, rubbers, tannins, and essential oils.  Remember the role water played the next time you enjoy the smell of cedar or the taste of sassafras.

Rainwater is vital for diluting wastes external to plants.  Depending on the source, tap water, hard water, or softened water can deposit salts or chemicals in the soil.

Over time, these substances accumulate to levels that will harm plants.  This is especially true with potted plants.

Rainwater protects plants by diluting any accumulated salts or chemicals.  It also leaches these substances into the soil below the level of the roots.

Do you like honey?  It wouldn’t exist without water.

We all enjoy spending time outside on a warm spring day.  It gets better with a hummingbird hovering among the flowers collecting nectar.

In the past few years, I’ve paid much attention to honeybees.  I’m glad when I see more of them collecting nectar from the flowers on the vegetables and herbs.

Organs called nectaries produce that fantastic substance.  Plants that make nectar have to divert some of their water, energy, and glucose to that task.

The plants don’t give this nectar out of the goodness of their little green hearts.  They have a sneaky ulterior motive.  Anything that takes nectar also picks up pollen and spreads it to other plants.

That way, reproduction occurs to produce seeds to start the next generation.  God’s brilliant and miraculous design, once again.  And it doesn’t happen without water.

Seeds Need Water to Sprout

In the previous section, we discovered that plants use water to make nectar.  The nectar attracts pollinators that spread the pollen to create seeds.

Now, suppose we have a bunch of seeds.  If the seeds stay dry, they won’t sprout.  They’ll even die if they remain dry long enough.

Once again, we have to bring water into the picture.  Seeds need water to soften their hulls and activate enzymes that help sprouting.

In this case, water acts as a signal telling the seeds it’s time to sprout.  In nature, this happens during the warming, wet days of early spring.  That way, seeds start growing when the temperature and moisture are ideal for it.

To help you ensure your plants are getting the right amount of water, try our online Garden Water Calculator.

A Lesson About Plants and Water From the Movies

Many of you have seen or heard about the movie “Idiocracy.”  This hilarious cult classic by Mike Judge takes place around the year 2500.  After 500 years, mankind is far dumber.

A side story in this movie is that humans only use water to flush toilets.  People believe it’s disgusting to use water for drinking or watering plants.  Instead of water, they use a product called “Brawndo.”

For drinking, they advertise Brawndo as “The Thirst Mutilator.”  For plants, the popular phrase is “Brawndo, it’s got what plants crave.  It’s got electrolytes.”  So, the Idiocracy world hydrates themselves and plants with something like Gatorade.

Needless to say, agriculture in the Idiocracy world is dying out, and people don’t know what to do.  The problem is obvious.  The electrolytes (salts) in Brawndo are killing all the plants!

Luke Wilson plays the hero of this movie.  His character has two names:  Joe Bauers and Not Sure.  Don’t ask how he got the name Not Sure.

That scene is one of the funniest parts of the movie.  You’ll have to watch it because I won’t spoil it for you.

Anyhow, Joe has to convince the government that they need to stop using Brawndo and use water instead.  Using water for anything other than flushing toilets is a ridiculous idea to them.  More funny scenes ensue as Joe tries to convince them to use water.

Final Thoughts

We didn’t get into any serious chemistry in this article, and that was deliberate.  Even basic knowledge shows us that water is the ideal liquid for plants and all other living things.  Every internal process for life needs water.

When you get into more details of the physics and chemistry of water, you find that it’s a fascinating substance.  Even the fact that frozen water floats on liquid water makes it unique compared to other liquids.

No new discovery will ever replace or improve water.  All life works with a liquid made of two hydrogen atoms and one oxygen atom in a covalent bond.  Brawndo or Gatorade can’t replace water, so choose clean water for yourself and your plants!

Bob Styer

As a child, I hated gardening. That was mainly because Dad expected us to work in the garden every so often even though we thought play was more important. Over the years, though, I've developed a real appreciation for growing things. Whether you're growing plants for food or to enjoy their beauty, gardening can make your life better. Seize the moment!

Back To Top