A lot depends on your plant. Different plants evolved in different habitats. A plant from a tropical rainforest might do just fine. It has adaptations that protect the roots when they are in wet soil. A desert plant may die because it evolved in sandy soils that water flows right through. Its roots may rot. Of course, any plant has its limits.

Your question is interesting because a lot of people don’t think about how plants “drink.” Animals can regulate how much water they drink. Things are more complicated for plants.

How does a plant draw water up from the ground in its tiny tubes? We pump blood up from our feet because there’s pressure from out heart (a pump). There are also one-way valves that keep blood flowing back to the heart when the muscles around our veins contract. But plants don’t have hearts, so how do they move water up when gravity is pulling it down?

The answer is the sun. Leaves have tiny holes that you can’t see without a microscope. These holes allow the plant to move oxygen and carbon dioxide in and out of leaves.

They also allow water to evaporate, meaning change from a liquid into a gas (water vapor). That takes energy in the form of heat from the sun. Water molecules stick together, so when one water molecule evaporates into the air, another water molecules gets pulled up. It’s almost like a chain of water molecules going down into the ground. Plants can control how much their leaf holes are open, but they need them open sometimes to move gases in and out.

Water gets into plant cells by osmosis (os MO sis). An easy way to think about osmosis is that water follows solutes. A solute might be a salt, a sugar, a protein, or something like that. The insides of plant cells have lots of solutes, so water tends to enter the cells. There’s a limit to how much water can enter because each plant cell has a rigid wall around its cell membrane. Think of it this way, you can fill a balloon with water until it bursts, but if you put the balloon inside a box that wasn’t too big, you could only put in a limited amount of water.

Animal cells like ours have cell membranes, but no cell walls. They are also full of solutes. What do you think will happen if you put an animal cell in pure water?

It is very tempting to water your plants a lot to give them love (I am guilty of that a few times myself). Plants, just like us humans, need some basic necessity to live happily. These include water, food, and air (oxygen). For plants, their roots are the primary source that absorbs food (nutrients in the soil, also in fertilizer), water (also in the soil and you need to add extra water from time to time), and oxygen (which exists in the space between particles of the soil). So when you add too much water to your plants (also known as overwatering), your extra water would take up space where oxygen used to be. In other words, it would drown your plants :( .

Similarly, you do not want to pack up the soil too tightly either, as that would also reduce the space for the oxygen in the soil. Instead, you would shovel the soil, so that your plants can absorb nutrients, water, and oxygen better.

Growing plants well needs some skills of balancing just the right amount of food, water, and oxygen for the plants, but with some scientific knowledge, we all can do it!

Hi Maria - good question! Generally, plants do not like too much water. It’s like if you were wearing all your clothes, got totally soaked, and didn’t get to change out of them. It’d be really uncomfortable.

When plants get soggy, their roots start to rot. This is generally due to:
1) too much water and
2) not enough drainage.

It’s also a bigger issue with indoor plants, because they aren’t outside to dry out. Root rot can be caused by a few things, but generally it’s a mold in the genus Phytophthora. Fungi in that genera are pathogens, which means that they get their energy from infecting live organisms. The mold gets into the roots and starts to eat away at the tissue. As a result, the plant will die because it doesn’t have roots to get nutrients from the soil.

However, you can still save a plant that has root rot if you catch it early enough! The best indication of root rot is yellowing leaves on the plant. You can just let the soil dry out completely before watering again, or repot in fresh soil.

Hi Maria! Great question! Water is needed to transport nutrients through the plant and to maintain enough pressure in the plant so that it can stay upright (called "turgor pressure"). But, the roots of the plants also need oxygen and they get it from tiny little pockets of air that exist between soil particles. Adding too much water can fill in all those little gaps in the soil, so the roots don't have access to that oxygen. Another thing that can happen is that really wet soil can cause fungus to grow and that fungus can cause plant roots to rot.

Plant draws a massive amount of water from the soil everyday through a process called transpiration. In higher plants including pines, palms, and magnolias, the root takes up water and sends them to the xylem in the stem. A continuous water column goes all the way from the root to the leaf where the water is evaporated into the air. About 97% of water a plant takes are lost to the atmosphere and only a tiny fraction are used for photosynthesis.

That being said, too much water will replace the air pockets in the soil and subsequently suffocate the root. This prevents normal transpiration, which means that the plant cannot remove the water themselves. If the excess water is not drained, the plant will eventually die.

That depends on the plant, and why too much water is too much? If you waterlog the soil, then the roots won't get any air and the plant may drown. If you keep a plant that is used to dry environments wet all of the time, it may get attacked by fungus that can harm the health of the plant. If the soil is too well-drained, then you may wash the nutrients that the plant needs out of the soil and starve it, or at least require you to give it some fertilizer.