Title. It’s just funny to me how cautious I am not to overwater my plants when in soil. But if I cut a piece of a plant and stick it in 100% water it thrives. Wouldn’t the roots being literally underwater be “overwatered” as well?
In: Biology
I’m no biologist/botanist. Plants need water and a lot of water. But when you over water a plant bacteria fungi in the soil also grow. Rotting happens when things decay and things decay when bacteria eats at it.
Also roots need oxygen from water. When we put the plant underwater we often change the water to prevent algae buildup but also replenishes the oxygen in the water as well.
Overwatering refers to how often you water, not how much water you use when you do water.
In general, each time you water a plant you want to completely soak its root system. How often you water depends on the plant – some plants need their soil to completely dry out before watering again, others might only need the top 10% of the soil to dry before watering again.
Plants have something called Totipotency. Any plant cell has the genetic information to make any plant cell.
So to propagate a plant you usually cut its stem and put it in water as you say.
This does two things – one it stops the cutting dying – it just lost its roots and can’t drink very well! So this makes it easy.
The water also tells the bottom of the stem its good to grow roots.
Because its just water its a zero oxygen environment – this prevents root rot, because the bacteria and fungi and viruses that cause rot need some oxygen.
Overwatering soil creates a _low_ oxygen environment. That’s perfect for rot. The plant is probably in a more advanced stage and over watering can leach the soil of nutrients.
If you get water and add nutrients and grow in that instead of soil – thats hydroponics
Tl;dr – things don’t rot when in water, they rot when they are wet.
I’m going to paraphrase one of the best explanations I’ve seen on this subreddit from [this](https://www.reddit.com/r/explainlikeimfive/s/RtYhtGtnUh) thread that asked the same thing:
Basically, overwatering isn’t about how much you water, its about how *frequently* you water. This is why even after heavy thunderstorms and floods plants can survive despite literally being inundated as long as they can thoroughly dry afterwards. When you water too *often* though, the soil always stays damp and bacteria and fungi start to set in (because they thrive in humid conditions) and grow around the roots of plants, suffocating and ultimately killing them. Plants grown hydroponically don’t have this issue because very few pathogens can survive in just water.
Plant cells need oxygen to survive.
Regular soil is a relatively high oxygen environment. Pores and air spaces between the soil grains allow oxygen to enter the soil and reach the roots in the quantities that plant cells need.
Pure water is also a relatively high oxygen environment. A glass of water absorbs water from the atmosphere, and that dissolved oxygen can circulate freely to the roots or stem of the plant. This allows the plant cells to live.
Overwatered, muddy soil is often low in oxygen or lacks it entirely. Why? Because water fills the air gaps between the soil particles, preventing oxygen rich air from reaching the roots. But the water itself can’t circulate because all the soil particles block its movement (water is more viscous than air and can’t move as easily through small passages). At the same time, all the various microbes and fungi growing in the wet soil use up oxygen in the water, so none has a chance to get down to the roots anyway. The plant cells in the roots suffocate and die, killing the plant.
In short, it’s not about water, it’s about oxygen. Soil provides oxygen, water provides dissolved oxygen, soggy soil provides no oxygen.
Oxygen is pumped into the water in a hydroponic system so that the roots can get the oxygen needed. If you just sat the roots in water without doing this the plant would die.
It turns out plants need oxygen too!
… of which there is quite a lot dissolved into most water – which is why you can root cuttings in water alone.
So why does over watering cause problems in potted plants with soil?
If there is standing water in those conditions, bacteria and other microorganisms will consume all the oxygen in the standing water, in the process of breaking down organic matter in the soil – and as a result, the roots of the plant will suffocate and rot.
Overwatering compacts the soil and makes it hard for air to reach the roots, which makes it harder for the plant to take in nutrients. Imagine if you were trying to eat a nice lunch and someone kept trying to shove a pillow in your mouth.
Wait till I blow your mind by telling you this is the 2nd winter I’ve had the same green onion plant growing on my balcony in a water bottle full of water, and it grew a new sprout last week when it started warming up enough for the water to thaw.
As long as the roots have oxygen, they will survive. This is how roots can grow in water, because the water is in contact with the air to exchange oxygen. The issue is when the soil is made of of things that can rot. Most “potting soil” that is sold at the store is ground up trees, which will rot when continuously wet. When the wood chips in the “potting soil” rot, they use all the oxygen, and the roots around it die. If there is nothing in the soil that can rot, then there is no such thing as overwatering. If your plants live in a well drained sand/silt/clay mixture, you can water as much as you want and the plant will never ever rot. Water has oxygen in it when it rains or we water, so there has to be something in the soil to use up that oxygen to kill the roots. Growing a plant hydroponically (roots in pure water) is the fastest way to grow a plant because the roots have unlimited water and oxygen. The most lush place on Earth is the rainforest, where it rains everyday, and the soil never dries out, yet the plants seem to do OK there (because the roots are in soil made of minerals that don’t rot, and the leaf litter, mulch, compost etc is all sitting on top of the soil where it can rot into compost with access to oxygen). This whole “wait until your plant is dry before you water it or you’ll kill” thing is only because they sell potting soil that is full of things ready to rot if they stay wet too long. If your soil is made of minerals (dirt) and therefore can’t rot, there is no such thing as overwatering and you’ll have happy plants.
Here are a couple videos that explain this:
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