why does overwatering a plant kil it?

Answer 1

There are several reasons why overwatering kills a plant. The other responses are correct that oxygen is needed by the roots to remain alive, although they will survive for some time on reduced oxygen. Long term overwatering for many plants will cause such a problem but plants like rice do well flooded of course. The combination of low oxygen and the potential for attack by soil microbes (bacteria and fungi) is usually the cause of plant death. An oxygen starved root is easy pray for microbes, thus the dual problems result in most plant loss.

Answer 2

Unless it is a water plant, you are drowning it! Most plant's will have a tag on the side telling you how often to water, what kind of light ( full sun or indirect sun) You are over loving it.
They do have plant's that grow in just water alone.
I am sure you can find your answer on the internet somewhere's.

Answer 3

the roots of plants take in o2 for respiration from the air present in the soil. due to overwatering, this air is replaced by water. hence, plants die due to the stoppage of respiration in the roots.

Answer 4

They are unable to take nutrients from the soil because their cells are too engorged with water.

Answer 5

Think of it as drowning; you can drown, so can a plant.