Ask Mr. Smarty Plants

This is an excellent question but is too broad for us to provide a very helpful, exact answer other than "ohhh, overwatering can kill your plant". I will respond by giving you a few things for you to think about so perhaps you can answer the question yourself.

When you give a plant too much water it either sits in it or it runs away, depending on the type of soil in which it is planted. Clay soil can hold moisture and drains slowly; sandy soil drains very quickly. A container plant has the same issues depending on the potting medium and the pot drainage. Excess water can drain out of pots sitting on saucers or on the ground, but if a standard pot is sitting inside a decorative outer pot, the soil will become saturated with overwatering.

How would that affect soil fertility?  What makes soil fertile?  Do you know what water soluble fertilizer is?  What if you are growing plants in "potting soil", applying fertilizer and then overwatering so that the water just runs out of the bottom of the pot?  What do you think would happen? And if the pot has no drainage, what happens to the pore space in the soil?  Do you think the plant roots can extract the oxygen they require for respiration from water?

So, do you think the plant will be happy and healthy under those conditions?   And is a stressed plant more or less susceptible to attack by pests and diseases than a healthy one?

I think you can figure out the answer to that question and can put it in your own words!