While the presence in wells of plants alone do not typically cause harmful health effects, their presence does indicate that the well is not properly sealed or has some other faults. If plants are present in the well, they could provide a living environment for other organic foreign objects such as rodents, insects and bacteria. In the examples below you can see where plants have shown poor construction or maintenance of the well.

https://www.youtube.com/watch?v=Gaxo3uMII_A

In the above video you can see plant roots growing in an abandoned well. The roots appear to be growing through holes in the metal casing. These holes may also allow other contaminates to enter the well and the local groundwater system

https://www.youtube.com/watch?v=JrHoyR6DP8M

The above video shows a growth on the steel casing of a well, which could be a fungus or other organic growth.