[zaarn]

By experience; when a plant looks unwell, it's probably already dead and you have been watering a corpse. It's always the goddamn roots.

[Xylakant]

A common cause of death for quite a few kinds of plants is drowning. (or rather "too much water and the roots rotted away")

[namaemuta]

I'm terrible at taking care of plants but the last one I got was growing leafs until the last leaf stalk was completely dry.