Mushy or Blackened Stem Base
A soft, discoloured, or collapsing stem at soil level is a more urgent version of root rot and often needs faster action to save the plant.
Common causes
Advanced root or crown rot
Prolonged waterlogging has spread from the roots up into the stem tissue. Unpot immediately, cut away all soft or discoloured tissue back to firm, white interior, and repot in fresh, dry mix — or take healthy cuttings if too little sound tissue remains.
Cold or frost damage
Exposure to near-freezing temperatures can rupture stem cells, causing a similar blackened, mushy collapse. Move sensitive plants away from cold windows and unheated rooms in winter.
Fungal stem rot
Certain soil-borne fungi (such as Pythium or Phytophthora) attack stem tissue directly, especially in poorly draining soil. Improve drainage and avoid letting water pool at the base of the plant.