Saving a Rotting Euphorbia ingens: A London Case Study

Identification and Diagnosis

This "cowboy cactus" is actually Euphorbia ingens, a succulent. The sudden, soft browning at the base is not normal corking—it's active rot, likely from the combination of UK winter cold, darkness, and possible overwatering (even monthly watering can be too much in cool, low-light conditions). The dehumidifier helps, but standard compost retains too much moisture.

Three Options—Ranked

1. Wait and watch—unlikely to harden off; rot will likely spread.
2. Inspect roots—unpot, check for healthy white roots. If roots are firm, repot in 50/50 perlite (or sand) and sterile soil in a wider, shallow pot (⅓ plant height). Stake securely.
3. Propagate from healthy arms—recommended. Cut arms, let callous 2+ weeks, root in sterile mix.

Propagation Protocol (Followed Successfully)

1. Sterilize knife between every cut.
2. Cut 2–3 inches above rot; continue cutting until vascular tissue is clean.
3. Dust with rooting powder (no pre-wetting needed).
4. Callous 2+ weeks in warm, indirect light.
5. Root in ⅓ peat/coir, ⅓ perlite, ⅓ coarse sand—barely moist.
6. Stake cuttings; mist occasionally; no water until roots form (months).

Critical Notes

• Discard all old soil—don't compost.
• Sterilize pot with bleach.
• Rooting large bases is difficult; rest on soil and stake as alternative.
• Spring is ideal, but spreading rot demands immediate action.
• Move cuttings to a warm area during rooting.

The owner successfully amputated, found healthy tissue 2 inches above rot, applied rooting powder, and is callousing the main stem—excellent work. One arm was set aside as insurance. The white latex confirmed Euphorbia identity. Soil was discarded, pot sterilized.