Troubleshooting
Crown of Thorns problems — and how to fix them
Crown of Thorns (Euphorbia milii) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Root and stem rot
The most common cause of decline. Triggered by overwatering or poorly draining soil, especially in winter. Let soil dry between waterings and always use a pot with drainage.
Few or no flowers
Almost always insufficient light. Move to the sunniest window or supplement with a grow light; the plant needs several hours of direct sun to bloom well.
Leaf drop
Some leaf loss is normal in winter or after a move. Sudden heavy drop usually signals overwatering, cold draughts, or a sharp change in light or temperature.
Mealybugs, scale and spider mites
Sap-sucking pests can nestle among the spines and leaf nodes. Inspect regularly and treat with insecticidal soap or by dabbing pests with isopropyl alcohol.
Irritant sap on cuts and pruning
Broken stems ooze a milky latex that irritates skin and eyes. Always wear gloves and eye protection, and keep the sap away from pets, children and your face.
Botrytis and leaf-spot fungus
Cool, damp, stagnant conditions invite grey mould and leaf/stem spotting. Improve airflow, avoid wetting the foliage, and remove affected growth promptly.
Prevent crown of thorns problems before they start
Most crown of thorns issues are care-mismatch, not bad luck. Dial in the basics:
Crown of Thorns problems — FAQ
Why is my crown of thorns root and stem rot?
The most common cause of decline. Triggered by overwatering or poorly draining soil, especially in winter. Let soil dry between waterings and always use a pot with drainage.
Why is my crown of thorns few or no flowers?
Almost always insufficient light. Move to the sunniest window or supplement with a grow light; the plant needs several hours of direct sun to bloom well.
Why is my crown of thorns leaf drop?
Some leaf loss is normal in winter or after a move. Sudden heavy drop usually signals overwatering, cold draughts, or a sharp change in light or temperature.
Why is my crown of thorns mealybugs, scale and spider mites?
Sap-sucking pests can nestle among the spines and leaf nodes. Inspect regularly and treat with insecticidal soap or by dabbing pests with isopropyl alcohol.
Why is my crown of thorns irritant sap on cuts and pruning?
Broken stems ooze a milky latex that irritates skin and eyes. Always wear gloves and eye protection, and keep the sap away from pets, children and your face.
Why is my crown of thorns botrytis and leaf-spot fungus?
Cool, damp, stagnant conditions invite grey mould and leaf/stem spotting. Improve airflow, avoid wetting the foliage, and remove affected growth promptly.