Plant care guide
Alocasia Root Rot: Tell It From Dormancy, Then Act
Updated
Why does my Alocasia have root rot?
Alocasia root rot means wet mix plus roots that are brown to black and mushy, often with a soft base. Winter dormancy looks similar from above, because leaves die back, but a resting plant has dryish mix, firm roots and a firm corm. The RHS warns that overwatering, especially while dormant, rots the roots.
What to do first
Unpot the plant and check roots and corm before doing anything else. Trim soft, dark roots, keep only firm tissue, and repot in fresh, gritty, free-draining mix. Keep it warm and water sparingly until new growth starts.
An Alocasia losing leaves can mean two very different things. It may be resting for winter, or its roots may be rotting. From the top they look alike, and the wrong response makes things worse. The RHS warns in its Alocasia growing guide that overwatering, especially while the plant is dormant, can rot the roots. The only reliable check is underneath.
Rot or dormancy?
| What you find | Likely state | Source |
|---|---|---|
| Leaves dying back in late autumn or winter, mix fairly dry, roots and corm firm | Dormancy | RHS |
| Leaves yellowing or wilting while the mix stays wet; roots brown to black and mushy | Root rot | University of Maryland Extension |
| Base of the stems soft, dark or collapsing | Stem or crown rot | NC State, Clemson |
| Damage after a cold draught or a room below 10 °C (50 °F) | Cold damage | RHS |
| One old leaf fading while a new one opens | Normal turnover | RHS |
The RHS says Alocasias need a cooler, drier winter rest and may lose some foliage, then produce fresh leaves in spring. Our dormancy guide covers a resting plant in detail. This page is for the plant whose roots are failing.
University of Maryland Extension describes root rots of indoor plants as yellowing, browning and dieback of leaves, with roots and crown turning brown or black. Plants with Phytophthora can wilt even when the mix is moist. Clemson HGIC adds that stems may be girdled near soil level by a ring of brown or black tissue.
Why Alocasia rots
NC State lists root rot among the problems caused by overwatering Alocasia. For Alocasia × mortfontanensis, sold as ‘Polly’ or A. × amazonica, NC State adds bacterial stem rot.
Three things make it more likely:
- Watering a resting plant. The RHS says to reduce watering to a minimum in winter.
- Dense or oversized pots. The RHS suggests adding horticultural grit to the compost, and moving up only about 5 cm (2 in) in pot diameter at a time.
- Cold. The RHS advises keeping Alocasia above 10 °C (50 °F) at all times, and at least 16 °C (60 °F) in the growing season.
Clemson’s guide to houseplant diseases and disorders explains that overwatering cuts the oxygen available to roots and favors root disease.
What to do
Wear gloves. The RHS notes that Alocasia sap can irritate skin.
- Stop watering.
- Unpot the plant and gently remove the wet mix.
- Sort the tissue. Rotted roots are brown to black and soft, and the outer layer may slide off, as Maryland Extension describes. Press the corm or base. Firm tissue is worth keeping; mushy tissue is not.
- Trim the rot. If only a few roots are affected, Clemson advises cutting them out and repotting in sterile mix. Cut away any soft corm or stem tissue back to firm, clean tissue.
- Keep firm pieces. The RHS propagates Alocasia by separating offsets and dividing the fleshy rhizome. Firm offsets or corm sections can be potted on their own; our corm and pup guide explains how.
- Clean the pot or use a new one. Clemson suggests scrubbing pots and rinsing them in one part bleach to nine parts water.
- Repot in fresh, gritty mix. The RHS suggests about three parts peat-free houseplant compost to one part horticultural grit. Use a pot only slightly larger than the root ball.
- Keep it warm and bright. The RHS recommends bright but indirect light and temperatures above 16 °C (60 °F) during the growing season.
If nothing firm is left, Maryland Extension advises throwing away severely infected plants.
Watering afterwards
- In the growing season, the RHS waters once the top 5 cm (2 in) of compost has dried.
- In winter, keep watering to a minimum, as the RHS advises for a resting plant.
- Empty the saucer after watering.
- If leaves droop again, check the roots before changing anything. The RHS leaf damage guide uses brown, soft roots as the sign to cut back on water.
Leaves damaged by the rot will not recover. Remove them at the base once they fade, as the RHS advises. Judge progress by firm new roots and a new leaf from the centre.
For leaf symptoms that come with wet roots, see Alocasia brown spots. Our houseplant root rot guide compares rot across plants, and the Alocasia hub lists our other Alocasia pages.
References
- RHS: Alocasia Growing Guide
- NC State Extension Gardener Plant Toolbox: Alocasia
- NC State Extension Gardener Plant Toolbox: Alocasia × mortfontanensis
- University of Maryland Extension: Root Rots of Indoor Plants
- Clemson Cooperative Extension HGIC: Houseplant Diseases & Disorders (HGIC 2251)
- RHS: Leaf Damage on Houseplants
How this guide was put together: RHS, NC State Extension, University of Maryland Extension and Clemson Cooperative Extension HGIC guidance.