Alocasia macrorrhizos ‘Black Stem’

The tropical background of Alocasia macrorrhizos ‘Black Stem’

The dark-stemmed ‘Black Stem’ selection belongs to Alocasia macrorrhizos. The species is native to wet tropical regions from island Southeast Asia through New Guinea and the western Pacific to northern Queensland.

Growing Alocasia macrorrhizos ‘Black Stem’

• Light: Give ‘Black Stem’ bright filtered light; acclimatise it slowly if you add stronger sun.
• Watering: During active growth, check moisture deeper in the pot and water as those deeper parts begin to lose moisture, before the pot dries through. Water until excess runs from the drainage holes. Let the pot drain, then empty any water left in the saucer or cover pot.
• Potting mix: Use a fertile mix that stays loose and drains well after watering.
• Temperature: Keep ‘Black Stem’ warm while it is actively growing and move it away from cold glass or draughts before the temperature falls to 15 °C.
• Feeding: While new leaves are actively growing, feed according to the fertiliser label. If the label gives a range, choose the more frequent option. Stop when growth slows.
• Humidity: Alocasia does best with medium to high humidity. Keep it in a bright spot away from heaters and air-conditioning. If the air is dry, place it near other houseplants that like similar conditions, leaving space between the leaves, or use a clean humidifier.

Alocasia macrorrhizos ‘Black Stem’: problems and fixes

• New leaf stalks stretch and weaken as the plant grows towards the window: Shift it to a brighter position without exposing it to harsh direct sun. When light comes mainly from one side, rotate the pot gradually so future growth develops more evenly. Mature stretched stalks will stay long.
• Several leaves yellow after the plant has been chilled and the mix is still damp: Put the plant back in a consistently warm spot and give the damp root ball time before watering again. If the decline continues or the base becomes soft, examine the roots for damage.
• Dry brown margins appear again and again: Compare the current watering rhythm with earlier weeks, and check for hot, dry air or salt build-up from water and fertiliser. Correct the cause that fits rather than simply watering more often.
• Fine pale speckles spread over the leaves: Turn over several leaves and inspect the veins for moving spider mites or webbing. Once the pest is confirmed, isolate the plant. Use a treatment labelled for spider mites on indoor ornamental plants, and repeat it only as directed on the label.

Alocasia macrorrhizos ‘Black Stem’: toxic if chewed

• Pets: This Alocasia is toxic to cats and dogs. Keep the plant and any cut pieces where pets cannot chew them.
• Children and handling: Keep it out of reach of children. Sap from damaged tissue can irritate skin and eyes, so wash your hands after pruning and avoid touching your face.
• Why it irritates: Alocasia tissue contains insoluble calcium oxalate crystals. Chewing or contact with sensitive tissue can cause immediate local irritation.
• Possible symptoms: Mouth exposure can cause burning pain, drooling, swelling, nausea or vomiting, and difficulty swallowing.
• After exposure: For a pet, contact a veterinarian. For a person, remove any plant material from the mouth and rinse with water; seek medical or poison-control advice if symptoms are significant. Breathing difficulty or rapidly increasing swelling needs urgent medical attention.

What macrorrhizos means in ‘Black Stem’

Macrorrhizos means “large-rooted”, combining Greek makros, “large” or “long”, with rhiza, “root”. ‘Black Stem’ is the horticultural name used for the dark-petioled form.