How to Fix Yellow Leaves and Root Rot in Alocasia (Dumb Cane): A Detailed Guide to Growing Methods and Precautions

Alocasia macrorrhizos (giant taro) is a very common household green potted plant these days, with broad, glossy leaves and strong ornamental value. Because it is a tropical plant, it generally does not bloom in the north, but if the temperature, humidity and other conditions at home are suitable, it may also flower. Its full bloom period is from February to April, while from November to May or June of the following year it is in a dormant period. To grow it well, you need to put effort into light, temperature, and water and fertilizer.

Light and temperature: 3-5 hours of sun a day, and remember to bring it indoors in winter

Alocasia macrorrhizos likes a warm, humid environment with slight shade. During the growing season it is best placed in a shaded spot on a balcony or in a courtyard, where it can get both shade and ventilation; never expose it to direct sunlight in summer. However, once the flowering period arrives, you must ensure sufficient sunlight, otherwise the spathe will take on a green tint and its quality will suffer. Normally, ensure 3-5 hours of light per day; with insufficient light the leaf stalks tend to stretch out, and its ornamental value is reduced.

As for temperature, the optimal growing temperature for Alocasia macrorrhizos is 20-25°C; it can grow normally within the range of 20-30°C, and can tolerate a low of 8°C, but its cold tolerance is not strong, so by mid-October each year it must be moved into a greenhouse or indoors for care. During high summer temperatures, while providing shade, spray water frequently to cool it down and keep it moist; the air humidity should preferably be no lower than 60%. In winter, control watering; spraying warm water once a week is enough to keep the leaves dark green, as too much water easily causes root rot.

Water, fertilizer and soil: heavy feeding and heavy watering, small amounts but frequent

Alocasia macrorrhizos naturally likes moist, fertile soil, which is what farmers often call "heavy feeding and heavy watering." During the growing period, water in small amounts but frequently, keeping the potting soil moist at all times, and be sure to water thoroughly rather than just wetting the soil surface. It is not very demanding about soil, but it does best in well-drained, organic-rich sandy loam or humus loam. You can also mix leaf mold, peat soil, river sand and a small amount of thoroughly rotted cake fertilizer into a nutrient soil, or simply grow it in water.

It is fairly fond of fertilizer. From March to October, apply a liquid fertilizer once every half month, and the proportion of nitrogen can be appropriately increased. You can also apply a dilute liquid fertilizer based mainly on nitrogen mixed with phosphorus and potassium once or twice a month. When the temperature drops below 15°C, stop fertilizing; in winter, likewise stop fertilizing and control watering.

Water culture method: new roots in 3 days, change the nutrient solution in 3 weeks

Before growing Alocasia macrorrhizos in water, first remove the yellow leaves and rotten roots. If the tuber has not yet grown roots, leave it in a shaded place to dry for 2-3 days before putting it in water. After planting, add clean water, immersing two-thirds of the root system; change the clean water once every 2-3 days, and generally new roots will grow after 3 days. After 3 weeks, switch to a nutrient solution for care, replacing it about once every 4 weeks. Each time you change the water or nutrient solution, rinse the tuber and the mucus on it with clean water, and remove any rotten roots while you are at it.

What to do about yellow leaves? Match one of these 5 causes

First, red spider mites. Check whether there are white dots on the leaf surface; if it feels rough, has a waxy texture and lacks shine, then it is red spider mites. Wash with soapy water twice, with two days between each treatment, and it will be solved. Second, the soil is too poor and lacks nutrients; promptly supplement with nitrogen and phosphorus fertilizers and organic fertilizer. Third, frost damage in winter: Alocasia macrorrhizos is suited to a warm, humid climate, and if left outdoors for a long time in winter its leaves are easily frost-damaged and turn yellow, so move it indoors to a spot with a constant temperature and plenty of light. Fourth, a heavy buildup of dust on the leaves blocks light absorption and causes yellow leaves, so regularly wipe the leaves with clean water as part of its care. Fifth, not watering for a long time: drought causes the leaves to turn yellow, so keep the soil moist at all times.

Finally, a special reminder: although the corms and leaves of Alocasia macrorrhizos can be used medicinally, they are highly toxic, and the leaf sap will cause poisoning if ingested. If you have pets or children at home, it is not suitable to grow Alocasia macrorrhizos, to avoid tragedy; this is the most important point to note when growing it.