How to Care for Begonia Looking Glass in Hong Kong | Plantjai

References

1. American Begonia Society. Rex Begonias. https://www.begonias.org/
2. RHS. Begonias as Houseplants. https://www.rhs.org.uk/plants/begonias/houseplants
3. ASPCA. Begonia – Toxic and Non-Toxic Plants. https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/begonia

⚠️ Toxicity warning: Looking Glass contains calcium oxalate crystals throughout the plant and is toxic if ingested, potentially causing oral irritation and gastrointestinal upset in both humans and pets. Keep out of reach of children and pets, and wash your hands after handling.

In-depth care guide

Introduction

Looking Glass is a striking member of the Rex-cultorum group, the vast collection of ornamental begonia hybrids descended from Begonia rex, originally native to the humid subtropical hills of Assam. What sets Looking Glass apart even within this dazzling group is the sheer scale and intensity of its silver colouring — broad, silvery-white leaves traced with olive-green veins, paired with a deep wine-red underside that gives the cultivar its evocative name. Under the right light, the effect really is like looking into a slightly imperfect antique mirror.

Like all Rex-cultorum begonias, Looking Glass is a rhizomatous plant, growing from a thick, creeping underground or surface-level stem rather than a conventional upright trunk. This rhizome anchors the plant and stores reserves of water and energy, but it's also the single greatest vulnerability in cultivation — persistent moisture around the rhizome leads to rot far more readily than most growers expect, often catching new begonia keepers off guard.

Light requirements

Looking Glass needs bright, diffused light to develop and maintain its signature metallic sheen. An east-facing windowsill, catching gentle morning sun, is ideal, as is a position a few steps back from a south-facing window where the light has been softened by distance or a sheer curtain. Aim for roughly 1,500–3,000 lux at the leaf surface if you want to measure it precisely with a light meter app.

Direct sun is the clearest danger here — even a short period of harsh midday light will scorch the leaves and fade the silvery colouring, undermining the very quality that makes this cultivar desirable. On the flip side, insufficient light causes the colour to turn flat and dull, and the plant becomes loose and leggy as it stretches toward whatever light is available. Rotating the pot a quarter turn weekly helps maintain an even, balanced shape as the plant naturally leans toward its strongest light source.

Watering

Water once the topsoil has dried out to a depth of about 2–3 cm, typically every 5–7 days during active growth. Rather than watering on a fixed schedule, use the finger test or simply lift the pot to gauge its weight — both are more reliable indicators of actual soil moisture than the calendar. Keep the soil evenly, lightly moist at all times, but never let it become waterlogged.

Water should always go directly onto the soil rather than over the foliage, since moisture sitting on the leaves creates ideal conditions for fungal growth. After a thorough soak, empty any water that collects in the saucer promptly — Rex begonias are notably prone to rot, and even a short period of standing water can cause lasting damage to the rhizome. Use room-temperature water, and if your tap water is heavily chlorinated or mineral-rich, consider filtered water or rainwater instead.

Soil and pot

This cultivar needs a light, loose, exceptionally well-draining substrate. A useful mix combines peat-free potting soil with perlite and fine orchid bark (roughly 1/8–1/4 inch pieces) to maximise airflow around the shallow root system. Because the rhizome spreads horizontally along the soil surface rather than growing deep, a wide, shallow pot is far more suitable than a deep one.

The pot must have drainage holes, and terracotta is generally the better choice over plastic for the additional breathability it offers. When repotting, position the rhizome so it sits slightly proud of the soil surface rather than buried, which helps prevent the moisture buildup that leads to rot. If you'd prefer to use a decorative pot without drainage, keep the plant in its original growing pot and simply nest that inside the decorative cachepot, removing it to drain after watering.

Temperature and humidity

Looking Glass grows best between 18°C and 24°C. Prolonged exposure to temperatures below 18°C can trigger dormancy, so keep the plant away from cold drafts, particularly during Hong Kong's cooler winter months near windows and doors. Humidity should ideally sit between 50% and 70%, which can be maintained with a pebble tray or humidifier as needed.

Keep the plant well away from AC vents, heating units, and drafty gaps around doors and windows. Good air circulation matters just as much as humidity — stagnant, warm, humid air is the perfect breeding ground for powdery mildew, one of the most common issues affecting this cultivar. Avoid misting the leaves directly, since damp foliage is itself a magnet for fungal problems; grouping the plant with other foliage plants is a safer way to raise ambient humidity naturally.

Common problems in detail

Dulling silvery sheen results from light that's either too strong or too weak — adjust to a stable position with bright, diffused light, avoiding both harsh direct sun and dim corners.

Powdery mildew, showing as a white powdery film on the leaves, stems from poor air circulation combined with excess humidity — trim off badly affected leaves, improve airflow, and consider a preventive spray of diluted baking soda solution (1 tablespoon baking soda, 3 drops dish soap, 1 gallon water) every 10–14 days.

Rhizome rot typically follows overwatering or a rhizome planted too deep — reduce watering frequency, check the rhizome's position relative to the soil surface, and repot if necessary.

Winter leaf drop is usually triggered by shorter days and cooler temperatures inducing semi-dormancy — reduce watering, keep the plant warm, and allow it to recover naturally once spring arrives; resist the urge to overwater in an attempt to revive it.

Scorched, crisp leaf edges point to humidity that's too low or fertiliser applied too concentrated — raise ambient humidity and always dilute fertiliser to half the recommended strength.

Water-marked spots on the leaves come from splashing during watering — switch to watering along the pot's rim to keep the foliage consistently dry.

Toxicity information

Looking Glass contains calcium oxalate crystals throughout the plant, and is toxic if chewed or ingested by either humans or pets, potentially causing oral irritation and gastrointestinal upset. Keep the plant well out of reach of children and pets, and wash your hands thoroughly after handling or pruning.

References

• American Begonia Society. Rex Begonias. https://www.begonias.org/
• RHS. Begonias as Houseplants. https://www.rhs.org.uk/plants/begonias/houseplants
• ASPCA. Begonia – Toxic and Non-Toxic Plants. https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/begonia
• Missouri Botanical Garden. Begonia rex-cultorum Group. Plant Finder. http://www.missouribotanicalgarden.org/PlantFinder/