Polka dot begonia leaves turning yellow: causes and what to do
17 results in the diagnosis tree begin with yellowing leaves, 7 of them marked likely when the answers fit. They are ordered here for Polka dot begonia (Begonia maculata), using what its sources say about soil moisture, light, soil, watering and feeding and 2 problems recorded for it.
Sources last read 14 September 2026.
Begonia maculata, the polka dot begonia, is a species of begonia native to southeast Brazil. It grows naturally in the understory of the Atlantic rainforest, with occurrences confirmed in the Brazilian states of Espírito Santo and Rio de Janeiro. Wikipedia, CC BY-SA 4.0
Native range: Brazil (Rio de Janeiro) (wet tropical). Also sold as trout begonia.
What Polka dot begonia’s sources say that bears on this
- Soil moisture
- Moist but well-drained or Well-drainedRHS · read 13 September 2026
- Light
- Partial shadeRHS · read 13 September 2026
- Soil
- Clay, Loam, Sand; pH Acid or NeutralRHS · read 13 September 2026
- Watering
- Does not cope with constant direct sun or with waterlogging. During growth, water moderately and give a balanced liquid fertiliser at every other watering.RHS · read 13 September 2026
- Feeding
- While growing, water moderately, adding a balanced liquid fertiliser at every other watering.RHS · read 13 September 2026
How this shows up on a Polka dot begonia
Pale, undersized leaf blades at the tips of the stems
The newest leaf blades on the polka dot begonia are the palest and smallest, and the stems carrying them bend toward the brightest side of the room.
Partial shade is where its source places it. Below that the plant spends stored sugar faster than it makes it, and reaching is what that looks like from outside.
Telling it apart: Whether it leans. A plant reaching for a window is answering a light question, and it leans before it pales.
RHS · read 13 September 2026Yellow, limp leaf blades at the base
Yellow spreads upward through the polka dot begonia a few leaf blades at a time, and the compost darkens and stays cold to the touch.
Soil described as moist but well-drained or well-drained is a drainage instruction as much as a watering one. Compost that stays saturated suffocates the fine roots that do the drinking.
Telling it apart: The soil, not the leaf. Wet compost under yellowing leaves points one way and dry compost the other, and the leaves alone will not tell you which.
RHS · read 13 September 2026Possible causes, likeliest first for a Polka dot begonia
Most likely cold
Ranked higher because Polka dot begonia's recorded problems point this way.
Its RHS hardiness rating puts this plant's cold floor at 10°C or above, so a cold windowsill at night is a strong explanation.
- H1B — 10–15°C RHS · read 13 September 2026
Why: Soft, dark patches rather than crisp ones are damaged tissue rather than dried tissue.
What to try:
- Move it away from the glass at night, or keep the curtain on the room side of the polka dot begonia.
- Leave damaged leaves until new growth appears, then remove the worst of them.
What would settle it: Where the polka dot begonia sits at night, and what the glass feels like at that hour. Damage that appeared after one cold night, on the side facing the window, is the pattern.
Most likely not enough light
Ranked higher because Polka dot begonia's recorded problems point this way.
- Partial shade RHS · read 13 September 2026
Why: Far from a bright window, a polka dot begonia builds leaves it cannot afford.
What to try:
- Move it closer to the brightest window you have, over a week or two rather than in one step.Useful: grow light
- Water less while it is in low light; a polka dot begonia that is barely growing uses little.
What would settle it: Compare a new leaf with one from last year. Smaller and paler, with a longer gap below it, is the reaching pattern rather than a nutrient one.
Most likely too little water
- Moist but well-drained or Well-drained RHS · read 13 September 2026
Why: Soil dry two inches down, under lower leaves that are yellowing or leaves that are falling, is a polka dot begonia shedding what it cannot support.
What to try:
- Water until it runs from the drainage hole, then let the pot drain.Useful: pot with drainage holes
- If the water runs straight through a shrunken rootball, stand the pot in water for twenty minutes so the compost can take it up.
What would settle it: Water it thoroughly and look again the same evening. A thirsty plant firms up fast. One that does not has a root problem rather than a water problem.
Less likely for a Polka dot begonia, still possible
- Most likely short of nutrients
- Most likely too much water
- Most likely a build-up of salts in the soil
- Light and feeding are both plausible, and this does not separate them
- Nutrients are an unlikely explanation here
- Possibly root rot, in a pot that has stopped draining
- Possibly too much direct sun
- Possibly too much direct sun, or feeding
- This may be ordinary leaf loss
- Probably too much water, but this is not settled
- Possibly dry air
- Probably too much water
- The answers do not point at one cause
Questions
- What usually causes yellowing leaves on a Polka dot begonia?
- For Polka dot begonia: most likely cold, most likely not enough light and most likely too little water. Its RHS hardiness rating puts this plant's cold floor at 10°C or above, so a cold windowsill at night is a strong explanation.
- How can I tell which one it is on my Polka dot begonia?
- Where is the yellowing? The lowest leaves, working upward; New growth at the top, while older leaves stay green; Between the veins, the veins themselves still green; At the leaf tips and edges, browning as it goes; Patchy, only on the side facing the window.
- What do Polka dot begonia's sources say about its soil moisture?
- RHS: Moist but well-drained or Well-drained.
- What does this look like on a Polka dot begonia?
- The newest leaf blades on the polka dot begonia are the palest and smallest, and the stems carrying them bend toward the brightest side of the room. Telling it apart: Whether it leans. A plant reaching for a window is answering a light question, and it leans before it pales.
- Is Polka dot begonia safe to handle while I check it?
- Its sources list it as toxic to cats and dogs. Wash your hands after handling the roots or sap, and keep trimmings away from pets.
Other plants that show yellowing leaves
AlocasiaThe crown yellows from below and the pot stays heavy
Arrowhead plantNew leaf blades arrive smaller and paler than the ones below
Asparagus fernPale, undersized fronds at the tips of the stems
Baby rubber plantYellowing that begins at the lowest leaves
Baby's tearsYellow, limp leaves at the base
Bird's nest fernYellowing that begins at the outermost blades
Something else wrong with the Polka dot begonia?
What this does not cover
This page orders a decision tree's results using a plant's sourced care. It has not seen your plant, its pot or its window, and two problems at once are common: that is the usual reason a confident answer turns out wrong. The questions in the diagnosis tool narrow it further than a list can.