White spots on underside of leaves of Chinese Money Plant (Pilea peperomioides)

(Question)

My Chinese Money Plant, which is about 18″ tall, has been healthy since I planted it from a 4″ cutting three years ago. It has continued to sprout new leaves both at the bottom and the top, and is quite full. This week, I noticed small white spots on the underside of many of the leaves. Some are scaly and can be removed by fingernail, but other appear to be developing inside the leaf before they appear. A couple of leaves are drooping. It is in a bathroom that gets mostly indirect, fairly bright light from a skylight; it might receive direct sun for a half hour per day. HELP!!

Thank you

(Answer)

Dear gardener, happy New Year and thank you for contacting us.

Chinese Money plants (Pilea peperomioides),not to be confused with Lucky Money Plants, are beautiful and generally, quite easy to grow houseplants. How wonderful that you have one!

In terms of light exposure requirements, your plant seems to be in an ideal location as it requires indirect light or partially shaded conditions (you mentioned half an hour of direct sun which is not bad unless the location gets longer exposure during the summer months, which may cause leaves scorching).

In terms of moisture, pileas do not like droughts but also dislike to sit in wet soil, and therefore, good drainage is essential. When leaves start drooping, it may be a sign of too much water (lower leaves droop) or need to water (upper leaves droop). But these are only possible indications.

As the plant originates at high altitudes in the South-Western Hunan province in China, it prefers cooler indoor temperatures. However, a sudden leaf drop may be a sign of a cold draft affecting this plant.

From the picture you sent us, and given the regular pattern of the spots, we think your plant may be suffering from oedema. This is a disorder affecting many succulents and semi-succulent plants caused by an imbalance in water when the roots take up more water than the leaves can transpire. This excess water ruptures the cells, particularly on the undersides, and leads to water-soaked patches which then become raised, warty or pimple-like swellings or growths. As they rupture, they can have a white, powdery appearance or may become rust-coloured and appear as scaly patches. Finally, corky spots or ridges may develop, particularly on woody plants.

Some of the causes of oedema are: excessively moist conditions in the soil or growing medium, in the atmosphere, or in combination, which give the plant cells an unusually high water content. Also, when foliage is reduced by the removal of leaves or shoots, plants have fewer transpiration surfaces to eliminate extra moisture.

I would suggest to check that the soil is free-draining. If plants are too wet, re-potting with fresh potting medium is advisable (some growers recommend to re-pot this plant every 2-3 years).  As new leaves develop, keep checking the soil and for more symptoms of stress but we think your plant will be ok. If however, conditions do not improve, please do not hesitate to contact us.

For your enjoyment, I have added an interesting article on the history of this beautiful plant:

www.wildchicken.com/nature/garden/ga008_a_chinese_puzzle.htm