Scale insects go through numerous life stages, some of which are easier to see and some that are more vulnerable to removal. These cycles occur repeatedly during a year on indoor plants, with multiple stages potentially occurring on a plant at one time.

Scale insects do not intentionally inhabit the soil, but they may be present in an unexpected (or difficult to see) form on your plant. For that reason, the removal process is difficult and requires patience and repetition.

The step that you took, completely removing all visible scale manually, is exactly the right approach. You will need to continue to inspect the plant every 7 to 14 days for signs of scale and repeat the physical removal process.

If you bring your plant indoors, keep it away from other plants until it has been inspected repeatedly over a period of months and no scale is found. A full insect life cycle is about two months long so that is a reasonable "all clear" test period if you are keeping a really close eye on the plant. Good luck!

Courtesy of NYBG Plant Information Service