Learn Hardcore Indonesian: Ibu mengurus tanaman di balkon. - Mother takes care of the plants on the balcony.

Your own mother (Mom/Mother). Capitalizing Ibu is common in writing when referring to one’s own mother.
A respectful title for an adult woman, like Mrs./Ma’am (often followed by a name: Ibu Sari).

Lowercase ibu is the common noun “mother” in general. In this sentence, with no name, it most naturally reads as “Mom/Mother.”

Can I use Bu instead of Ibu?

Bu is the vocative/short form used to address someone: “Bu, sebentar ya.” As a subject in a sentence, use Ibu, not Bu. You’d say “Ibu mengurus tanaman…”, but when calling her, “Bu, tolong…”.

Does di balkon tell me where Mom is, or where the plants are?

It can do either, and usually that’s fine because both are true. If you need to be explicit:

To modify the plants: Ibu mengurus tanaman yang ada di balkon.
To stress Mom’s location: Ibu mengurus tanaman di balkon already works, but you can front it: Di balkon, Ibu mengurus tanaman.

Is mengurus the best verb for “taking care of” plants? What about merawat, memelihara, etc.?