kreskaĵo

Take it apart and it tells you everything. Kreski is to grow, and -aĵ- makes a concrete thing out of whatever it attaches to: manĝi to eat gives manĝaĵo food, trinki to drink gives trinkaĵo a drink, konstrui to build gives konstruaĵo a building. So a kreskaĵo is, quite literally, a thing that has grown. Meet the two halves and the word costs you nothing, which is what the affix system is for.

It is not the same word as planto. Planto is the botanist's word: a plant, a member of the plant kingdom, the thing you buy in a pot. Kreskaĵo is wider and vaguer, and deliberately so. It covers anything that grew: the plants in the border, yes, but also the moss on the wall, the weeds nobody planted, and - this is the sense that catches learners out - a growth in the medical sense, the lump the doctor wants a second look at. If you mean a plant, say planto. If you mean whatever that green stuff is, kreskaĵo is your word.

The rest of the family. Kresko (no -aĵ-) is growth as a process, the thing an economy does. Kreskigi is to make something grow, so a gardener kreskigas his beans. And elkreski is to grow out of something, which is how Esperanto says a habit outgrew you. One root, four everyday words, no new vocabulary.