One way to hold this word: plant + -er, the one that does the planting. The -er does not care who or what it is. It can be a person bending down to put a seedling in the soil. It can be a machine dragged behind a tractor, dropping seeds row after row. It can be someone who owns a whole of tea and lives off what is planted there. And the big container on a doorstep sits on the same line: it is the place the planting goes into, so it takes the same name. This is a picture to hold the word together, not a claim about how the word grew.
From the word’s history
Wiktionary's etymology tree for planter runs plant + -er, with -er going back through Old English -ere and Latin -arius.
Wiktionary 的字源樹顯示 planter 就是 plant 加上 -er，而 -er 這個字尾可以一路追到古英語 -ere 和拉丁語 -arius。這正好對上今天的用法：不管是人、機器還是容器，都掛在「種」這個動作旁邊。
Wiktionary entry for planter (kaikki extract, source_ref kaikki:3f6f69a190036ae4:1328198891:18736), etymology tree: English plant + English -er
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