Learn German: Ich stelle die Pflanze auf den Balkon. - I am putting the plant on the balcony.

In German, you have to be specific about how you put something down. Stellen means to place something in an upright or standing position. Since a potted plant stands upright, we use stellen. If you were laying a book flat on a table, you would use legen.

Why is it auf den Balkon (accusative) and not auf dem Balkon (dative)?

Auf is a two-way preposition. Because you are actively moving the plant onto the balcony (showing direction or a change of location), you must use the accusative case (den). If the plant were already just sitting there, you would use the dative case to describe its fixed location: Die Pflanze steht auf dem Balkon.

Can I just use tun for "put" here?

It is highly recommended not to! English uses "put" for almost everything, but German requires specific placement verbs like stellen, legen, or setzen. While you might hear native speakers use tun for "put" in casual slang, stellen is the correct and natural way to say you are putting an upright object down.

Does den Balkon mean that the word Balkon is masculine?