Learn Spanish (Latin America): La planta es bonita, ¿la puedes regar hoy? - The plant is pretty, can you water it today?

Because you have a conjugated verb (puedes) combined with an infinitive (regar), you actually have two choices! You can place the pronoun before the conjugated verb (la puedes regar) or attach it to the very end of the infinitive (puedes regarla). Both are perfectly correct and mean the exact same thing.

Could I put the pronoun in the middle, like "¿puedes la regar hoy?"

No, you can never put the object pronoun between the conjugated verb and the infinitive. It must go either all the way at the front (la puedes regar) or attached directly to the end as one single word (puedes regarla).

What exactly does "la" mean here?

It translates to "it" and refers back to la planta. Because planta is a feminine singular noun, we must use the feminine singular direct object pronoun la to represent it.

Why do we use "es bonita" instead of "está bonita"?

Using es (from the verb ser) describes the plant's inherent, general characteristics. It means the plant is just a pretty plant overall. If you used está bonita (from estar), it would mean the plant looks especially pretty right now, perhaps because it just bloomed.