Learn Hardcore Italian: Sul balcone cresce il basilico, a cui aggiungo acqua ogni sera. - On the balcony grows the basil that I add water to every evening.

“Cresce” is the third-person singular present tense of crescere (“to grow”). We use the singular form because the subject, il basilico, is singular. If you were talking about multiple plants, you’d say “sui balconi crescono i basilici” (though in practice Italians usually speak of the plant species in the singular).

What is the function of “sul” in “sul balcone”, and why not “su il balcone”?

In Italian, many prepositions contract with the definite article: su + il becomes sul. So “sul balcone” literally means “on the balcony.”

What does the compound “a cui” mean in this sentence?

“A cui” is a relative pronoun meaning “to which” (or “to which one”). It refers back to “il basilico.” In English you’d say “the basil to which I add water every evening,” but we usually simplify it to “the basil I water every evening.”

Why is it “a cui aggiungo acqua” instead of “che aggiungo acqua”?

The verb aggiungere (“to add”) requires the preposition a before the object you’re adding to: aggiungere acqua a qualcosa. When you turn a + che into a relative form, che cannot carry a preposition, so you use cui instead. Hence “a cui aggiungo”.

Why is there no article before “acqua”?

When talking about a substance in a general sense (mass noun), Italian often omits the article. If you said “aggiungo l’acqua”, it would imply a specific water previously mentioned. Here, “acqua” simply means “water” in general.

How does “ogni sera” work in this sentence?

“Ogni sera” is an adverbial phrase of frequency meaning “every evening.” It tells us how often you add water and is placed after the verb phrase, just like in English: “I add water every evening.”

Could you replace “a cui” with “che” if you changed the wording?

Yes. If you rephrase to avoid the preposition, for example:
• “Sul balcone cresce il basilico. Io gli aggiungo acqua ogni sera.”
Here “gli” (to it) replaces “a cui,” and each clause stands independently. You lose the single-sentence relative structure but keep the meaning.