Blizina prozora je važna za biljku.

Blizina means closeness, nearness, or proximity.

In this sentence, blizina prozora means the closeness to the window or more naturally in English, being near the window.

It is a noun, not an adverb. Compare:

• blizu = near
• blizina = nearness / proximity

So Croatian is using a noun phrase where English might often prefer a different structure, such as Being near the window is important for the plant.

Because prozora is the genitive singular form of prozor.

The noun blizina often takes the thing that is being approached or measured in the genitive:

• blizina grada = the proximity of the city / closeness to the city
• blizina škole = closeness to the school
• blizina prozora = closeness to the window

So:

• nominative: prozor = window
• genitive: prozora = of the window / to the window

This is very common in Croatian: one noun can require another noun in a certain case.

Because biljku is the accusative singular form of biljka.

After za meaning for, Croatian often uses the accusative:

• za dijete = for the child
• za kuću = for the house
• za biljku = for the plant

So here:

• nominative: biljka = plant
• accusative: biljku = plant, as the object after za

Because važna agrees with blizina, which is a feminine singular noun.

In Croatian, adjectives must agree with the noun they describe in gender, number, and case.

Here:

• blizina = feminine singular
• therefore: važna = feminine singular form of important

Compare:

• važan = masculine singular
• važna = feminine singular
• važno = neuter singular

So the sentence literally matches as:

• Blizina ... važna
• Closeness ... important

Je is the 3rd person singular present tense of biti = to be.

So:

• je = is

The sentence structure is:

• Blizina prozora = closeness to the window
• je = is
• važna = important
• za biljku = for the plant

So it works like:

Closeness to the window is important for the plant.

Yes, it is grammatical and understandable, but it sounds a bit formal or abstract because of the noun blizina.

In everyday speech, Croatians might also say things like:

• Biljci je važno da bude blizu prozora. = It is important for the plant to be near the window.
• Važno je da biljka bude blizu prozora. = It is important that the plant be near the window.

So your sentence is fine, but it has a slightly more formal or textbook-like feel.

Yes. Croatian word order is more flexible than English.

For example, you could also say:

• Za biljku je važna blizina prozora.
• Blizina prozora važna je za biljku.

These all mean basically the same thing, but the emphasis changes slightly.

The original version is neutral and clear:

• Blizina prozora je važna za biljku.

If you move za biljku to the front, you emphasize for the plant a bit more.

Yes, very naturally.

A common alternative is:

• Blizina prozora je važna biljci.

Here biljci is the dative singular of biljka, and it means something like to the plant.

Croatian often expresses important to someone/something with the dative:

• To mi je važno. = That is important to me.
• Djeci je to važno. = That is important to the children.
• Biljci je važna blizina prozora. = Proximity to the window is important to the plant.

So both are possible:

• važna za biljku
• važna biljci

The dative version often sounds especially natural.

Because Croatian has no articles.

English says:

• the window
• the plant
• a plant

Croatian simply says:

• prozor
• biljka

Whether it means a, the, or something more general depends on context.

So prozora could mean:

• of the window
• of a window

And za biljku could mean:

• for the plant
• for a plant

In this sentence, English usually uses the because the idea is specific in context.

Word-for-word, yes, it looks like the closeness of the window, but that would sound odd in English.

A better natural interpretation is:

• closeness to the window
• proximity to the window
• being near the window

This is a good example of why literal translation is not always the best way to understand a sentence. Croatian often uses a noun + genitive pattern where English may prefer to or a verbal phrase.

A simple pronunciation guide is:

BLI-zi-na PRO-zo-ra ye VAZH-na za BILY-ku

A few helpful notes:

• j is pronounced like English y, so je sounds like ye
• ž sounds like the s in measure
• lj is a soft sound, somewhat like lli in million for many English speakers

So:

• važna has the ž sound: VAZH-na
• biljku has lj: roughly BILY-ku

Here are the dictionary forms:

• blizina = closeness, proximity
• prozor = window
• biti = to be
• važan / važna / važno = important
• za = for
• biljka = plant

And in the sentence, the forms are:

• blizina = nominative singular
• prozora = genitive singular
• je = present tense, 3rd person singular of biti
• važna = feminine singular adjective
• za = preposition
• biljku = accusative singular

The subject is Blizina prozora.

More specifically:

• main noun: blizina
• dependent noun: prozora

So the sentence is saying that the nearness to the window is what is important.

This is why the adjective is feminine singular:

• blizina is the head noun
• važna agrees with blizina, not with prozor or biljka