Ako itko dođe ranije, neka ponese još jednu vreću zemlje za tulipane.

Because after ako (“if”), Croatian normally prefers the indefinite form itko for anyone.

• itko = anyone
• netko = someone

So:

• Ako itko dođe... = If anyone comes...
• Netko dolazi. = Someone is coming.

Using netko here is not impossible in casual speech, but itko is the more standard and natural choice after a conditional word like ako.

Because itko is grammatically singular. It literally means something like any one person.

So Croatian treats it as singular:

• itko dođe = if anyone comes

If you wanted to talk about multiple possible people, you would phrase the sentence differently.

After ako, Croatian very often uses the present tense of a perfective verb to talk about a future possible event.

So:

• Ako itko dođe... literally looks like If anyone comes...
• but it refers to a future possibility: If anyone comes/arrives (later, in that situation)...

This is very normal Croatian grammar. English also uses the present after if:

• If anyone comes early, ... not
• If anyone will come early, ...

Because dođe comes from the perfective verb doći, which focuses on a single completed arrival.

• dođe = comes/arrives as one whole event
• dolazi = is coming / comes regularly / is in the process of coming

In this sentence, the meaning is about a one-time event: if someone arrives earlier on that occasion. That is why dođe fits better.

Ranije means earlier. It is the comparative form of the adverb rano (early).

It usually means:

• earlier than expected
• earlier than usual
• earlier than the others

The comparison is understood from context, even though it is not stated explicitly.

Yes, this is a kind of third-person imperative or jussive construction.

Croatian does not really have a simple one-word imperative for he/she/they the way it has for ti or vi, so it uses:

• neka + present tense

So:

• neka ponese = let him/her bring, have them bring, or more naturally in English here, they should bring

In this sentence, it means: if anyone comes earlier, that person should bring the extra bag of soil.

Ponese comes from ponijeti, which means to take/carry along with you.
Donese comes from donijeti, which means to bring to a destination.

Here, ponese suggests:

• if someone comes early, they should take along an extra bag when they come.

Depending on context, donese could also be possible, but ponese emphasizes the idea of bringing it along with you.

Here još jednu means one more or another.

• još can mean still/yet, but in this context it means additional
• jednu = one in the feminine accusative singular form

So:

• još jednu vreću = one more bag / another bag

Because it agrees with vreću, which is:

• feminine
• singular
• accusative

The noun is vreća (bag, sack), and as the direct object of ponese, it goes into the accusative:

• nominative: jedna vreća
• accusative: jednu vreću

So both words change together.

Because vreća is a feminine noun, and here it is the direct object of ponese, so it takes the accusative singular form:

• nominative: vreća
• accusative: vreću

That final -u is a normal feminine accusative ending.

Because after a container noun like vreća (bag, sack), Croatian usually uses the genitive for the substance inside it.

So:

• vreća zemlje = a bag of soil
• literally: a bag of earth/soil

This is very common in Croatian:

• čaša vode = a glass of water
• boca vina = a bottle of wine
• vreća krumpira = a sack of potatoes

So zemlje is genitive singular after vreća.

Here it clearly means soil/earth.

The word zemlja can mean:

• earth/soil
• land
• country

But in the phrase vreća zemlje, the natural meaning is a bag of soil/earth. The context with tulips makes that especially clear.

Za here means for, and with that meaning it takes the accusative case.

So:

• za tulipane = for tulips

The noun tulipani changes here to tulipane because it is in the accusative plural.

This phrase tells us what the soil is intended for:

• soil for tulips
• not just any soil

Because Croatian often leaves out a subject when it is already clear from context.

In this sentence, the understood subject of neka ponese is the same person referred to by itko in the first clause.

So Croatian does not need to repeat something like taj netko or a pronoun. The meaning is already clear:

• if anyone comes earlier, that person should bring...

Because the sentence begins with a subordinate clause introduced by ako:

• Ako itko dođe ranije, ...

That clause is followed by the main clause:

• neka ponese još jednu vreću zemlje za tulipane.

In standard Croatian punctuation, this kind of if-clause is separated from the main clause with a comma.