Novi krumpir je bolji od starog krumpira.

Because novi has to agree with krumpir in gender, number, and case.

• krumpir is masculine singular
• here it is in the nominative case, because it is the subject of the sentence
• so the adjective also takes the masculine singular nominative form: novi

So:

• novi krumpir = new potato / new potatoes in a general sense

If the noun changed case, the adjective would change too.

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

So:

• Novi krumpir je bolji... = New potatoes are / new potato is better...

Croatian often uses je where English uses is. In this sentence it links the subject novi krumpir with the description bolji od starog krumpira.

Because the comparative of dobar = good is irregular.

• dobar = good
• bolji = better
• najbolji = best

This is similar to English:

• good
• better
• best

So bolji is simply the correct comparative form to memorize.

Od is used to mean than in comparisons.

So:

• bolji od... = better than...
• veći od... = bigger than...
• brži od... = faster than...

In Croatian, after od, the following noun usually goes into the genitive case.

That is why the sentence has:

• od starog krumpira

and not:

• od stari krumpir

Because od requires the genitive case.

The noun krumpir changes from nominative to genitive:

• nominative: krumpir
• genitive: krumpira

And the adjective must match it:

• nominative masculine singular: stari
• genitive masculine/neuter singular: starog

So:

• od starog krumpira = than old potatoes / than the old potato crop

This is a very common pattern in Croatian: a preposition changes the case of the noun, and the adjective changes with it.

Yes, Novi krumpir je bolji od starog is possible if the meaning is clear from context.

Croatian often repeats the noun for clarity:

• Novi krumpir je bolji od starog krumpira.

But once the topic is obvious, speakers may shorten it:

• Novi krumpir je bolji od starog.

Here starog means something like the old one / the old kind / the old potatoes, with the noun understood.

So the full version is clearer for learners, but the shorter version can sound natural too.

Not exactly. In this context, novi krumpir usually means new potatoes: freshly harvested, young potatoes.

Likewise, stari krumpir often means old potatoes in the sense of potatoes from an older harvest, not necessarily rotten or unusable.

So this is often about freshness / season / harvest age, not just the basic dictionary meanings of new and old.

Grammatically, krumpir is singular in form here. But Croatian often uses singular mass or collective-style nouns where English may prefer a plural.

So Novi krumpir je bolji od starog krumpira can be understood as:

• New potatoes are better than old potatoes
• or more literally, New potato is better than old potato

English naturally prefers the plural in this meaning, but Croatian can express it with singular krumpir.

Because bolji agrees with the subject novi krumpir.

The subject is:

• krumpir = masculine singular

So the comparative adjective is also:

• bolji = masculine singular

Compare:

• Novi krumpir je bolji.
• Nova juha je bolja.
• Novo vino je bolje.

So the ending changes depending on the gender of the noun being described.

Yes, Croatian word order is more flexible than English, but not every version sounds equally neutral.

The most neutral order here is:

• Novi krumpir je bolji od starog krumpira.

You might also hear variations for emphasis, for example:

• Bolji je novi krumpir od starog krumpira.
• Od starog krumpira novi krumpir je bolji.

These can sound more marked or stylistically different. For a learner, the original sentence is the best basic pattern to remember.

No. Krumpir is common, especially in many parts of Croatia, but another very common word is krumpir’s regional alternative krompir, especially in some neighboring varieties and regions.

Within standard Croatian, krumpir is the usual form to learn.

So in this sentence, krumpir is exactly what you should expect in standard Croatian.