Origano dobro raste u suhoj zemlji.

Because after u meaning in, Croatian uses the locative case for location.

So:

• basic form: suha zemlja = dry soil / dry earth
• after u: u suhoj zemlji = in dry soil

Both the adjective and the noun change because Croatian marks case on both:

• suha → suhoj
• zemlja → zemlji

This is a very common pattern in Croatian.

A useful contrast:

• u suhoj zemlji = in dry soil (location, so locative)
• u suhu zemlju = into dry soil (movement toward/into, so accusative)

Zemlji is locative singular here.

The noun zemlja is a feminine singular noun, and after u in the meaning in, it appears in the locative:

• zemlja = nominative singular
• zemlji = locative singular

So in this sentence, u suhoj zemlji is a prepositional phrase meaning in dry soil.

Because adjectives in Croatian must agree with the noun they describe in:

• gender
• number
• case

Here the noun is zemlji, which is:

• feminine
• singular
• locative

So the adjective must also be feminine singular locative:

• suha zemlja = dry soil
• u suhoj zemlji = in dry soil

That -oj ending is a common feminine singular ending in the dative/locative pattern.

Dobro here is an adverb, meaning well.

It describes the verb raste:

• raste = grows
• dobro raste = grows well

Since dobro is an adverb, it does not agree with a noun, so it does not change for gender, number, or case.

Compare:

• dobar origano = good oregano → adjective, so it agrees with the noun
• origano dobro raste = oregano grows well → adverb, so it stays dobro

Raste is the 3rd person singular present tense of rasti, meaning to grow.

Why 3rd person singular?

Because the subject is origano, which is singular:

• ja rastem = I grow
• ti rasteš = you grow
• on/ona/ono raste = he/she/it grows

So:

• Origano raste = Oregano grows

In this sentence, the present tense expresses a general truth or typical behavior, just like English Oregano grows well in dry soil.

Because Croatian has no articles like English a / an / the.

So Croatian simply says:

• Origano raste
  instead of
• The oregano grows

Whether something is definite or indefinite is usually understood from:

• context
• word order
• emphasis
• sometimes demonstratives like taj, ovaj, etc.

So the lack of the is completely normal.

Yes. Croatian word order is more flexible than English.

The sentence:

• Origano dobro raste u suhoj zemlji.

is a neutral, natural order.

But other orders are also possible, depending on emphasis:

• Origano raste dobro u suhoj zemlji.
• U suhoj zemlji origano dobro raste.

These all mean roughly the same thing, but the focus shifts slightly.

For example:

• U suhoj zemlji origano dobro raste puts more emphasis on in dry soil
• Origano dobro raste starts with the topic oregano

So the original sentence is just the most straightforward presentation.

Zemlja can mean several related things in Croatian, depending on context:

• earth
• ground
• land
• country
• soil

In this sentence, because we are talking about how oregano grows, zemlja clearly means soil.

So:

• u suhoj zemlji = in dry soil

Context is very important with this word.

Because when talking about something growing in soil, Croatian normally uses u.

So:

• u zemlji = in the soil / in the ground

Using na would usually suggest on a surface, not inside or within the soil.

So for plants, roots, and growing conditions, u is the natural choice here.

A rough English-friendly pronunciation is ZEM-lyi.

The tricky part is lj, which is a single Croatian sound. It is somewhat similar to the lli in million for many English speakers, though not exactly the same.

So:

• zemlji ≈ ZEM-lyi
• suhoj ≈ SOO-hoy
• raste ≈ RAHS-teh

You do not pronounce lj as a hard separate l + j in slow English style; it works more like one combined sound.

Here origano is simply the subject of the sentence, in its basic dictionary form.

So:

• Origano dobro raste = Oregano grows well

For a learner, the key thing in this sentence is that origano is the thing doing the growing, so it appears in the nominative singular.

With loanwords like this, it is best to learn their behavior from actual examples rather than guessing everything from the ending alone. In this sentence, you only need to recognize it as the subject.