Ierburile aromatice sunt pe balcon.

Because ierburile means the herbs, while ierburi means just herbs.

• iarbă = herb / grass (singular)
• ierburi = herbs (plural, indefinite)
• ierburile = the herbs (plural, definite)

Romanian usually adds the definite article to the end of the noun, instead of putting a separate word like English the in front.

So:

• ierburi aromatice = aromatic herbs
• ierburile aromatice = the aromatic herbs

This is just the normal plural form of this noun, and it is irregular enough that you need to learn it as a pair:

• iarbă = herb / grass
• ierburi = herbs

Romanian plurals are not always formed in one simple way. Many nouns change their ending, and sometimes the stem changes too. So for learners, it is best to memorize nouns with their plural:

• iarbă – ierburi

In Romanian, adjectives usually come after the noun.

So the normal order is:

• ierburile aromatice = the aromatic herbs

This is different from English, where adjectives usually come before the noun:

• the aromatic herbs

Romanian can sometimes place the adjective before the noun, but that is less neutral and often sounds more literary, emphatic, or stylistically marked. In an ordinary sentence like this, noun + adjective is the standard order.

Because the adjective has to agree with the noun.

Here, ierburile is plural, so the adjective also has to be plural:

• singular: iarbă aromatică = aromatic herb
• plural: ierburi aromatice = aromatic herbs
• definite plural: ierburile aromatice = the aromatic herbs

So aromatice matches a plural noun here.

Sunt is the 3rd person plural form of a fi, which means to be.

So:

• eu sunt = I am
• ei/ele sunt = they are

In this sentence, the subject is ierburile aromatice (the herbs), which is plural, so Romanian uses sunt = are.

Because pe means on, and a balcony is understood as a surface or open platform, so Romanian says pe balcon = on the balcony.

Compare:

• pe balcon = on the balcony
• în cameră = in the room
• în bucătărie = in the kitchen

So Romanian treats balcon differently from enclosed spaces like a room or kitchen.

Romanian does not use a separate word like English the. Instead, definiteness is often shown in other ways.

Also, after prepositions, Romanian very often uses a bare noun in common location expressions where English uses the:

• în casă = in the house / at home
• la școală = at school
• pe balcon = on the balcony

So pe balcon is completely natural Romanian, even though English usually says on the balcony.

If you wanted to make it more explicitly definite in another context, Romanian could use something like:

• pe balconul apartamentului = on the apartment’s balcony

But in a simple sentence like this, pe balcon sounds normal.

The singular iarbă can mean grass or herb, depending on context.

But the phrase ierburi aromatice specifically means aromatic herbs, so here the meaning is clearly herbs, not grass.

That is a very common Romanian expression for culinary or fragrant herbs.

Yes, Romanian word order is fairly flexible, but the original sentence is the most neutral one:

• Ierburile aromatice sunt pe balcon.

You could also say:

• Pe balcon sunt ierburile aromatice.

That version puts more focus on pe balcon (on the balcony), as if answering Where are the herbs?

So the original order is the basic, neutral one: subject + verb + place

The singular would be:

• Iarba aromatică este pe balcon.

This means The aromatic herb is on the balcony.

Compare:

• iarba aromatică este = singular
• ierburile aromatice sunt = plural

So both the noun, adjective, and verb change to match singular or plural.