Compostul este bun.

In Romanian, the definite article is usually attached to the end of the noun instead of written as a separate word.

So:

• compost = compost
• compostul = the compost

The ending -ul is the masculine/neuter singular definite article here.

Because compostul means the compost, while compost by itself means compost in a more general or indefinite sense.

So:

• Compost este bun would not be the normal way to say Compost is good
• Compostul este bun = The compost is good
• Un compost bun = A good compost / good compost, depending on context

Romanian often requires the definite form when English uses the.

Este means is. It is the 3rd person singular form of a fi = to be.

So:

• Compostul este bun = The compost is good

In normal speech, Romanian often shortens este to e:

• Compostul e bun

Both are correct. Este sounds a bit more full or formal; e is very common in everyday speech.

Because compostul is masculine singular in this sentence, and the adjective agrees with it.

Romanian adjectives change form to match the noun in gender and number.

Here are some common forms of bun:

• masculine singular: bun
• feminine singular: bună
• masculine plural: buni
• feminine/neuter plural: bune

So:

• compostul bun = the good compost
• pâinea bună = the good bread

It is generally treated as neuter.

In Romanian, neuter nouns behave:

• like masculine in the singular
• like feminine in the plural

That is why in the singular you get:

• compostul este bun

But in the plural you would get:

• composturile sunt bune = the composts / the types of compost are good

So even though it is neuter, the singular adjective looks masculine: bun.

A simple learner-friendly approximation is:

kom-PO-stul ES-te boon

A few notes:

• c before o sounds like k
• o is a clear o, not like the English diphthong in some accents
• u in bun sounds like oo in good or put, but often a bit tenser/clearer
• este is pronounced roughly ES-te

If shortened:

• Compostul e bun ≈ kom-PO-stul e boon

Yes, but Compostul este bun is the most neutral and standard order.

Romanian word order is fairly flexible, but changes in order can affect emphasis.

For example:

• Compostul este bun = neutral statement
• Bun este compostul = marked/literary/emphatic, not the usual everyday order
• Este bun compostul = possible in context, often with special emphasis

For most learners, the safest choice is the standard order: subject + verb + adjective.

No, in a normal present-tense sentence like this, Romanian keeps the verb to be.

So you say:

• Compostul este bun
• or more commonly, Compostul e bun

You do not normally say:

• Compostul bun to mean The compost is good

However, compostul bun can mean the good compost, where bun directly describes the noun inside a noun phrase.

This is an important distinction:

• compostul bun = the good compost
• compostul este bun = the compost is good

In compostul bun, bun is directly attached to the noun as an adjective inside the noun phrase.

In compostul este bun, bun is a predicate adjective, linked to the noun by este.

English makes the same distinction:

• the good compost
• the compost is good

The plural would be:

• Composturile sunt bune = The composts are good / The types of compost are good

Breakdown:

• composturile = the composts
• sunt = are
• bune = plural form of good for neuter/feminine plural

Because compost is neuter, its plural behaves like feminine for adjective agreement.

Yes, it is grammatically natural.

Whether it sounds natural in real life depends on context, just as in English. A Romanian speaker might say it when talking about gardening, soil quality, or waste recycling.

In everyday speech, many speakers would probably say:

• Compostul e bun

That is the same sentence in a more conversational style.