Obierki są w kompostowniku.

Because obierki usually means peelings / scraps from peeling, which are naturally thought of as multiple bits, not one single item.

• Singular: obierka = a peel, a peeling
• Plural: obierki = peelings

In everyday Polish, obierki is very commonly used in the plural, much like English peelings.

Here obierki is in the nominative plural, because it is the subject of the sentence.

The verb są means are, so the structure is:

• obierki = the peelings
• są = are
• w kompostowniku = in the composter / compost bin

So obierki is the thing that is somewhere, which makes it the subject.

A useful extra note: for nouns like this, the nominative plural and accusative plural can look the same, so context matters.

Są is the 3rd person plural form of być (to be) in the present tense.

Because obierki is plural, Polish uses the plural verb:

• jest = is
• są = are

So:

• Obierka jest... = The peel is...
• Obierki są... = The peelings are...

Unlike English, Polish often drops subject pronouns like they, but the verb still changes to show number and person.

In a full normal sentence, są is standard and expected.

However, in very informal styles such as labels, notes, instructions, or headlines, Polish sometimes drops forms of to be:

• Obierki w kompostowniku = a shortened, note-like version

But in ordinary complete speech and writing, Obierki są w kompostowniku is the normal form.

Because after w meaning in, when it shows location, Polish uses the locative case.

The dictionary form is:

• kompostownik = composter / compost bin

But after w for location, it changes to:

• w kompostowniku = in the composter

So:

• w + locative = in / at / inside, when something is located somewhere

It is the locative singular of kompostownik.

Here is the pattern:

• nominative: kompostownik
• locative: w kompostowniku

Many masculine nouns in Polish take -u in the locative singular, although this is something learners mostly absorb over time rather than fully predict in every case.

The important point here is:

• w
  • location → usually locative
• therefore kompostownik becomes kompostowniku

Not always. It depends on the meaning.

With w, there are two common possibilities:

• location → locative
• motion into → accusative

Examples:

• Jest w domu. = He/She is in the house.
  → location, so locative
• Idzie w las. = He/She is going into the forest.
  → movement, so accusative

In Obierki są w kompostowniku, the peelings are already located there, so Polish uses the locative.

Because Polish does not have articles like English a and the.

So obierki can mean:

• peelings
• the peelings

And w kompostowniku can mean:

• in a composter
• in the composter

Context tells you which meaning is intended.

This is very normal in Polish, and learners get used to relying more on context than on articles.

No, Polish word order is fairly flexible.

Obierki są w kompostowniku is a neutral, straightforward order.

But you could also say:

• W kompostowniku są obierki.

This puts more focus on the location, as if answering Where are the peelings?

So both are grammatical, but the emphasis changes.

Kompostownik means a composter, compost bin, or compost container/place where organic waste is put to decompose.

It is different from kompost, which means compost itself, the material.

So:

• kompost = compost
• kompostownik = composter / compost bin

That is why w kompostowniku means in the compost bin / composter, not in the compost.

A simple approximate pronunciation is:

oh-BYER-kee sown v kom-po-stow-NEE-koo

A few helpful points:

• bie in obierki sounds roughly like byeh
• ą in są is a nasal vowel; before w, in normal speech it often sounds close to om or on
• w is pronounced like English v
• stress in Polish usually falls on the second-to-last syllable, so:
  • o-BIER-ki
  • kom-po-stow-NI-ku

Yes, depending on what you mean.

For example:

• resztki = leftovers, scraps
• odpady organiczne = organic waste
• skórki = peels/skins, often specifically skins like potato peels or fruit peels

These are not always exact synonyms:

• obierki strongly suggests peelings from vegetables or fruit
• resztki is broader
• odpady organiczne sounds more formal or general

So obierki is a very natural choice if you mean peelings specifically.