Auf dem Kompost liegen alte Blätter und Gemüsereste, die später zu guter Erde werden.

Because this sentence describes a location, not movement.

With two-way prepositions like auf, German uses:

• dative for location: auf dem Kompost = on the compost
• accusative for movement toward somewhere: auf den Kompost = onto the compost

So here, the leaves and vegetable scraps are already there, just lying there, so German uses the dative: dem.

Liegen means to lie or to be lying. German often prefers a position verb where English would simply say to be.

So:

• Auf dem Kompost sind alte Blätter ... would be understandable, but less natural.
• Auf dem Kompost liegen alte Blätter ... sounds more vivid and idiomatic, because the things are physically lying there.

German commonly uses verbs like:

• liegen = lie / be lying
• stehen = stand / be standing
• sitzen = sit / be sitting

German main clauses follow the verb-second rule.

That means the finite verb must come in the second position, not necessarily after the subject.

Here the sentence begins with a prepositional phrase:

• Auf dem Kompost = position 1
• liegen = position 2
• alte Blätter und Gemüsereste = then the subject

So the structure is:

Auf dem Kompost | liegen | alte Blätter und Gemüsereste

If you started with the subject instead, you could also say:

Alte Blätter und Gemüsereste liegen auf dem Kompost.

Both are correct, but the original version puts emphasis on where they are.

Because Blätter is plural here, and there is no article before the adjective.

In German, adjective endings depend on:

• gender
• number
• case
• whether there is an article

Here:

• Blätter = plural
• it is part of the subject, so nominative
• there is no article

That gives the adjective ending -e:

• alte Blätter

The same pattern appears with:

• frische Tomaten
• reife Äpfel

Gemüsereste is a compound noun:

• Gemüse = vegetables
• Reste = remains / scraps / leftovers

So Gemüsereste means vegetable scraps or vegetable remains.

A few useful points:

• das Gemüse is usually treated as a collective noun in German.
• der Rest = the remainder / leftover
• plural: die Reste

Together: die Gemüsereste

German makes compounds very freely, so long nouns like this are very common.

The die is a relative pronoun, and it refers back to:

alte Blätter und Gemüsereste

Since that whole noun phrase is plural, the relative pronoun is also plural:

• die

So the relative clause means:

which later become good soil

In other words, the leaves and vegetable scraps are the things that turn into earth/soil.

Because in German, a relative clause is a type of subordinate clause, and subordinate clauses send the conjugated verb to the end.

So:

• main clause: Auf dem Kompost liegen ...
• relative clause: die später zu guter Erde werden

This is a very common pattern:

• der Mann, der dort steht
• das Buch, das ich lese
• die Dinge, die später nützlich werden

So the final werden is exactly what you should expect in a relative clause.

The pattern zu + dative + werden means to become into / to turn into something.

So:

• zu Erde werden = to become soil/earth
• zu guter Erde werden = to become good soil

This is a common structure:

• Wasser wird zu Eis. = Water turns to ice.
• Die Raupe wird zu einem Schmetterling. = The caterpillar turns into a butterfly.

So werden by itself means to become, but zu + dative tells you what something becomes.

Because zu takes the dative case.

The noun is die Erde, and in this phrase it is singular feminine in the dative, with no article. That gives:

• zu guter Erde

This is the adjective ending used after a preposition requiring dative when there is no article.

Compare:

• zu kaltem Wasser
• zu frischer Luft
• zu guter Erde

Not exactly. They overlap, but they are not always interchangeable.

• die Erde can mean earth, soil, or even the planet Earth
• der Boden usually means ground, floor, or soil in a more physical surface sense

In a compost context, gute Erde is very natural and often means good soil or rich earth.

So here Erde fits well because compost turns into fertile earth/soil.

No—German capitalizes all nouns, not just important ones.

So in this sentence, these are capitalized because they are nouns:

• Kompost
• Blätter
• Gemüsereste
• Erde

This is one of the most noticeable differences from English spelling.

Because the subject of the relative clause is plural:

alte Blätter und Gemüsereste

So the verb must also be plural:

• ich werde
• du wirst
• er/sie/es wird
• wir werden
• ihr werdet
• sie werden

Here it is sie werden, where sie would stand for they. The relative pronoun die is referring to a plural noun phrase, so the verb is werden.

Yes. A very normal alternative would be:

Alte Blätter und Gemüsereste liegen auf dem Kompost und werden später zu guter Erde.

That version is a bit more straightforward for learners because the subject comes first.

The original sentence, however, is elegant and natural because:

• it begins with the location
• it uses a relative clause to add extra information

So the original wording is not strange—it is just a slightly more advanced sentence structure.