Mein Bruder will den Garten mit Kompost düngen, statt teuren Dünger zu kaufen.

Because düngen takes a direct object in the accusative case.

• der Garten = nominative, the subject form
• den Garten = accusative, the direct object form

In this sentence, Mein Bruder is the subject, and den Garten is the thing being fertilized.

So:

• Mein Bruder = the person doing the action
• den Garten = what receives the action

Mit always takes the dative case, but Kompost here is being used as an uncountable material noun, similar to with water, with soil, or with compost in English.

So:

• mit Kompost = with compost, using compost as a substance

You could say mit dem Kompost if you mean a specific compost, for example the compost we made last year. But in this sentence, it means compost in a general sense, so no article is needed.

They are closely related:

• düngen = to fertilize
• der Dünger = fertilizer

So düngen is the verb, and Dünger is the noun made from the same idea.

This is similar to English pairs like:

• to drive / the driver
• to teach / the teacher

In the sentence:

• den Garten mit Kompost düngen = to fertilize the garden with compost
• teuren Dünger kaufen = to buy expensive fertilizer

Because will is a modal verb.

In German main clauses, the conjugated verb goes in position 2, and when a modal verb is used, the other verb stays in the infinitive at the end of the clause.

So:

• Mein Bruder will den Garten mit Kompost düngen.

Breakdown:

• Mein Bruder = subject
• will = conjugated modal verb in position 2
• den Garten mit Kompost düngen = rest of the clause, with düngen at the end

This is a very common German pattern.

Because statt introduces a zu-infinitive clause.

In German, infinitive clauses with words like:

• um
• ohne
• statt / anstatt

are normally separated by a comma.

So:

• ..., statt teuren Dünger zu kaufen.

That comma helps show that the sentence now moves into a new infinitive construction: instead of buying expensive fertilizer.

Because after statt, German often uses an infinitive clause with zu.

So:

• statt teuren Dünger zu kaufen = instead of buying expensive fertilizer

This is a standard structure:

• statt + infinitive with zu

Examples:

• statt zu arbeiten = instead of working
• statt nach Hause zu gehen = instead of going home
• statt teuren Dünger zu kaufen = instead of buying expensive fertilizer

Because Dünger is masculine and it is the direct object of kaufen, so it is in the accusative case.

Also, there is no article before it, so the adjective takes a strong ending.

For masculine:

• nominative: teurer Dünger
• accusative: teuren Dünger

Here we need the accusative because he would be buying the fertilizer:

• teuren Dünger kaufen

German often leaves out the article when speaking in a general or nonspecific way, especially with materials, products, or abstract categories.

So teuren Dünger means something like:

• expensive fertilizer
• expensive kinds of fertilizer

If you wanted to refer to one specific fertilizer, you could say:

• einen teuren Dünger kaufen = buy an expensive fertilizer

Both are possible, but the version without the article sounds more general.

Because it belongs to the zu-infinitive clause introduced by statt.

In German infinitive clauses, the infinitive usually goes at the end:

• statt teuren Dünger zu kaufen

The same pattern appears in sentences like:

• um Geld zu sparen
• ohne etwas zu sagen
• statt nachzudenken

So kaufen goes last because it is the infinitive verb of that subordinate infinitive construction.

Yes. Statt and anstatt are both possible here.

So you could also say:

• Mein Bruder will den Garten mit Kompost düngen, anstatt teuren Dünger zu kaufen.

That means the same thing.

In everyday German, statt is often a bit shorter and more common in speech, but both are standard.

Here it functions as part of a structure introducing an infinitive clause: statt ... zu + infinitive.

So in this sentence, it is best understood as introducing the idea instead of doing something.

Compare:

• statt teuren Dünger zu kaufen = instead of buying expensive fertilizer

But statt can also behave more like a preposition in other contexts, for example:

• statt teurem Dünger = instead of expensive fertilizer

So German allows both patterns:

• statt + noun phrase
• statt + zu-infinitive clause

Yes. You could rephrase it in several ways.

For example:

• Mein Bruder will den Garten mit Kompost düngen und keinen teuren Dünger kaufen.
• Mein Bruder will den Garten mit Kompost düngen, anstatt teuren Dünger zu kaufen.

The original version is concise and natural because it expresses the contrast very neatly: he wants to do one thing instead of another.

Not in the same meaning.

• düngen = to fertilize
• kompostieren = to compost, meaning to turn waste into compost

So:

• den Garten mit Kompost düngen = to fertilize the garden with compost
• Abfälle kompostieren = to compost waste

They are related in topic, but they are not interchangeable verbs.

The sentence has two main parts:

1. Main clause

   • Mein Bruder will den Garten mit Kompost düngen
   • subject + modal verb + object + phrase + infinitive

2. Infinitive clause with statt

   • statt teuren Dünger zu kaufen
   • instead of buying expensive fertilizer

So the overall pattern is:

• [main clause] + , statt + [object] + zu + infinitive

This is a very useful pattern to learn for expressing instead of doing X in German.