Am Abend geht meine Schwester nicht in den Garten, weil dort viele Mücken sind.

Am Abend is a common time expression meaning in the evening.

• am = contraction of an dem
• With parts of the day like Morgen, Abend, etc., German often uses am:
  • am Morgen
  • am Abend
  • am Nachmittag

Putting Am Abend first sets the time right away. German often moves time expressions to the front of the sentence.

This is because German main clauses follow the verb-second rule.

The conjugated verb must be in the second position, not necessarily the second word.

So in:

Am Abend geht meine Schwester nicht in den Garten

the first position is the whole phrase Am Abend, and the second position is geht.

If you put the subject first, you would get:

Meine Schwester geht am Abend nicht in den Garten.

Both are correct.

Because meine Schwester is the subject of the sentence, so it is in the nominative case.

• meine Schwester = nominative
• meiner Schwester = usually dative or genitive, depending on context

Even though the subject comes after the verb here, it is still the subject.

Because this sentence expresses movement toward the garden, not location inside it.

German uses different cases after some prepositions depending on whether the meaning is:

• motion/direction → accusative
• location → dative

So:

• in den Garten gehen = to go into the garden
• im Garten sein = to be in the garden

Here, geht ... in den Garten shows direction, so den Garten is accusative.

The position of nicht depends on what is being negated.

In this sentence, nicht negates the idea of going into the garden:

geht meine Schwester nicht in den Garten

This means she does not go into the garden.

A useful rule:

• nicht often comes before the part it directly negates
• but it can also appear later in the sentence depending on structure

Here, putting nicht before in den Garten is very natural.

Weil means because and introduces a reason.

So the second part gives the reason for the first:

• first idea: she does not go into the garden
• reason: there are many mosquitoes there

Weil introduces a subordinate clause, which changes the word order.

Because after weil, German uses subordinate clause word order, where the conjugated verb usually goes to the end.

So:

• Main clause: Dort sind viele Mücken.
• After weil: weil dort viele Mücken sind

This is one of the most important word-order patterns in German.

Dort means there.

It refers to the place just mentioned: the garden.

So weil dort viele Mücken sind means literally something like:

because many mosquitoes are there

German often uses dort or da to refer back to a place already mentioned.

Both can mean there, and in many situations they are interchangeable.

Very roughly:

• da is often a bit more common and conversational
• dort can sound a little more specific or slightly more formal

In this sentence, dort works very naturally because it clearly points to the garden.

You could also say:

..., weil da viele Mücken sind.

That would still be correct.

Because viele is a quantifier meaning many, and it can be used directly with a plural noun.

So:

• viele Mücken = many mosquitoes

You do not need an article here.

Compare:

• viele Mücken = many mosquitoes
• die Mücken = the mosquitoes

German can express this idea in more than one way.

This sentence uses:

weil dort viele Mücken sind = literally, because many mosquitoes are there

You could also say:

weil es dort viele Mücken gibt = because there are many mosquitoes there

Both are correct.

The version with sind is a little more direct and simple in structure.

They are very similar, and in many cases both can mean in the evening.

• Am Abend refers to the evening as a time period
• abends often has a more general or habitual sense, like in the evenings

Examples:

• Am Abend geht meine Schwester nicht in den Garten.
  = on that evening / in the evening

• Abends geht meine Schwester nicht in den Garten.
  = in the evenings / evenings, she does not go into the garden

So they overlap, but abends often sounds more routine or repeated.

German uses articles very regularly, often more regularly than English learners expect.

Here, in den Garten is the normal way to say into the garden. The article helps show:

• the noun’s gender
• the case
• whether it is definite

Because Garten is masculine and the phrase shows movement, it becomes:

• der Garten → nominative
• den Garten → accusative

So the article is doing important grammatical work.