Im Sommer verwelken die Blumen auf dem Balkon schnell.

Because German normally uses in + dative article with seasons:

• im Sommer = in dem Sommer
• im Winter
• im Frühling
• im Herbst

So in Sommer is not correct in standard German.

Here, im Sommer means in summer / during the summer.

Sommer is in the dative case because it comes after the preposition in in a time expression here.

• in can take different cases in different situations
• with expressions like im Sommer, it is dative

So:

• der Sommer → nominative
• dem Sommer → dative
• im Sommer = in dem Sommer

Because die Blumen is the subject of the sentence, and the subject is in the nominative case.

The verb is verwelken = to wilt / wither, so the flowers are the ones doing that action:

• die Blumen verwelken = the flowers wilt

Also, Blumen is plural, and the nominative plural definite article is die.

Here it is plural.

German die can mean:

• the for a feminine singular noun
• the for any plural noun

Since Blumen is the plural of Blume, die Blumen means the flowers.

Because auf is a two-way preposition.

Two-way prepositions use:

• dative for location: where something is
• accusative for direction/movement: where something is going

Here, the flowers are located on the balcony, not moving onto it, so German uses dative:

• auf dem Balkon = on the balcony

Compare:

• Die Blumen stehen auf dem Balkon. = The flowers are on the balcony.
• Ich stelle die Blumen auf den Balkon. = I put the flowers onto the balcony.

dem Balkon is dative singular.

The noun is:

• der Balkon = nominative
• dem Balkon = dative

It is dative because auf is being used for a fixed location here: on the balcony.

German often puts adverbs like schnell later in the sentence, especially after the subject and place expression.

The basic structure here is:

• Im Sommer = time
• verwelken = verb
• die Blumen = subject
• auf dem Balkon = place
• schnell = adverb

This word order sounds natural in German. English often puts quickly earlier or later depending on style, but German commonly allows it near the end.

Yes, German word order is flexible, but the finite verb in a main clause must stay in second position.

For example, all of these are possible:

• Im Sommer verwelken die Blumen auf dem Balkon schnell.
• Die Blumen verwelken im Sommer auf dem Balkon schnell.
• Auf dem Balkon verwelken die Blumen im Sommer schnell.

What changes is the emphasis, not the basic meaning.

The given sentence starts with Im Sommer, so it emphasizes the time.

Because in a German main clause, the conjugated verb must be in position 2.

Here, Im Sommer takes the first position as one complete unit. That means the verb must come next:

• Im Sommer | verwelken | die Blumen ...

Even though Im Sommer has two words, it counts as one sentence element.

verwelken is a normal, non-separable verb meaning to wilt or to wither.

In this sentence it is conjugated for third person plural because the subject is die Blumen:

• ich verwelke
• du verwelkst
• er/sie/es verwelkt
• wir verwelken
• ihr verwelkt
• sie verwelken

So:

• die Blumen verwelken = the flowers wilt

Because German, like English, often uses the present tense for general truths, habits, and repeated situations.

So verwelken here does not mean only right now. It can mean something like:

• Flowers on the balcony wilt quickly in summer
• a general fact or regular occurrence

This is very normal in German.

It mainly gives the location of the situation: the flowers are on the balcony when this happens.

In practice, it is understood as part of the whole idea:

• the flowers on the balcony wilt quickly in summer

So it is connected to the flowers, but grammatically it functions as a prepositional phrase of location in the sentence.

Because all nouns are capitalized in German.

Here the nouns are:

• Sommer
• Blumen
• Balkon

This is a basic rule in German spelling. Verbs like verwelken and adverbs like schnell are not capitalized unless they begin the sentence.

Yes, absolutely.

That version is also correct and may feel closer to English because die Blumen auf dem Balkon stays together as a noun phrase:

• Die Blumen auf dem Balkon = the flowers on the balcony
• verwelken = wilt
• im Sommer = in summer
• schnell = quickly

The original sentence is just choosing to emphasize Im Sommer first.