Vi sætter parasollen op, når solen bliver for stærk.

Sætter ... op is the verb at sætte op, which means to put up, to set up, or to erect.

In Danish, verbs like this often work a bit like English phrasal verbs. In a main clause, the finite verb comes early, while the particle can appear later:

• Vi sætter parasollen op. = We put the parasol up.

So sætter and op belong together in meaning, even though they are split in the sentence.

In Danish, the definite article is usually added to the end of the noun.

• en parasol = a parasol

• parasollen = the parasol

• en sol = a sun
• solen = the sun

So instead of using a separate word like English the, Danish often attaches it as an ending.

A small spelling detail: parasol becomes parasollen with double l in the definite singular form.

Når means when here. It is used for something that happens generally, repeatedly, or in the future.

So this sentence means something like:

• We put up the parasol when the sun gets too strong
• or whenever the sun gets too strong

That is why når fits well.

A useful contrast:

• når = when / whenever
• hvis = if
• da = usually when about a specific past event

Danish often uses the present tense for future meaning when the context is clear.

So:

• Vi sætter parasollen op, når solen bliver for stærk.

can refer to a regular habit or to something that will happen later.

This is very similar to English in sentences like:

• We’ll put up the parasol when the sun gets too strong.

Notice that English also often uses present tense in the when clause: when the sun gets too strong, not when the sun will get too strong.

Bliver literally means becomes or gets.

So:

• solen bliver for stærk = the sun becomes too strong / the sun gets too strong

In natural English, gets too strong is often the best translation here.

With weather or sunlight, stærk means strong in the sense of intense.

There is a small meaning difference:

• solen er for stærk = the sun is too strong
• solen bliver for stærk = the sun gets/becomes too strong

So bliver focuses on a change: the sun reaches the point where it is too strong.

That makes sense here, because the action of putting up the parasol happens when that change occurs.

Here for means too.

So:

• for stærk = too strong

This is a very common Danish use of for before adjectives and adverbs:

• for dyr = too expensive
• for varm = too hot
• for sent = too late

So in this sentence, for is not the English-style preposition for.

Because the adjective agrees with solen, which is a common-gender singular noun.

After verbs like er and bliver, Danish adjectives still show agreement:

• solen bliver stærk
• lyset bliver stærkt

Here:

• solen is common gender, so the adjective is stærk
• if the subject were a neuter noun, you would often get -t

So stærk is the correct form with solen.

If the subordinate clause comes first, the main clause changes word order because Danish is a V2 language.

So you can also say:

• Når solen bliver for stærk, sætter vi parasollen op.

Notice the change:

• Vi sætter parasollen op ...
• Når solen bliver for stærk, sætter vi parasollen op.

After the fronted når clause, the verb sætter comes before the subject vi in the main clause.

You will often see a comma before a subordinate clause in Danish, as in:

• Vi sætter parasollen op, når solen bliver for stærk.

That comma marks the start of the når clause.

In modern Danish, you may also see writing without that comma, depending on comma style:

• Vi sætter parasollen op når solen bliver for stærk.

So the comma is very common and very useful, but you may encounter both versions.

Yes. Very naturally.

Because the sentence uses present tense and når, it can describe a general routine:

• We put up the parasol whenever the sun gets too strong.

So depending on context, it can mean:

• a habit
• a general rule
• or a future action in a specific situation

That flexibility is very normal in Danish.