Learn Hardcore Norwegian: Jeg lukker gardinen når solen blir for sterk. - I close the curtain when the sun becomes too strong.

Norwegian often uses the definite form for specific, identifiable things. The sun is unique, so it’s almost always solen/sola. The curtain is also a specific one in the room, so gardinen is natural. Using the indefinite (en gardin) would sound like “a curtain (any curtain),” which isn’t what you mean here.

Can I say sola instead of solen? What about gardina vs gardinen?

Yes. In Bokmål, many feminine nouns can be treated as feminine or masculine:

sol is commonly feminine in usage: sola (very common) or solen (also correct, a bit more formal).
gardin is usually masculine (en gardin – gardinen), but some speakers use feminine forms: ei gardin – gardina. Pick one style and be consistent within a text.

Why use blir (“becomes”) and not er (“is”)?

blir emphasizes a change: at the point when the sun gets too strong. er describes a state.

Jeg lukker gardinen når solen blir for sterk. = I close it when it becomes too strong.
Jeg lukker gardinen når solen er for sterk. = Whenever it is too strong, I close it (state-based rule).

Is lukker gardinen idiomatic for curtains?

It’s understandable, but Norwegians often prefer:

Jeg trekker for gardinene / drar for gardinene. (I draw the curtains.)
For a roller blind: Jeg ruller ned rullegardinen. Avoid stenger gardinen; stenge is for doors/shops.

What’s the difference between når, da, and om?

når = when (present/future or repeated/habitual): Jeg lukker gardinen når solen blir for sterk.
da = when (one specific time in the past): Jeg lukket gardinen da solen ble for sterk i går.
om = if/whether: Jeg lukker gardinen om solen blir for sterk. (conditional “if,” not “whenever”) Note: hvis also means “if.”

Why is it når solen blir..., not når blir solen...?

Because når introduces a subordinate clause, which uses subject–verb order (SV): solen (S) + blir (V). If that clause comes first, the following main clause shows V2:

Når solen blir for sterk, lukker jeg gardinen.

Do I need a comma before når here?

No. Modern Norwegian typically has no comma before a subordinate clause that follows the main clause: Jeg lukker gardinen når solen blir for sterk. If the subordinate clause comes first, put a comma after it:

Når solen blir for sterk, lukker jeg gardinen. (Some writers use a “start comma,” but the no-comma style is standard.)

Where would the negation ikke go?

Main clause negation: Jeg lukker ikke gardinen når solen blir for sterk.
If the time clause comes first: Når solen blir for sterk, lukker jeg ikke gardinen.
Negating the time clause (different meaning): Jeg lukker gardinen når solen ikke blir for sterk.

Does the adjective agree with the subject? Why sterk, not sterkt/sterke?

Yes. After bli, the adjective agrees with the subject:

solen/sola (common gender, singular) → sterk.
Neuter subject: sollyset blir for sterkt.
Plural subject: blir for sterke.

What does for mean here? Is it “for/because”?

Here for is an adverb meaning “too”: for sterk = “too strong.” It’s not the conjunction for (“because”). Related options:

altfor sterk = far too strong
veldig sterk = very strong
for mye sol = too much sun

Is present tense correct even though this refers to future situations too?

Yes. Norwegian uses the present in time clauses for future reference and for habits:

Jeg lukker gardinen når solen blir for sterk. You can use skal for a specific plan: Jeg skal lukke gardinen når solen blir for sterk (i ettermiddag). Don’t say når solen vil bli.

Should it be singular gardinen or plural gardinene?

Both are possible, depending on what you have:

Two side curtains: Jeg trekker for gardinene. (plural definite is common)
One roller blind: Jeg ruller ned rullegardinen. Singular in your sentence is fine if you picture a single covering.

Do I need a possessive, like gardinen min?

Usually not. Norwegian often omits possessives when ownership is obvious or context makes the item specific. Jeg lukker gardinen naturally refers to the curtain in the room. Use a possessive only for emphasis or contrast: Jeg lukker gardinen min, ikke din.

Could I say mens instead of når?

No. mens = “while” (two things happen at the same time): Jeg leser mens solen skinner. Your sentence expresses a trigger/condition, so når is correct.

Are there useful synonyms for window coverings and matching verbs?

gardin/gardiner = curtains → trekke/drar for, trekke/drar fra
rullegardin = roller blind → rulle ned / rulle opp
persienner = venetian blinds → lukke / åpne persiennene (also vinkle lamellene for the slats)
forheng = curtain/hanging (often doorway/shower)

Any quick pronunciation tips for these words?

gardinen: in many dialects, rd merges to a single retroflex sound (a “thick d”): roughly “ga-dinen.”
solen: the o is like English “oo” in “food”: “SOO-len.”
blir: “bleer” with a long i.
for: short “fohr.”

How do I say the opposite (open the curtains)?

Jeg trekker fra gardinene / drar fra gardinene.
For a roller blind: Jeg ruller opp rullegardinen. You can also say Jeg åpner gardinene, but trekker/drar fra is the most idiomatic.