Parsellhagen åpner i dag.

It could be either, depending on context.

Grammatically, parsellhagen is the definite singular form of parsellhage:

• parsellhage = allotment garden / community garden
• parsellhagen = the allotment garden

Because it is the first word in the sentence, it is capitalized anyway, so you cannot tell from this sentence alone whether it is:

• just the common noun the allotment garden, or
• a place name such as Parsellhagen

So context decides.

Because Norwegian very often combines nouns into one compound word.

Here you can think of it like this:

• parsell = plot
• hage = garden
• parsellhage = allotment garden / plot garden

Then the definite ending is added to the whole compound:

• parsellhage → parsellhagen

This is very normal in Norwegian. English often writes these as separate words, but Norwegian usually prefers one compound word.

Because Norwegian usually puts the definite article at the end of the noun instead of using a separate word before it.

So:

• hage = garden
• hagen = the garden

And with the compound:

• parsellhage = allotment garden
• parsellhagen = the allotment garden

That -en ending is doing the job that the does in English.

Åpner is the present tense of å åpne, which means to open.

So:

• å åpne = to open
• åpner = opens / is opening / will open

Norwegian present tense is used more broadly than English present simple, so the exact English translation depends on context.

It can match any of those in English, depending on the situation.

In Norwegian, the present tense often covers:

• a general present: opens
• something happening around now: is opening
• a scheduled or near-future event: will open

With i dag added, the sentence often sounds like a scheduled event or something happening later the same day, so English might translate it as:

• The allotment garden opens today
• The allotment garden is opening today
• The allotment garden will open today

All are possible depending on the wider context.

Because åpner is already the finite verb.

In English, you often need an extra verb in forms like is opening. In Norwegian, a simple present form is often enough:

• Parsellhagen åpner i dag.

There is no need for an extra verb here unless you are making a different kind of structure.

That is a very normal Norwegian word order.

A basic pattern is:

• subject + verb + time expression

So:

• Parsellhagen = subject
• åpner = verb
• i dag = time expression

You can also move i dag to the front:

• I dag åpner Parsellhagen.

That is also correct, but then Norwegian keeps the verb in second position. This is an important feature of Norwegian word order.

I dag is a time expression meaning today.

It is best learned as a fixed phrase. It does not need an article, and it can appear in different places in the sentence:

• Parsellhagen åpner i dag.
• I dag åpner Parsellhagen.

Both are natural.

No. Norwegian does not capitalize all nouns.

Unlike German, ordinary nouns in Norwegian are normally written with a small letter. In this sentence, Parsellhagen is capitalized because:

• it is the first word of the sentence, and/or
• it may be a proper name

So you should not assume that all Norwegian nouns are capitalized.

In this sentence, åpner is being used intransitively, meaning something like opens or becomes open.

Norwegian often uses the active form this way, just like English can:

• Butikken åpner klokka ni. = The shop opens at nine.

This does not necessarily focus on who performs the action. It just states that the place becomes open.

The letter å is a separate Norwegian vowel. It is usually pronounced somewhat like the vowel in British English law, but longer and clearer.

So åpner is roughly:

• OH-pner

Very roughly, the stress is on the first syllable.

Also remember that å can be:

• a letter, as in åpne
• the infinitive marker, as in å åpne = to open

Those are two different things, even though they look the same.