Í júlí blómstra sum sólblóm alveg við gluggann.

Because Icelandic main clauses usually follow the verb-second rule.

In this sentence, Í júlí takes the first position. Once that happens, the finite verb blómstra must come next, and the subject sum sólblóm comes after it.

So the structure is:

• Í júlí = first element
• blómstra = finite verb in second position
• sum sólblóm = subject

A more basic subject-first version would be:

• Sum sólblóm blómstra alveg við gluggann í júlí.

Both are possible, but the given sentence puts focus first on Í júlí.

Because sum has to agree with sólblóm in gender and number.

Sólblóm is a neuter noun, and here it is plural. The correct form of sumur/sum/sumt for neuter plural is sum.

Compare:

• sumir = masculine plural
• sumar = feminine plural
• sum = neuter plural

So:

• sum sólblóm = some sunflowers

That is very common with Icelandic neuter nouns: the nominative singular and nominative plural are often identical.

So sólblóm can mean either:

• a sunflower
• sunflowers

You know it is plural here because of the words around it:

• sum = some, which points to plural
• blómstra = a plural verb form here

So the grammar around the noun tells you the number.

Here blómstra is the present tense plural form, matching the plural subject sum sólblóm.

With this verb, the form blómstra is also the dictionary form / infinitive, so learners often notice that it looks familiar. That is normal.

Very roughly:

• ég blómstra = I bloom
• þú blómstrar = you bloom
• hann/hún/það blómstrar = he/she/it blooms
• þeir/þær/þau blómstra = they bloom

Since the subject is plural, blómstra is the right form.

It is in the nominative, because it is the subject of the sentence.

The subject is the thing doing the action of blooming, so Icelandic puts it in the nominative:

• sum sólblóm = nominative plural neuter

That nominative form is also why the agreeing word is sum.

Here alveg is acting as an intensifier. It strengthens við gluggann.

So við gluggann means:

• by the window
• next to the window

And alveg við gluggann means something like:

• right by the window
• right next to the window
• directly by the window

So alveg does not mean completely in a literal sense here. It gives extra emphasis to the location.

Because gluggann is the definite form, meaning the window.

Icelandic usually adds the definite article as a suffix to the noun instead of using a separate word like English the.

So:

• gluggi = window
• gluggann = the window in this case/form

The ending -ann here shows both:

• definiteness
• the correct case form

Gluggann is accusative singular definite.

The reason is that the preposition við takes the accusative. So after við, you use the accusative form of gluggi:

• gluggi = basic form
• gluggann = accusative singular definite

So:

• við gluggann = by the window

This is a good example of how Icelandic prepositions often control the case of the noun that follows them.

Because í is the normal preposition used with months when Icelandic means in a certain month.

So Icelandic says:

• í júlí = in July
• í ágúst = in August
• í september = in September

This is simply the standard pattern for months and many other time expressions.

Also, júlí does not visibly change form here, so even if you are looking for a special ending, you will not see one.

Yes, but not freely. Icelandic word order is flexible, yet the finite verb in a main clause still normally stays in second position.

So these are fine:

• Í júlí blómstra sum sólblóm alveg við gluggann.
• Sum sólblóm blómstra alveg við gluggann í júlí.

But this is not normal main-clause word order:

• Í júlí sum sólblóm blómstra alveg við gluggann.

The reason is that after Í júlí in first position, the verb should come next.

Because sum sólblóm is an indefinite noun phrase: some sunflowers.

In Icelandic, if a noun phrase is indefinite, you usually do not add the definite article. And since sum already means some, the phrase is clearly indefinite.

So:

• sum sólblóm = some sunflowers
• not the sunflowers

That is why sólblóm appears without a definite ending here, while gluggann does have one.