Sólblómin blómstra seinna en túlípanarnir í garðinum okkar.

Because Icelandic usually puts the definite article on the end of the noun.

• sólblóm = sunflowers
• sólblómin = the sunflowers
• túlípanar = tulips
• túlípanarnir = the tulips

So where English uses a separate word like the, Icelandic often uses a suffix instead. In this sentence, the speaker is talking about specific flowers, not flowers in general.

The dictionary forms are:

• sólblóm = sunflower / sunflowers as a basic noun form
• túlípani = tulip

In the sentence, both are plural and definite:

• sólblómin = nominative plural definite of sólblóm
• túlípanarnir = nominative plural definite of túlípani

A learner often needs to “peel off” the endings to find the base form.

Because the subject is plural.

Here, sólblómin is they in meaning, so the verb takes the 3rd person plural form:

• hann blómstrar = he/it blooms
• þau blómstra = they bloom

So Sólblómin blómstra means The sunflowers bloom.

Yes. They are closely related.

• blóm = flower
• að blómstra = to bloom, to blossom

So the sentence contains both a flower noun and a verb built from the same idea. That is why sólblómin blómstra may look a little repetitive to an English speaker, but it is completely natural.

Seinna means later.

It is the comparative form of seint (late), used adverbially here:

• seint = late
• seinna = later

So the sentence is comparing blooming times: the sunflowers bloom later than the tulips.

Here, en means than.

After a comparative word like seinna (later), Icelandic uses en:

• seinna en = later than

This can confuse learners because en can also mean but in other sentences. In this sentence, though, it clearly means than because it follows a comparative.

Because í takes different cases depending on meaning:

• í
  • accusative = movement into
• í
  • dative = location in

Here the meaning is location, not movement, so Icelandic uses the dative:

• í garðinum = in the garden

Compare:

• Ég er í garðinum. = I am in the garden.
• Ég fer í garðinn. = I go into the garden.

That is a very common Icelandic pattern. Possessive pronouns often come after the noun, especially when the noun is definite:

• garðinum okkar = our garden
• literally something like the garden ours

This sounds unusual to an English speaker, but it is normal Icelandic word order.

Because Icelandic commonly uses both the definite form and the possessive together.

So garðinum okkar is the natural way to say our garden in this kind of sentence. English usually does not say the our garden, but Icelandic often combines definiteness and possession this way.

The sentence follows a very normal Icelandic main-clause pattern:

• Sólblómin = subject
• blómstra = finite verb
• seinna = adverb/comparative
• en túlípanarnir í garðinum okkar = comparison phrase

So the structure is basically:

Subject + Verb + Later + than-phrase

This also fits the Icelandic verb-second tendency: in a main clause, the finite verb usually comes very early, often in second position.

Grammatically, it most directly attaches to túlípanarnir, so the clearest reading is:

the tulips in our garden

So the sentence most naturally means that the sunflowers bloom later than those tulips. In real context, of course, a listener may understand that the speaker is talking about the flowers in their garden generally, but the phrase is placed right after túlípanarnir, so it is most closely linked to that noun.