Grasið í garðinum er grænt eftir rigninguna.

to be

Breakdown of Grasið í garðinum er grænt eftir rigninguna.

• í: in
• eftir: after
• garðurinn: the garden

Questions & Answers about Grasið í garðinum er grænt eftir rigninguna.

Why does gras become grasið here? What does the ending -ið mean?

The base noun is gras (neuter, “grass”).
When you add the definite article “the” in Icelandic, it becomes a suffix:

• gras = grass
• grasið = the grass

For most neuter nouns, the definite singular nominative/accusative ending is -ið. So grasið literally means “the grass.”

In English I’d say “Grass is green.” Why is it “the grass” (grasið) here? Can I say Gras er grænt instead?

Yes, you can say Gras er grænt to state a general fact, “Grass is green.”

In your sentence, though, Grasið í garðinum points to a specific patch of grass:

• Gras er grænt = Grass (in general) is green
• Grasið í garðinum er grænt = The grass in the garden is green (this particular garden)

Because you identify a particular garden (í garðinum), Icelandic very naturally makes the grass definite too: grasið.

What case is grasið in, and how can I recognize it?

Grasið is in the nominative singular because it is the subject of the sentence.
Clues: