Learn Dutch: Het gras waarvan we het zaad verzamelen, is heel zeldzaam. - The grass whose seed we collect is very rare.

Because gras is a thing, not a person. In Dutch, words like wiens or van wie are strictly for people. When you want to say "whose" or "of which" for an inanimate object or concept, you must use waarvan.

Why do we say waarvan we het zaad... instead of just waarvan we zaad...?

In English, "whose" replaces "the" (we say "whose seed"). In Dutch, waarvan acts more like "of which", so the noun that follows still needs its article. You have to include het because you are literally saying "of which we collect the seed".

Why is the verb verzamelen at the end of the middle part?

The part of the sentence introduced by waarvan is a relative clause, which follows the same word order rules as a subordinate clause. This means the conjugated verb (verzamelen) must be pushed to the very end of that clause.

Why does is come immediately after the comma?

The entire first part of the sentence, Het gras waarvan we het zaad verzamelen, functions as a single long subject. The comma helps separate this subject from the main verb (is), which naturally follows it to complete the sentence.