Learn Dutch: Wij kopen de bloemetjes, tenzij je er drie grote wilt. - We are buying the little flowers, unless you want three big ones.

The word er here is the quantitative er, acting as a pronoun for the noun we just mentioned (bloemetjes). When you combine it with a number (drie) and an adjective (grote), the adjective stands in for the noun. In English, we use the word "ones" (three big ones), but Dutch just leaves the adjective hanging: er drie grote (literally "three big of them").

Why does grote get an -e ending if there is no noun right after it?

Even though the noun is omitted, the adjective still has to match the noun it represents! Because it refers back to bloemetjes, which is plural, the adjective gets the standard -e ending for plural nouns. When an adjective stands alone like this with er, it follows the exact same spelling rules as if the noun were still written right next to it.

Why is the verb wilt pushed to the very end of the sentence?

The word tenzij (unless) is a subordinating conjunction. This means it introduces a dependent clause, which forces the conjugated verb (wilt) all the way to the end of that clause.

The sentence mentions bloemetjes (little flowers) but then says drie grote (three big ones). How does that work?