Learn Hardcore German: Wenn das Wetter zu heiß wird, stelle ich die Muscheln nicht in die Sonne. - When the weather becomes too hot, I do not put the shells in the sun.

In German subordinate clauses introduced by a subordinating conjunction like wenn, the finite verb moves to the very end. Here wird (from werden) follows all other elements in the wenn-clause.

Why does the main clause begin with stelle instead of ich stelle?

When a sentence (or clause) starts with anything other than the subject—in this case the wenn-clause—the following main clause uses inversion: the verb takes first position and the subject follows. That’s why you get stelle ich rather than ich stelle.

What is the function of zu in zu heiß?

zu here means too, intensifying the adjective. zu heiß translates to too hot, indicating an excessive degree.

Why doesn’t the adjective heiß take an ending after zu (i.e. why not zu heiße)?

When you use zu directly before an adjective to mean too + adjective, the adjective remains uninflected. So it’s always zu heiß, zu kalt, zu laut, etc.

Why is Muscheln preceded by die, and what case is it?

Muscheln is the plural of die Muschel (the shell). It’s the direct object of stelle, so it’s in the accusative plural. The definite article for accusative plural is die, giving die Muscheln.

Why is in die Sonne in the accusative case?

German prepositions can trigger different cases depending on motion vs. location. in + accusative indicates movement into something. Here you’re placing the shells into (toward) the sun’s rays, so die Sonne is accusative.

Why is nicht placed before in die Sonne rather than at the very end?

Nicht normally goes directly before the phrase or element it negates. Placing it before in die Sonne clearly negates the action “placing into the sun.” Putting nicht at the very end could make the sentence ambiguous, as if you did everything except that last phrase.

What’s the difference between using stelle, lege or setze here?

German has several verbs for “to put”:

stellen implies standing something upright.
legen implies laying something flat.
setzen usually means “to seat” or “set” something more animate.
With shells you could say lege ich die Muscheln in die Sonne if you think of them lying flat. stelle works if you imagine arranging them upright or simply “placing” them.

Can I use falls instead of wenn?

Yes. Both mean if, but nuance differs slightly:

wenn is neutral and common for real conditions.
falls often sounds more hypothetical or cautious.
Falls das Wetter zu heiß wird… is grammatically correct, with a subtly more “just in case” tone.

Why is there an article before Sonne when English often says in sunshine without “the”?

In German you normally use an article with concrete nouns. Here Sonne is feminine, so its accusative article is die. English sometimes treats “sunshine” as an uncountable concept and drops “the,” but German prefers in die Sonne to mean “into the sun / sun’s rays.”