Breakdown of On boi się, żeby grzałka nie spaliła roślin.
on
he / it (m)
nie
no / not
roślina
plant
żeby
so that, in order to
Questions & Answers about On boi się, żeby grzałka nie spaliła roślin.
Why is there a nie in this sentence when the English translation says might burn rather than might not burn?
This is called pleonastic (or redundant) negation. After verbs of fearing like bać się, when you use żeby, Polish adds an extra nie that doesn't actually negate the meaning. He is afraid of the heater burning the plants, not of it failing to burn them.
Why is the verb spaliła in the past tense if he is worried about a future event?
The word żeby always requires the verb to be in the past tense form (specifically the L-participle), regardless of when the action takes place. So even though the fear is about the future, żeby forces the use of spaliła.
The verb spalić usually takes the accusative case, so why is the object roślin in the genitive case here?
This is the genitive of negation in action! Even though the nie here is redundant and doesn't change the logical meaning, grammatically it still acts like a normal nie. Whenever a verb that normally takes the accusative is preceded by nie, its direct object must change to the genitive case.
Could we express this same fear using że instead of żeby?