Questions & Answers about Rosení není zálivka.
Rosení is a noun meaning something like misting, spraying a fine mist, or in some contexts dew formation/condensation. In a gardening context, it usually means lightly spraying water onto leaves or the surface.
Grammatically, it is a verbal noun: it comes from a verb and names the action itself.
That ending is very common in Czech verbal nouns. Czech often forms an abstract noun from a verb to mean the act/process of doing something.
So rosení means the act of misting/dewing rather than a concrete object.
Also, nouns ending in -ní are usually neuter, which is why rosení is neuter.