Learn Hardcore Finnish: Kastelen kasvin kahdesti viikossa, jotta se pysyy terveenä. - I water the plant twice a week so that it stays healthy.

kasvin is the genitive singular form, which in Finnish also serves as the accusative for a complete, bounded action. You use the genitive/accusative when the action affects the whole object as a single unit (telic action)—here, each watering is a finished event applied to the entire plant. The partitive kasvia would suggest an incomplete or ongoing action (atelic), e.g. “I’m watering some of the plant” or “I water it in general,” which isn’t the nuance intended.

How is kahdesti viikossa constructed, and what exactly does it mean?

kahdesti is an adverb meaning “twice,” formed by adding -sti to the numeral kaksi (two). viikossa is the inessive case of viikko (“week”), literally “in a week.” Together, kahdesti viikossa translates as “twice a week.” Finnish commonly uses the inessive to indicate frequency per time unit (e.g. kuukaudessa = “per month,” päivässä = “per day”).

Why is jotta used here instead of että, and what’s the difference?

jotta introduces a purpose clause (“so that,” “in order that”), expressing the goal of the main action. In this sentence, it tells us why you water the plant: “so that it stays healthy.” By contrast, että is a neutral conjunction meaning “that” and is used for reporting statements or thoughts (e.g. “I know that…”). You choose jotta whenever you want to convey purpose.

Why is terveenä in the form ending with -nä, and what case is that?

terveenä is the essive case of the adjective terve (“healthy”). After verbs of state or change like pysyä (“stay”), Finnish uses the essive (-na/-nä) to express the resulting or continuing state. So pysyy terveenä literally means “stays in the state of being healthy.”

What verb type is kastella, and how do you form the 1st person singular present kastelen?

kastella is a type 4 verb (verbs ending in -tella/-tellä). To conjugate in the 1st person singular present:

Remove -tella to get the stem kastele-.
Add -n, yielding kastelen.
Note that the double ll in the infinitive reduces to a single l in the stem.

Why does Finnish use se to refer to the plant, instead of separate words for “he,” “she,” or “it”?

Finnish has one third-person pronoun, se, for all genders and for “it.” There is no gender distinction, so se comfortably covers “he,” “she,” or “it” depending on context. Here, se points back to kasvi (“the plant,” which is gender-neutral).

Is the word order flexible if I want to emphasize something else in the sentence?

Yes, Finnish word order is relatively free for emphasis. You could say, for example:
– Kahdesti viikossa kastelen kasvin, jotta se pysyy terveenä. (Emphasizing frequency)
– Jotta se pysyy terveenä, kastelen kasvin kahdesti viikossa. (Emphasizing purpose)
The default is Kastelen kasvin kahdesti viikossa, jotta se pysyy terveenä, which places the time expression right after the verb phrase.