Where does “kasvettuminen” come from?

kasvettuminen (Finnish) comes from Finnish kasvettua, from Finnish -ttua, from Finnish -ttää, from Proto-Finnic -ttadak, from Proto-Uralic -kta-.

Ancestry of “kasvettuminen”, step by step

Step	Language	Word	Meaning
1	Finnish	kasvettua	to grow together or shut
2	Finnish	-ttua	Forms inchoative or passive intransitive verbs...
3	Finnish	-ttää	Front vowel variant of -ttaa
4	Proto-Finnic	-ttadak	Creates causative verbs from regular verbs,...
5	Proto-Uralic	-kta-	—