"Flowers bloom in the spring."
Translation:봄에는 꽃들이 펴.
It must be written as "봄에는 꽃들이 피어." Koreans never write '피(bloom) + 어' as '펴'. '펴' is only used for '펴(spread) + 어'. '펴' as 'bloom' is used only as an extremely informal spelling in order to show its oral transcription and not considered as an appropriate normal spelling.
- 피다: to bloom
- 펴다: to spread
The the existence of 펴다 keeps the ㅣ apart ㅓ in the 피어 as a disambiguation mechanism.
Regardless of the existence of 펴다, one can write 펴 for 피- + -어. Korean does not have such a mechanism.
피- + -어 can be contracted to 펴 and Koreans do write this way. It is neither informal nor inappropriate. You are confusing this with 사귀다 or 바뀌다.