yes, the students are right. we can find many examples of such collocations.
1.Other wetland flowers would open later in the year;
2.The flowers only open during bright weather.
3.bronze-streaked yellow flowers open up wide in the low shafts of February sunshine.
4.their flowers don't open so well when put in a shady position.
5.The flowers should open and be at their glorious, fragrant best for Christmas.
"come up" "open up" and "closed" is also be used.
On dNo, I, I'm lucky I like flowers, some are coming up.
the flowers remain closed, revealing their full beauty only in the sunshine.