This is the 5689th most frequent Korean word.
방치해
"Neglect" or "leave unattended."
방치하다 here conveys 'to neglect or leave unattended' referring to not maintaining the car.
그는 오래된 차를 방치해 두었어요.
He neglected to take care of his old car.
In this sentence, 방치하다 illustrates leaving something, like the flowers, without care resulting in their deteriorating.
방치해 둔 꽃들이 시들기 시작했어요.
The flowers that were left unattended have started to wilt.
The term 방치하다 emphasizes the inappropriateness of disregarding responsibility, especially towards children, in this context.