▲need 用作行为动词表“需要”时，need doing = need to be done，即使用主动形式表被动含义。如：
1. The room needs cleaning.=The room needs to be cleaned. 这房间需要打扫了。
2. Your hair needs cutting.=Your hair needs to be cut. 你的头发该理了。
这样用的 need 主语也可是“人”。如：
3. The old man needs looking after.=The old man needs to be looked after. 这位老人需要人照顾。
但是你的句子有所不同：The hedges needn't be trimmed this week.
句子中的 needn't 不是行为动词，而是情态动词（因为用作实义动词的 need 是不能直接在其后加否定词 not 的）。
比较下面三句：
The hedges needn't be trimmed this week.
The hedges don't need to be trimmed this week.
The hedges don't need trimming this week.
▲以下动词、动词词组也有类似的用法：
1. bear 忍受; 忍耐; 承受
He can't bear to be laughed at/bear beinglaughed at. 他禁不住拿他取笑。
2. want 要, 要求, 需要（某事物）
The plants want watering/ want to bewatered daily. 这些花草得天天浇水。
3. require 要求，需要
All cars require servicing regularly. 所有汽车都需要定期检修。
4. deserve 应得，值得
This film deserves watching. 这部电影值得看。
5. be worth 值得
The book is worth reading. 这本书值得一读。