以下两种表达都可以，前者是with 复合结构；后者是独立主格结构。都是作原因状语。

The street is beautiful, with trees and flowers growing well along it.

The street is beautiful, trees and flowers growing well along it.

副词 well 和介词短语 along it， 可以有两种分析：

1. 分别修饰 growing，一个是方式状语，一个是地点状语。

2. well 修饰 along，说明其程度。意思是：沿街两侧全都是树木花卉。well 修饰介词的情况比较常见。又如：

well worth reading（很值得一读）

well above my head （远远高于我头顶）