Possible Clues:

• Plant of rocks and walls
• Plant that grows among rocks and on walls
• Plant men round exhibition centre -- prevent parking outside
• Plant growing on rocks
• Among various pots, there's single empty container for plant
• Plant single councillor brought into bar
• Bloomer made by single councillor in bar
• Plant often found on rocks and walls
• Wall-growing plant
• Flower right for planting in pots, once developed