Heather was recognised by the ancient Celts as a great cleansing agent; as a very effective means of breaking up blockages found in the body.
Brooms were most popularly made by the Celts with heather - symbolic of clearing, cleansing and manifesting purity. These associations with purity more than likely gave rise to Heather being made a symbol of promise and good luck in the Scottish Highlands.
Heather is symbolically associated with purity, refinement, luck, beauty, romance, protection, cleansing and attraction. [Source: What's Your Sign]