Bent is the rough grass that grows by the sea - it symbolises resilience - the abilty to bend without breaking
Broom is a plant associated with good luck -in Clare, Ireland it is called 'the May blossom' and was brought into the house on the 1st May to ensure a years good luck
The combination of the two is used in ballads such as 'Riddles Wisely Expounded' as a defence against possible danger from a stranger - particularly from 'The North Country' - (unknown territory)   
Jim Carroll