Our ancestors have used LAVENDER to provide stress release, calm their burns, and as a pesticide. 

Similarly ROSEMARY wards of insects such as the common poultry mite. Rosemary also assists the memory, maybe not so essential for your hens, but a great benefit for us humans with all our hectic schedules.

 TEA TREE is both anti bacterial and ANTI VIRAL. Wormwood has benefits, hinted at in it's name. The listed benefits are just a few, there are more if you wish to search them up for each of these WONDERFUL woody aromatic plants.  It is well worth the time and effort to source plants providing these BENEFITS  for yourself and your animals. We can supply these plants.  

Another favourite plant of my hens is the Lucky Jade or Money Plant, Dollar Plant, Friendship Tree, Pink Joy or Lucky Plant, ( Crassula ovata). 

Being a succulent, it requires no care and is, from my experience, indestructible. 
The leaves hold the cool moisture inside. 
It is noticeably cool on the hottest of days and my girls spend the whole day resting under its shade.