Here is a list of beneficial herbs that are grown in 5b near me for chicken health boosters: (dried and added to the nesting boxes)
Catnip - calming sedative, insect repellent
Dill - antioxidant, relaxant, respiratory health, stimulates the appetite, aids in digestion, promotes feather growth
Fennel - laying stimulant, boosts reproductive health, insect repellent
Garlic - laying stimulant, anti-fungal, benefits circulatory and respiratory system, relieves diarrhea
Lavender - stress reliever, increases blood circulation, highly aromatic, insect repellent
Citrus Peel- highly aromatic, lowers stress, antibacterial, repels rodents
Marigold/Calendula - vibrant egg yolks, insect repellent, antioxidant, laying stimulant
Marjoram - laying stimulant, decongestant, improves blood circulation, detoxifier
Mint - insect and rodent repellent, antioxidant, aids in respiratory health, digestive aid, antiseptic, stimulates nerve, brain and blood functions
Oregano - an antibacterial, anti-inflammatory, combats coccidia, salmonella, infectious bronchitis,
Sage - antioxidant, anti-parasitic, general health promoter, thought to combat Salmonella, laying stimulant
Rose Petals - highly aromatic, high in Vitamin C, antioxidant
Rosemary - pain reliever, respiratory health, insect repellent
Thyme - aids in respiratory and immune system health, antibacterial, antioxidant, anti-parasitic, laying stimulant, insect repellent
Chickweed- helps with inflammations of the digestive, renal, respiratory and reproductive tracts
Bay Leaves - antiseptic, antioxidant, immune system booster, insect repellent
Ginger - stress reducer, anti-oxidant
Cinnamon - promotes healthy breathing
Raspberry Leaf - antioxidant, relaxant, supports healthy reproductive system.
Alfalfa-high nutritional value, abundant source of protein, essential vitamins (including A, D, E, K and the full family of B vitamins) and minerals (biotin, calcium, folic acid, iron, magnesium, potassium
Dandelion - general health tonic, laying stimulant
Cayenne pepper - aids circulation, appetite stimulant, antiseptic, digestive enhancement
Chamomile - kills mites and lice, repels fleas, antiseptic, anti-inflammatory, antibiotic, calming, detoxifier
Basil - antibacterial, mucus membrane and respiratory health, orange egg yolks, repels flies and mosquitoes
As for run material, I have never been able to keep anything alive planted in the run, we have to grow them in pots and add to the run in a pot until they eat it. Sawdust or sand would be the easiest to keep clean, you can rake up the poo pretty easily with either. Gravel does not sound good to me, I can not imagine how to keep that clean and I wouldn't guess that they would like to walk on that, plus extreme temps might cause a problem for their feet. My ducks and geese just run free on my property and nibble whatever grass they want, so they don't deplete the grass, plus the droppings fertilize the grass. The chickens will soon be moved to summer chicken tractors, so I don't have to mow or grow them plants. I have no idea how to grow plants in the run for them, as it's covered to keep snow and rain off, please let me know how it goes for you.