you have to have a groom at your stables and it'll automatically lay down the bedding in the boxes at your equestrian center.
Buy your chosen bedding from the EC stores so that you have it in stock. The groom will then change the bedding at the next update. When you next log on and check your EC the bedding and cleanliness stars will be starting to fill up. From Strawberry Fields on Howrse
The bedding which gives the best prestige is flax.
Try checking the equestrian center's FAQ. To get to it, roll your mouse over "HELP" near the top right. Click on "equestrian center faq" or "equestrian center frequently asked questions". you!!!
On Howrse, straw and flax are the best bedding for a mare who is due to foal.
for the equetsrian center, you go to the equestrian center's store and buy bedding
You should get 18m boxes, 100% fertile clean meadows, flax bedding for the boxes, get your comps running, get good horses in your EC, 100% health care, carrots, and health mashes.
You cannot gift stable boxes on Howrse.
they sell it in the secret store
The only way I know how is to put your horses in their boxes, and if you are lucky, you will eventually get a pot of grease.
The answer for Howrse is Straw.