From ArborWiki

Gardening in Ann Arbor

Downtown Home & Garden (formerly Hertler's) sells garden supplies downtown, as do numerous other shops.

The City of Ann Arbor's Solid Waste department has a Materials Recovery Facility Drop-Off Station where you can buy bushels of mulch and compost.

[edit] Disposal

The Cities of Ann Arbor and Ypsilanti both offer free curbside pickup of compostable materials on your trash day - just leave your yard waste at the curb in a labeled trash container (stickers are available free from the city) or in lawn-leaf bags. Trash bags are not accepted. Bundle branches that are less than 6 inches thick into 3-4 foot long piles.

Leave your grass clippings on the lawn - it's good compost!