- M. Brunswick & Co. (3)
- Madson, M. G., Seed Co. (3)
- Madson, M. G., Seed Co. (W) (1)
- Magnuson, Louise (4)
- Manhattan Nursery (1)
- Manitowoc Seed Co. (W) (2)
- Maple City Nurseries (2)
- Maple Grove Nurseries (1)
- Marinette Seed Co (1)
- Marlow Seed Company (2)
- Marshalls Nurseries (NE) (2)
- Mattioli, Pietro Andrea (55)
- Mayer's Plant Nursery (2)
- McDonald, Susan (2)
- McDowell Ginseng Garden (1)
- McFarland, Terry (7)
- McFarland, Terry L. (1)
- McGreer Brothers (1)
- McKay Nursery Co. (2)
- McLean, J.H. (1)
