Chapter 111 of the General Laws is hereby amended by inserting after section 32A the following section:—

Section 32B. No ordinance, by-law, or regulation shall prohibit, unreasonably regulate, or require a special permit for the use of land for the primary purpose of commercial agriculture, aquaculture, silviculture, horticulture, floriculture or viticulture, except that all such activities may be limited to parcels of 5 acres or more in area not zoned for agriculture, aquaculture, silviculture, horticulture, floriculture or viticulture. For such purposes, land divided by a public or private way or a waterway shall be construed as 1 parcel. No ordinance, by-law, or regulation shall exempt land or structures from flood plain or wetlands regulations established pursuant to the General Laws. For the purposes of this section, the term "agriculture'' shall be as defined in section 1A of chapter 128, and the term horticulture shall include the growing and keeping of nursery stock and the sale thereof. Said nursery stock shall be considered to be produced by the owner or lessee of the land if it is nourished, maintained and managed while on the premises.