The “R” rule may have been true 30 or 40 years ago, but thanks to advances in aquaculture it has fallen by the wayside. It used to be fishermen dug for oysters only in the colder “R” months (September through April) to avoid the spawning season.
Warm waters (above 60 degrees) encourage spawning, rendering oysters bland, soft-textured, and small. Once the spawning season is complete, oysters are generally plumper and better-tasting, thus commanding a higher price tag.
Today’s oysters are more likely to be farmed than found, with farmers having more control over the conditions in which they are grown, harvested, and stored. This means that oyster cultivators can plant oysters in cold waters, thereby staggering spawning and keeping their product available year-round. So forget the “R” rule—any time is fine for eating oysters.