In this case I mean having 2 greens on each hole, as the PGA Tour Zozo course does this week and many Japanese golf courses do as well. I always understood that one green had winter grass and one had summer grass. But this week, they're playing both greens on one par 3, and a commentator said that it was because of the "heavy play" that they had two greens they could alternate between on each hole. And they certainly don't look like different kinds of grasses.
Any information?
According to my friend Masa, the two-green system was actually suggested to the Japanese by an American military officer stationed there after W.W. II. He was from Georgia, and he mentioned that where he grew up, some clubs had a summer green and a winter green. The better clubs in Tokyo adopted this strategy [the sub greens were not designed by Hugh Alison], and then when golf in Japan boomed in the 1960's, everyone copied the best clubs, which had two greens.
Usually, back then, there was a bentgrass green and a korai (Japanese zoysia) green, but some clubs in Hokkaido just built two bentgrass greens side by side. Eventually, as turf maintenance standards became higher, many of these clubs converted their sub green to bentgrass as well. But older members did not want the "traditional" sub green to go away, so most clubs kept them, unless they had an American architect and agronomist talk them out of it.