Or wait for a couple to fall. I forgot about my Santa Rosa because I have a very spread out orchard and most years the SRs are pilfered by birds. This year all such pressure, bird, rodent and even coon is way down and walking by I noticed a few SR on the ground. I was afraid all fruit or most fruit would be over ripe and mushy, but even the fallen fruit was still delicious and as firm as needed for my tastes. Some of the fallen fruit had bird pecks on it so they find it difficult to eat from the tree as they fall from the first peck. They don’t usually like to risk feeding while on the ground unless it is protein, like seeds, apparently. Most of the on-ground fruit didn’t appear to have been pecked off, though.
However, most plums don’t fall when ripe and prune plums will simply gradually dry out and become their namesakes if weather is fairly dry. That used to be how it was done in CA. I spend a great deal of time feeling every fully colored plum on my trees before harvesting them- until I get to the point that I just don’t care and shake the trees until the ripe ones fall. This works OK with prune plums, but J. plums are more likely to split although I suppose you could spread straw or something beneath the tree to protect from that.
