I have a santa rosa plum tree that has been fruiting for about 20 years. The fruit is plentiful and delicious. However, we have noticed that every year the fruit seems to be smaller. Is there anything we can do to encourage larger fruit? I live in Southern California in the west San Fernando Valley. I do not use any sprays on the tree. I would appreciate any suggestions short of "culling" some of the fruit because that isn't practical.
Well, short of actually culling some fruits (about 10% of them) from the tree, there really isn't all that much you can do about the gradual shrinking of the fruits. In my experience with plums, fruit size is a direct correlation to age of the tree, and as they get older, the fruit naturally gets smaller.
Culling some of the fruit is not practical. It's a large tree and I use a ladder and a "picker" to reach most of the ripe fruit. Thanks for answering.
In order to obtain SOME larger Santa Rosa fruits you do not have to cull the entire tree. Santa Rosa plums do not received energy from the tree's entire foliage area. Each plum's energy (photosynthetic sugars) is manufactured by the leaves in a direct line above the fruit, and very little energy to no energy is received from leaves more than 2 feet distant each fruit. Culling a branch will increase the fruit on that branch. This is also the same process for citrus. - Millet