Small Yellow Immature Plums Dropping Sign of No Pollination

Q. I have two Santa Rosa plum trees planted in my backyard.  The one in the lawn area has about 25% small yellow plums that fall off when I flick them or shake the branches.
One is planted in a lawn area and the other in a rock landscape with a mulched area approximately 6ft. in diameter.  Both are doing well with numerous large plums growing.  The one in the lawn area has about 25% small yellow plums that fall off when I flick them or shake the branches.  The remainder of the larger plums look great. Is this tree getting too much water or is this a natural thinning process going on?

A. The yellowing fruit is a sign of a lack of pollination and they fall off naturally. Usually called “June drop” in some texts. I have some good pictures I can include later of plum with poor pollination. Check back after May 1st.