There are usually several reasons why this problem occurs.
The most common of these is moisture deficiency.
When planting such a fruit tree, it is necessary to take into account that its roots cannot take the necessary moisture from the depths, since the root system is quite superficial.
Therefore, in hot weather you will have to water the plum.
Don't forget about mulch.
In this case, you can protect the roots from overheating and retain moisture.
Also, one must not forget about fertilizers, otherwise one can lose a significant part of the ovary if the plant starves.
But before adding additional funds, it is necessary to pre-water the tree trunk circle.
The garden should be checked periodically for diseases and pests. After all, it is very easy to lose a harvest of tasty and healthy fruits because of the codling moth or plum sawfly. You can save the harvest if you take measures in time.
