I have 2 European plum trees that produce a purple plum. They have been growing at our place for 15 yrs. Each tree is alway loaded with fruit. They get to be about the size of a pecan and are turning purple and then they all fall off. Never have any ever reached maturity. People said we needed another variety so we planted a yellow plum last year(European). It did not blossom at the same time and then we received a frost when it did so no fruit from it. I’m wondering if there is some other reason we are missing. Have sprayed them prior to blossoming 3yrs in a row to no avail. We have various apple and cherry trees growing and also peach trees. All produce an abundance of fruit without any spraying. This year we are dryer than normal. However Evan in wet years it dies the same thing. The trees get full sun. They are the edge of our field. We are in climate zone 6b.
Thank you for contacting the Toronto Master Gardeners concerning your European plum trees.
There are a number of reasons why a fruit tree might prematurely drop its fruit. It could be environmental, pest related or natural. Premature fruit drop is nature’s way of reducing a heavy fruit load. According to the Ministry of Agriculture and Rural Affairs (OMAFRA) “It is usual for a number of young fruits to drop off during the spring and early summer. This natural thinning is often referred to as the “June drop”. With most cultivars, too many fruits will likely still remain on the tree. It is often necessary to remove the excess fruit by hand when it is still very small”
Fruit thinning reduces limb breakage, increases fruit size, improves colour and quality of remaining fruit, and stimulates flower initiation for next year’s crop. The Royal Horticultural Society article Fruit Thinning recommends “fruit thinning is best done after the June drop and should be completed by mid July – thin fruit so that there is one fruit every 5-8cm or every 15 cm for a pair of fruits.”
Environmental factors such as a late frost or excessive heat, cold or changes in humidity can also cause premature fruit drop.
You do not mention seeing any pests or diseases on your tree. Usually premature fruit drop from pests or diseases occur late in the season so I do not think that this is the cause of your fruit drop, refer to the University of Manitoba article on Premature Fruit Drop.
The fact that you have seen this happen for the last 15 years and each time the trees are loaded with fruit makes me suspect that your premature fruit drop is the trees inability to support the vast number of fruit that it has produced. The thinning of your fruit should solve the problem.
You may be interested in the article Improving Fruit Set in Plums put out by the Ontario Fruit Growers.
Good Luck with your plum trees.