We have a plum tree quite near to our party fence.Where it came from I know not probably from a "stone" dropped by a bird.For the past 3-4 years it has started to bear fruit but only 5-6 plums at a time.Is there any way of increasing the yield please??Thanks!!!
Wait for a few more years...but also pruning the long growth back to about 4 nodes will help
lots of pruning guides out there RHS have guides for all sorts of fruit trees
You can grow it from a plum seed but it may not be anything like the mother plant . Normally plum and apple trees are grafted on to a known strong root stock . In that way you know what you are going to get.
If you don't have a 'plum tree' neighbour. . . you may need to buy another tree for cross fertilisation. A dwarf plum on St.Julian stock will help and you can keep it in a tub close to the 'birds present' self seeded tree. This is what we are having to do.
Wait for a few years I have one and about 4 years ago we did not get that many off it. This year has been the biggest year of Plums it was said. I got 4 pounds of plums out of my tree.The tree has been here for 12 years. Keep waiting and in a few years time you may get some more!