re victoria plum tree

Stone fruit like plums should be pruned in June-July really. Strong side shoots are mostly the object of pruning and can be reduced to 5 or 6 buds from the older branch it came from. The main reason for pruning at this time of year is to reduce the chances of getting silver leaf disease which is fatal to the tree.

You can reduce height now if you want and crossing branches but don't do the whole thing or you will lose potential flower and fruit next year as the tree will try to replace it's canopy with growth. Make sure you seal large prunings with a propitiatory tree wound sealant straight away too.