Victoria Plum tree pruning.

Welcome to GC

It's recommended to do summer pruning, to avoid possibility of silver leaf, and to do it immediately after you have picked all the fruit - so you benefit from the crop.

Unfortunately, plums tend to produce suckers and they can be quite a nuisance as they can appear almost anywhere within 20ft of the tree. Try and cut them below ground level as it seems, from what I can see in your photos, that you have grass around the tree. Pulling is normally recommended but can be a problem in lawns. Otherwise the suckers, if cut at ground level, will gradually form large knots that could damage your mower.

The other problem you have is the size of the tree. You're not going to be able to pick fruit from the upper parts because it's too high so it needs drastic reduction. Unfortunately, plum trees aren't too keen on heavy pruning. So you have to decide whether to take the chance that it may not survive if you prune it hard.

If it were mine, I'd be inclined to prune hard - take out the main centre stem down to at least 10ft now and, this year after fruiting, prune the other branches back by about 5ft and thin out crossing or damaged branches. I would use Arbrex on all the thicker cuts. There is a train of thought that sealing cuts is no longer necessary but I always do it for my plum trees (I don't bother on apples or pears).

If you have other large trees that need pruning I would be inclined to ask a tree surgeon to come in and give you a quote for the lot. One tree can be relatively quite expensive but a number of trees can working our very reasonable. The other year they quoted me £50 for a fairly large plum tree (quite reasonable) but only £100 if I had ten other, smaller, trees done. At that price it wasn't worth my while doing it myself. There's usually a big difference in price depending on whether you want them to take the prunings away (or chip them) or whether you will dispose of them.

Good luck