i am no Philadelphius expert .... but in general with big shrubs .... i can offer the following.. since no one has answered ...

pruning off the tips.. will probably take off next years flowers .... and only make it more wilder at the top ...

i would treat it as i would a lilac/weigela/spirea .... i would go into the heart of the bush .. and remove the three biggest limbs in the center.. as close to the ground as possible .... next spring i would do the same ... and next fall the same ....

as you remove the large branches.. new leaders will start emerging .. and the plant will diminish in size ...

you will need to do this every year .. forever ...

doing it this way .. leaves branches for next years flowers..

i do NOT know if it a plant that can just be cut to the ground.. and recover .... and i don't know how aggressive you can be .... nor the proper timing ...

but bottom line.. GET MAD AT IT ... and teach it a lesson .. lol ... i doubt you can harm a monster like that in the long run .... thought googling Philadelphius or even better the proper spelling.. lol ... may give you better info ...

i love to be corrected when i am wrong...

good luck .. now go teach it a lesson ...

Ken

Here are a bunch of Google hits on Philadelphus coronaria pruning. There seems to be two schools of thought on maintenance pruning, but Ken is spot on about rejuvenation. Take out a third of the old stems, to the ground, every year for 3 years. Do it in late-winter to early-spring, before leaves emerge.

After that, some references say no pruning is needed. Others say to prune it after blooming. You'll have to experiment.

Here is a link that might be useful: Google hits on Philadelphus coronaria pruning

You can certainly cut it back as far as you like and not kill it. If you can bear to be without the flowers for a year, do it all in one go. Maintenance pruning is only necessary to keep it to size. Philadelphus flower on old wood.

Hello...........I have decided, for good or evil, to just prune my mock orange "monster" all in one great go. It has, naturally, stopped flowering for the year.I now need to know what time of year I should do this. I do realize I will probably have no blooms next year, and while that will be rather sad, I need to get this creature under control. Hopefully someone out there can tell me when to do the dirty deed. Thanks so much.
Greenlydia