see link ... there is even a tab for videos ... its a system for many shrubs.. you dont need info specific to MO ...

its usually done over 3 years ... but you can go heavier ... but in some cases.. you might give up bloom next year ...

on the other hand.. many flowering shrubs are what i call.. run them over with the truck types ... and you can get carried away.. with not much long term impact ... keep in mind.. there will be no injury to the root mass .. so it can come back real fast ...

stick your head in there.. and tell us what you see ... count how many trunks ... first.. take out anything more than 3 inches ... then work on the two inchers ... then walk away.. next year.. after bloom ... take the next two sizes.. etc ...

i dont think you can hurt the thing .. lets see what others say ...just make sure you leave a good number or half inch or so trunks.. it will be back to 8 feet by next year.. lol ...

ken

https://www.google.com/webhp?ie=utf-8&oe=utf-8#q=rejuvenation+pruning

Ken is right, as usual, but keep in mind that mock orange blooms next year on the growth it puts on this year - those long, long whippy branches that are going to show up very soon are what will bear the blooms next year, so don't cut too many of them while you're pruning.

@ken, how many trunk trunks? Hundreds? This MO is a giant. And do you mean 3 inches from the ground?

A different question - what does one do with all the cut branches and detritus? I've been spending a fortune on contractor bags. I remember my grandmother making great big bonfires but I don't think my neighbors will approve of this method.

I'll take a photo of the inside and post.

Identify the largest/oldest trunks and cut them off as close to ground level as possible, removing only a 1/3 of the trunks/stems in total. Next year, do the same and again in the third year, each year removing only a third of the total stems. By the end of the third year you will have fully rejuvenated your shrub. This reduces the size of the shrub (temporarily) while still maintaining sufficient old growth to support flowering.

As to the disposal, cut up the branches into smaller sections and put into your yard waste recycling. Or buy or rent a chipper.

Thank you all for your great advice! Here are some photos:

The mock orange that ate New Jersey!!

10 ft. tall is typical for various Philadelphus including the frequently mentioned 'Virginal'. Renewal pruning of examples such as the one shown here that have not been kept up (no individual canes should be more than 5 years old) consists of cutting the whole thing down to the ground during winter, spring or immediately after flowering.

I second that! This is chainsaw time - unless, like around here, you have folks adept with machetes. If you tried to 'rejuvenation prune' that you'd have to set aside a month to do it!

Sara