Hard pruning philadelphus?

turmeric

With all this time at home one of my neighbours decided to cut back her old hedge back to reduce the width, but in doing so she's found three philadelphus shrubs inside it.  Heaven knows how long they've been hidden but they're now fully exposed and she wants to improve them.  All three are about 6ft tall with leaves on the top 4inches only. One has only one stem (about 1.5inches diameter) which forks halfway up, the other two have two branches coming from the base (again about 1.5 inches dia).  All three have lots of twiggy branches with sparse leaves, but only in the top 10-12 inches where they were at the top of the hedge and managed to get to the light I suppose?  Our question is how to bring them back to healthy, bushy shrubs.  She's loathe to cut any stems back hard as there's hardly that many there already! And we're not sure new growth will come if they have a sudden hard prune.  Any help would be much appreciated. She really doesn't want to remove them as she's so pleased to have discovered them.  Many thanks all.

Obelixx

I would give each one a generous feed - pelleted chicken manure, blood, fish and bone, rose or tomato fertiliser - and a bucketful or two of water.   Then sit back and wait and see.   Philadelphia flower on old season's wood so you need to leave the stems to see which, if any, flower.  The usual time to prune is once flowering finishes.

Assuming they are still viable and respond to being fed, they may produce new stems from the base in which case all the old ones can be cut out to give them room, light and air or they may produce new leaf and/or flower buds from lower down on existing stems in which case I would then cut back the non responsive stems to the base.

An alternative would be simply to cut out one third to a half of all the stems at the base now, choosing the oldest, thickest stems after feeding as above.   Then next year, after flowering, she can cut out all the rest of the old stems.   In future years she should cut out one third of all stems each year after flowering, choosing the oldest, and that way the shrubs will be renewed every 3 years and stay vigorous.   They should be fed each spring.

turmeric

Thanks Obelixx.  Looking at them I think they'll just develop leaves and possibly flowers on the tips as that seems to be the only bits with any sign of life.  I would usually have told her to risk cutting out the oldest stems to encourage new growth from the base but as they have so few main stems (only one in the case of one of them!) there really isn't a choice of 'older' stems to cut out.  I'll tell her to feed and water them and see if that produces anything.

Obelixx

OK.  Feed, water, wait.