|Before (left) and after.|
Planted in August 2009, our Philadelphus was supposed to be a nice 5' tall shrub covered in scented white blooms, sitting by the bench and perfuming the air. In 2009 it was small, in 2010 it wasn't much bigger. In 2011 I kinda stopped caring, and in Spring this year our friend Corinne said she thought it would never be happy. Then....Bingo! It flowered beautifully, scentedly, and relentlessly. It's finally finished flowering and I am glad I waited for it to get it together!
The time to prune is after flowering but not too late into summer. The plant flowers on growth from the previous year, so if you start hacking at it in the fall or winter it won't have time to make new growth to flower on. No flowers for you!
The rule to remember for pruning them is "thirds." First, cut back all the stems that flowered leaving 1/3 of the length. Next, prune back 1/3 of the stems down to the ground.
Pick stems to cut right back that are deep in the heart of the shrub, all dense and tangled. Don't cut back new growth that had no flowers.
And voila! Good to go for another year.