By Canalhopper
Denbighshire,
United Kingdom 
I have a Spirea Douglasii.
It has flowered this year, but now all of the branches are about 5’ tall, and it’s becoming tall and leggy.
I’ve looked up details of how to prune it, but get different results.
Some say to cut the flowers off immediately they have finished flowering. Others say cut it down to the ground as it flowers on new growth. Some say to do this in the autumn, others to do it in the Spring.
Has anyone any advice, please?
6 Dec, 2020
this is the info generally about the plant
https://www.rhs.org.uk/Plants/22834/Spiraea-douglasii/Details
this is specifically about pruning technique
https://www.rhs.org.uk/advice/profile?pid=197
Usually you just dead head after flowering but if it needs renovating it can be cut back hard after flowering. Having said that if you cut it back hard in the spring you will not have any flowers in 2021. But at least it will be a decent size.
If you don't want to forfeit all the flowers remove half of the tall wood evenly round the shrub this year and the rest immediately after they have flowered.
6 Dec, 2020