I bought 2 recently and the flowers have gone, but there is still a lot of new growth coming through
Do I just prune as I go? I wouldn't even know where to start pruning as some new growth is coming through right where the flowers used to be. Or do I jus leave it and let it do its own thing?
(Picture might be hard to see, the sun is so bright!! (Not complaining or anything))
It's up to you. Either leave it to grow or else prune back any stems that are too long or in the way as soon as flowering finishes.
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
The aim is to provoke the plant into producing new growth from low down which will make a strong new structure for what will become a three, four, or even five foot tall shrub. Yes, it's tricky when the new growths shoot from high on the stems like that, but you prune it to shape, removing quite a bit of the flowered growth and the plant will react accordingly. Don't be frightened about pruning out too much. It's a spiraea, you won't kill it.
I've just hacked one of mine back as I'm moving it. You really can't go too far wrong with them.
They naturally go up, and then 'fall' outwards, so prune it to the way you want, but keep that shape in mind so that it looks fairly natural. At this time of year, it'll quickly produce new growth
I live in west central Scotland - not where that photo is...
I prune off all the flowered stems back to a new growing shoot. If you do it now, as the flowers have finished the new growth ripens enough to flower next year. If you leave it until later, you lose next years flowers.