depends on your goal .. and how much time you want to wait.. for them to fill in ...

ken

Hedges often have much closer spacing than would be used where fully developed specimens would be intended to end up just touching one another. Or overlapping to a much lesser degree than within a dense hedge planting. If you have bought them already try laying the plants out and seeing what seems to you to be an adequately close spacing at this time. To a certain extent when they are to meld together into a dense row you really can't put the plants too close together. Of course, if you start out with them absolutely packed together at a small size there is some likelihood of stunting occurring later due to the crowding.

I'm inside now, of course, but my mature plant is maybe 4-5 feet across, so if you plant them 4 feet apart, you should be OK. Not a plant I'd choose to have a lot of--nice, but nothing to write home about. Of course, like all spireas, they are highly deer resistant.

I was thinking more of a spacing 80cm (2.6 feet). Do you think that would be a good spacing? I want it to be a hedge not single plants barly touching each other. Thank you

Anyone else have this as an hedge?☺

IME most if not all Spiraeas put out an increasing number of stems from the base over time, so they will get denser/wider to some degree. As Ken said, it depends some on how fast you want that dense hedge. I haven't ever seen Tor used as a hedge; I have the feeling that it might be a bit homely for the half of our year that it doesn't have leaves.