I have a shrub in my garden which is around 6 ft tall. I found it growing in the garden when it was quite small and moved it to another spot thinking that it was a buddleia. It has been in about a year now, hasn't flowered yet and it has square stems like the mint family.
I broke off a bit and crushed it, but it has no smell.
Has it flowered Monika. The only thing I know of with square stems is the lovely verbena bonariensis which can get to that height & shrubby if left.
There is also salvia family that has square stems..sage and other flowering salvias..perennial types, not the bedding types. Buddleias have round stems so it would not be that.
What are the leaves like..size, shape, colour, texture and how are they positioned on the stem. Bit more idea how the plant look would help.
I have a couple of photos now:
(http://i5.photobucket.com/albums/y165/godley/mystery2.jpg)
(http://i5.photobucket.com/albums/y165/godley/mystery.jpg)
I can see why the leaf shape made you think buddleia.