I get asked about this striking Knautia all the time. It flowers from early June through the Summer, loves a sunny spot and will do in most neutral to alkaline soils. It self seeds a bit, but not aggressively and is the most wonderful shade of deep red which seems to fit into almost any colour scheme – somehow managing to go well with warm bright colours and cool pastels.
The plant itself is a fairly chunky thing, but not overly so and as the flowers are held well above on thin stems it has that translucent-ness which allows it to weave itself among other plants, and be ok right at the front of the border.
Its seed heads stay as these delightful lime green pincushions for a good while before they go brown and so later in the season you have the red pincushions alongside these bright green ones which is really rather stylish. (Although you might want to take my definitions of stylish with a pinch of salt!)
There is a pastel pinky mix called Knautia ‘Melton Pastels’ or something but why have pink when you could have that red?