I've not grown this variety of cleome before but I have grown Violet Queen very successfully. Seeds germinated easily in an unheated greenhouse in the spring.

this is a new variety grows 2ft like a miniature cleome shrub many more leaves ....seeds are not available as it will not come true from seed and has been bred for this colour the only way of increasing it is stem cuttings that i have never been good with in the past thanks anyway

I'd be tempted to try a range of techniques then. in water as you would bizzy lizzies, then no root hormone in a good compost and then some with rooting hormone and see what if anything works. I wonder if they micro-propagate them commercially.

people like sarah raven have them in this years catalog/website for the first time i wondered about saving the seed only to find that you have take stem cutting. i bought them cheaper as a late filler in june from sarah raven i think its best to just do the same again 5 for £10.00 i think but i think they were half pricein june if you look at some american sites they claim 3-4ft but mine are not much more maybe 30" at most make nice front door plants they are fairly drought tolerant