@KG: I suspect the seedlings have a much greater survival rate in pavement and patio cracks because they get the perfect little environment with moisture and shade, away from pecking birds and heavy feet.
Well, I have been itching to prune back some of my shrubs after a little epiphany hit me last night. I Love foliage and the shapes plants grow into (especially those small shrubs that naturally grow compact rounded shapes) and have always wanted but never owned any box hedging/topiary. A few reasons including price, time, lack of know how and fear of ruining things have put me off over the years until now...
I realised, rather belatedly, that other species besides box can be trained and clipped into shapes and I adore pruning things...I adore those shapes and everything small leaved and sculpted, so after some research, I discovered that my garden is full of perfect substitutes for topiary. I shall practice on the larger versions over the coming seasons and take cuttings to grow new topiaries later in the summer. 
I'm very excited and it seems like the perfect addition to my style.