There are some plants that can go it alone but most need mass to be noticed. The more densely you plant the less room there will be for weeds to grow.

Plant in odd numbers – three, five, or seven – to give your garden a sense of informality and movement. Design concepts from other disciplines – art, photography, graphic design, and interior design – apply to the garden also. Check Not Another Gardening Blog for advice on Unity of Three – arranging elements in groups of three (or odd numbers).