Ok this is one of my favourite subjects and anyone who has come across any of my gardens will know that I use a lot of plants but not many varieties. The reasons are simple, the less objects vying for your visual attention the more peace full the garden appears. I have seen gardens where there may be 5 or 6 species planted and they look absolutely stunning and not boring as you may think. Of course it also depends on the size of the garden and various other factors, such as scale, terrain and climatic conditions.
So next time you think about your property try and visualise large drifts of plants, play with colour, form or texture contrast. Varying heights of plants and accentuate with some specimens to create focal points, use repetition and never plant in lines, stagger them in odd numbers if possible. Use built elements to enhance and or accentuate the plants, put in some water which creates movement. Lighting is also great when used with restraint and can liven the outdoors after sunset. So next time you are at the nursery buy 20, 50 or even a 100 of one variety and get digging, I guarantee you and your guests will love it.