Use bamboos rather than tall grasses if you want evergreen plants. Bamboos come in two forms clump or runner, avoid using runner bamboo. Any of these bamboos will look good in a garden and will grow to between 9 - 12 ft tall [url]http://www.plantsforimpact.com/?cat=32/url]. There is also a new bamboo - Himalayan blue which looks fab. If you plant them in the ground you can use a root barrier to contain them however clump forming bamboo really does not spread that fast. Or in pots however, the bamboo roots will eventually break the pots, unless you lift and split the bamboo every couple of years. Planting bamboo in pots will mean that you have to water them - like grasses they get thirsty.

Use grasses rather than bamboo if you want an easily manageable plant. N.B. all the ornamental grasses are deciduous, so you need to opt for something like Miscanthus sinensis 'morning light' which has a wonderful appearance when Autumn arrives as its variegated leaves die off and they start to twist and spiral in all manner of degrees, very pretty - will grow to about 2M http://www.realoasis.com/Floral%20Hi...ng%20light.htm

HTH