Plants shown are Sansevieria Futura Simplex, the gold one, and the almost black Sansevieria Nelsoni.
In the latest edition of the American Garden Design magazine, there is a feature on growing Sansevierias, known as 'Mother-in-Laws Tongue'. I gather in parts of the USA they are a favourite of garden designers as they grow like weeds when planted outside. Here in Britain we only know them as houseplants.
They can though be used as summer bedding in containers looking stunning tighly packed together. They need though to go back under protection for winter though I read that they will withstand temperatures down to 28F/-2C as long as they are kept under well drained conditions.