"Green"/ecological gardening is native gardening, and vegetables, plus other consumables, should be the only exotic-flora we plant or hybridise - as doing so can help limit food-miles, etc. By filling our other garden spaces with natives, we limit the risk of foreign-diseases and -pests, plus use less water and other resources, whilst aiding the native-fauna that, over the centuries, evolved with them. (You have probably heard of American skunk-cabbage and Japanese knot-weed, among other big-problem species, but even high-nectar exotics, such as Buddleia, that are very attractive to some of England's native-fauna, should be avoided, because they upset nature's/God's balance – God created evolution, too, that is; so the Victorian plant-hunters were brave but wrong and, rather, it is better, for example, to grow geraniums in England, and pelargoniums in South Africa.)

Our green gardens, with their edibles and natives (harvest and habitat), can be made still-greener by the addition of compost heaps/bins; a wildlife pond – for native frogs, newts, and so on, rather than exotic goldfish; bee- and bird-boxes, plus carefully-selected regularly-cleaned feeders; rain- and grey-water butts; by growing everything organically - including thrifty home-propagation, plus species-swapping; and by leaving lush untidy patches, with decaying branches (insect hotels).

For those who agree, there are books and nurseries, some run by local councils, offering native plants and information on them.

P.S: whilst our selection of indoor plants is, logically, not as critical to the ecology of our greater environment, we need to be wary of importing foreign diseases and fauna in plant pots and, thus, lean toward home-grown (from here).