Although purists may insist on native plants, a well-planned woodland garden can carry exotic wild species and even certain hybrids without losing its natural look. The secret is to use plants which give the impression of being wild--plants with small simple flowers and foliage which is not abnormally marked.
In the wild, woodland plants grow where there is a natural covering of leaf litter. In an artificial wild garden, such plants as primroses, trilliums and epimediums grow better with plenty of organic matter in the soil. Fertilizer will ruin the character of wild flowers.
Nigel Colborn, 'Shortcuts To Great Gardens'