From the high mountains of Costa Rica comes this mystery Costus. I grew it from seeds collected at 1800 meters in an area of Costus wilsonii, which is what I thought it was until the seedlings matured and it finally flowered. For some time I thought I had a new species until the summer of 2011 when I returned to the collection site and solved the mystery. I now believe it to be a natural hybrid of Costus wilsonii with Costus villosissimus. It has the beautiful wide mouthed yellow flowers of the latter species and the green non-appendaged bracts of the former. I am calling it 'Mellow Yellow'.
Costus 'Mellow Yellow' is easy to grow and easy to bring to flower. I have grown it in large pots and it quickly reaches about 8 feet and forms flowers all summer long. The yellow flowers are quite showy.
I find it grows and flowers best in sunny areas, but have not tested it in full sun. I have not tested it for hardiness either but I an trying some outdoors in our mild winter of 2012-13 - not a very hard test - and will report on it later.