This is the kick off to Denver Botanic Gardens' Urban Nature exhibit and as such is priced to be the best deal possible. You can read the talk description and register online but Panayoti Kelaidis, a Denver gardening fixture and Colorado horitculture institution, endorsed Rick and this talk thus:

I think Rick Darke is far and away the greatest mind and finest artist in American horticulture today. I have heard him speak three times in the last year or so, and each time I have been more deeply impressed with the breadth and depth of his artistic talent and his intellectual prowess. He is a giant talent who has a fascinating story to reveal. You must not miss this.
He is launching Denver Botanic Gardens' exhibit of the year, entitled 'Urban Nature', and I think the talk and the exhibit will be landmark events. Rick has stunning credentials: he was curator of collections at Longwood Gardens for many years, creating some of their finest exhibits. The rather constricting climate of Longwood at that time (happily no longer: that is another great story to tell) led him to launch his own career as author, lecturer and designer.
His books are all now classics (impeccably written, stunningly photographed and designed with great content): check out his website to get a better taste for what he's up to: www.rickdarke.com.
And his talks are a revelation as how horticulture provides the essential tool that humanizes and might ultimately save a world that is careening through technological and mechanistic excess. Rick's understanding of cultural landscapes, and their ability to relate to young people, to those in urban environments, has given me great hope and new tools in my day to day work. Harriett MacMillan (gardening guru at Echter's), who heard Rick's incredible talk at Progreen last January, made a similar plea at a recent Plant Select Propagation committee meeting.
The joke is on you, folks, if you miss this event. It is the launch of our single biggest program of the year ? Urban Nature ? and I just know you want to be here to kick it off in style with Rick Darke. Be there or be square!

That's just fantastic praise. Again, here's the talk description and registration and I will repeat that the prices quoted are very modest for the caliber of speaker he is.