In his oblique, Victorian manner of speech, Prince Charles points out that "one of the great difficulties associated with the adoption of organic or, perhaps more appropriately, sustainable principles at the time I started turned out to be convincing others that you had not taken complete leave of your senses."
In other words: "Look out, you'll have to read this very carefully in order to understand it". I don't find much that is oblique about this sentence. It may be less straightforward than the Washington Post habitually serves up to its readers, but I would venture that anyone with average reading skills should be able to grasp its meaning on the first read-through.
The entire article on Prince Charles' visionary work in the field of sustainable gardening can be found here.