The best way to get lichen to grow is to provide a friendly environment for it, and allow it to find its own way there. See this article for tips on providing a lichen friendly space.

Most lichens grow very, very slowly, often less than a millimeter per year, and some lichens are thought to be among the oldest living things on Earth.

         For those that want to remove lichen - it is not recommended that lichen be removed from an organic garden, as it is a good indicator of the absence of pollution and also harbours beneficial insects - but if necessary, try water-blasting, rubbing, scrubbing or a certified organic weedkiller.