Final assessment will be at Wisley on 3 June. Inga Grimsey resigned from the post on 9 September 2009. Gordon Seabright has been acting director-general ever since.
The RHS is seeking a candidate with a "consultative, transparent and consensual management style". Another of the 21 personal qualities required is knowledge of and participation in horticulture, "if only as an amateur gardener".
The RHS also wants someone to "create a one-team approach providing a consistent management style and set of values". No salary is specified.
The RHS is also advertising for six marketing staff for gardens, shows, membership and travel trade at £20,000-£25,000.
Head of marketing (shows and gardens) Laura McCarthy said the new travel trade marketing role reflects a new drive into the domestic and international travel trade market to widen participation in RHS gardens and events.
A role as web editor is also on offer at £22,000, with RHS general qualification required.