The award-winning garden writer and Ground Force presenter will be in store from 2pm to 3pm.
Titchmarsh's BBC books have hit the top of the gardening book charts since their release earlier this month. The TV gardener is preparing for RHS Chelsea Flower Show, where he will co-present with Joe Swift.
James Wong, Carol Klein, Lila Das Gupta, Nicky Chapman and Andy Sturgeon are among the other Chelsea presenters. The RHS talks stage will be hosted by Wesley Kerr, James Alexander-Sinclair and Jane Owen.