Alan Titchmarsh and Rachel de Thame discover how the themes of water, boundaries and the British countryside are dominating the exhibits at this year's Chelsea Flower Show. Chris Beardshaw is in the show gardens unearthing radical ideas for sustainable horticulture. Plus 2011's 'Best in Show' winner Cleve West explains why topiary is a hot topic. And designer Jo Thompson reveals why her journey to build her show garden began with a caravan. Show less