Following on neatly from Orchard, John Fowles's The Tree is, as William Fiennes describes it in his foreword, "a sui-generis polemical memoir-essay". It's a collection of recollections and observations, suitably dendritic in form, ranging from anti-Linnean sentiments to a skewering of the essence of art and Fowles's own creative process. It's a short book but it offers much to think about and would, I am sure, repay re-reading.
Just by the way, I wouldn't have thought of bracketing JF together with Elizabeth Goudge, but among several references in the book to paintings is one to a favourite work of his, Pisanello's The Vision of Saint Eustace ("this ambiguous little masterpiece"), which features so memorably in Miss Goudge's The Herb of Grace.