Just taking note of this while I think of it. It stands out in its omission of Villandry but the other gardens are less well known so a really good list

From Touraine Tourism Board

• the contemporary creativity at Rivau,
• the 600 tomato varieties at la Bourdaisière,
• the orange trees at Chateau Gaillard,
• the poetic roses at the Ronsard museum,
• the rare plant species at the Valmer kitchen garden conservatory,
• the botanic garden and the Gloriette park of Tours,
• the skill for the ‘potager au carré à la française‘,
• the elegance of the park of Richelieu and one of the castles of Amboise, Ussé and Chenonceau,
• the surprising Pagode de Chanteloup, 
• and the village-garden of Chédigny and its 800 varieties of rose bushes.