Keith's lemon, like your celebrity juice prog. I'm in sw Cornwall and can grow tender plants easily.these usually propagated easily and made Impressive flowering plants v quickly. I did it as hobby, albeit a profitable one. From home. I sold plants that people could see growing well .....hopefully impressively well.......in my own garden. Margins are difficult but the big boys are charging a lot these days for plants that you could produce cheaply.......how about trying bedding plants? I see yu are in east Devon, bit colder than me. Do you grow many plants yourself? I split stock plants to keep my own young n healthy but also to sell. Cannas were good. Huge clumps in garden were split n potted, gingers, grasses, dahlias, campanulas, oh, so many. Show you know your plants and give advice add to your sales package