Join Sarah and Mr Pottifer in their magical plant shop, where fantastical creatures grow from trees! A new customer at the shop buys some mermaid seeds, and Sarah is only too happy to help him grow them. But when the plants are accidentally given too much sugar, their vines spread throughout the town, flooding the streets and causing a whole heap of MER-MAYHEM! Can Sarah and her new friend use their quick thinking and green fingers to save the day? This hilarious story celebrating friendship and kindness is the third magical adventure from the author and illustrator of the bestselling stories How to Grow a Unicorn and How to Grow a Dragon.