Columbia Road Market is one of the most popular flower markets in London. Located in East London, the street is the home of over 60 independent shops and stalls. It opens every Sunday from 8am to 3pm and as long as you are prepared to deal with crowds you are in for a great deal.
There are great selections of house plants for amazing prices and few shops that sell the cutest planters and pots. My favourite one is called PotLuck and it's just at the entrance in the market.
The market is packed with tons of outdoor and indoor plants. You can find amazing deals on Calathea/Prayer plants, ferns, lots of succulents and cactuses, different varieties of rubber tree plants, some huge beautiful monstera plants (on my last trip I saw some big ones for £20) and Alocasia Polly, and even olives and citrus trees.