Raised Bed Dilemma!
Firstly, the question of standing raised beds on concrete. Although not an ideal situation for a raised bed, hard surface growing is certainly a popular idea as a number of our customers have placed their raised beds on a patio or in a courtyard setting, enabling them to grow vegetables in an otherwise barren area. And if the soil is clay as you mention in your message, it may not be worth the effort of breaking up and removing the concrete!
You will need to use a raised bed liner or a raised bed base to cover the issue of drainage and waterlogging, which will prevent leakage onto the surrounding area – and of course is less expensive and time-consuming than preparing the ground. As long as you are careful not to overwater and ensure plenty of organic matter is included in the soil, drainage should not be a problem.
Finally, the question of beneficial creatures such as earthworms entering your soil. It’s true to say that a concrete base will hinder the natural progression of these, and other creatures, into your beds but applying plenty of home-made compost will introduce many helpful inhabitants to your new beds. You can also introduce small amounts of garden soil – including earthworms - when filling the beds with compost and topsoil but in our experience of growing in raised beds, you find the soil is soon colonised by welcome invaders.
I hope this information gives you a better idea of what is required to set up your beds, but if you’ve any further questions or queries, please do not hesitate to contact me.
Many thanks once again for your enquiry and the best of luck with your project.