Compost for raised concrete borders
Hello everyone. I have a number of raised borders in my garden, made of concrete block. The block has been waterproofed. The taller borders are about 4-5" deep and have a lot of concrete at the base, so not much contact with open soild. Others are shallower but with good contact with the underlying soild.
My question is this: what is the best compost/soil mix to go for given that I will be planting them quite full and with greedy plants? I would imagine lots of organic material? I want to avoid having to dig them out each year to re-energise them, almost as you would with potted plants...