I have lifted a number of slabs in the garden to create more space for plants but beneath the old slabs the earth is covered in concrete / cement powder (looks like grey sand). I don't think I want to grow any veg in this but I am unsure of how to get rid of it and how best to prepare the ground for planting. Will it even be safe to eat veg grown in this earth if I don't get it all?
I was thinking about removing as much as possible and digging manure in then putting down a cardboard mulch with compost on top.
all advice very welcome!
You would have to remove as much of the material as possible that was used to bed your slabs on and any hardcore as well. The ground will be very compacted and will have to be dug over thoroughly adding compost as you go.
Perhaps you could build a raised bed on the area after, with some good top soil and compost, to give the plants better growing conditions.
I've removed as much of the grey stuff as possible and dug over the earth a bit to remove some old tree roots. Thankfully there isn't any hardcore (the previous owners have cut corners on every piece of DIY I've found so far) but the ground is very compacted as you said. I'm going to get compost at the weekend and dig it over properly then.
depending on what you are going to grow on that patch, if just veggies than save your money and dig in well rotted manure, you can tell if it is well rotted as it shouldnt smell, hope this helps