Planting in a garden with buried rubble

Newbie in need of urgent help. Our house builders buried construction rubble in the back yard and I stupidly agreed to a quick fix of dropping approx 12cm topsoil which was enough to get a lawn going (this was 12 years ago). I'm now attempting to plant Hydrangeas, Lavender and Lillies in a border and have dug 30cm wide x 40cm deep 'potholes' using an SDS Hammer Drill. Spades are useless as there's all sorts of nastiness down there e.g. tarmac, concrete, bricks and sand (no soil apart from the initial 12cm top layer).

I've bought bags of Topsoil, compost, farmyard manure (all from Wickes) as well as Chicken Manure Pellets (Homebase) and was thinking of creating my own general all-purpose mix for not just the above potholes but also for raised beds, planters, hanging baskets and future indoor plants.

Question 1: I've been mixing the topsoil and compost in equal measure (50/50) and throwing in a handful of pellets and manure as I mix. Is this OK or should I change the ratios? I don't wish to add anything and simply use what I already have so please advise accordingly

Question 2: I've planted a few plants already by lining the bottom of the potholes with approx 2-3cm manure before adding the above potting mix? Not sure why I did that - I guess I may have read it somewhere. Is this process OK?

Question 3: What's the likelihood any plant will survive in 'potholes' surrounded by rubble? My logic is: if they can survive in plastic pots, they can survive in a rubble-lined hole!

 

Survive but not thrive probably sums it up. Lavender should be alright, but hydrangeas need a fair bit of moisture to do well and with all that rubbish in it your soil is probably free draining and on the dry side. If you look round GC you will see a lot of questions about hydrangeas struggling this year.
Best thing to do is get some good gloves, a skip and a pick axe and remove as much of the rubbish as you can. Failing that raised beds would be the way to go.

 

Thanks mate - any suggestions on the 'mix'?

 

Hi @crapgloves I'd agree with @NigelJ that the only real solution is getting out as much rubble as possible. You can mix compost with topsoil, but really what you need is just a lot more soil in there - compost improves things if the soil is poor, but if you get good topsoil it shouldn't be needed. As for the manure, well rotted manure is lovely stuff, but if it is 'fresh' then a layer can burn off tender roots. I'd prefer to mix it into the soil.

 

Not necessarily! Often a lot of lime in rubble, lots of plants hate lime.

 

My main bed here has a small depth of soil atop rock. This is the island norm. No rabbits as they cannot burrow ( hares instead) and no burials. When my kind neighbours buried my dog here they were chipping at rock.

I am amazed at how well things grow. Beans and peas, herbs, flowers. No additions by me. The lupins could take over the world.