Planting on clay

Hello, I have just discovered this site through the wonderful plant lists when I was trying to find a picture of what a new plant will look like when it's grown up.
I have a question.
Last year we dug a natural pond-to-be, and when we finish it, we plan to put some decking around one side of it, backed by trees and shrubs.
However - we made the mistake of having the earth - 90% clay - spread around the edge of the pond. It covers a larger area than the decking will and is about 1 - 1 1/2 feet deep. Under it is the original topsoil.
What I need to know, is this:
Is it better to scrape off the clay and plant into the original soil, or can we plant things into the clay and they'll find their own way to the good stuff?
If it matters, we are in the north edge of SW England, so by turns, waterlogged and dried out!
Cheers
Anji

Are you planning to plant regular plants or bog plants? If you're planning to do regular sorts of garden plants, you're probably better off scraping off the clay. Your clay is probably worse than most gardens, even people who have heavy clay soil it's probably not 90% clay like yours so I think most plants are not going to like that at all. If you want to do bog plants on the other hand then maybe it would be OK, but you'd probably have to make some efforts to keep it boggy during the times when it would normally be dried out.

Thanks for that.
We're planning on ordinary trees and shrubs, as a backdrop and some protection for the decking, so they wouldn't be near enough to the pond to be in boggy ground. I guess we start scraping!
Cheers
Anji

A lot of our native soil is very 'clay'ish ... if you shake the dirt off the roots when you drop em in the ground, they will dig through the clay.... if you don't then you will end up making a clay bowl that will hold water and they will drown

I don't think your native soil is 90% clay though, that's special stuff that you buy to make ponds with. I think planting stuff in soil that's 90% clay is going to cause problems unless it's bog plants.

We have a lot of clay in the ground where I live. I just amend the soil with good black dirt and compost. The clay helps retain some of the water during dry spells and the compost will help break down the clay so you end up with something better in the end. If you've got a fairly big section, you can till everything together to make it easy to plant.

Hurry up and get rid of the clay if you want to save that dirt. If you bury good dirt under it, the good dirt will suffocate and eventually die turning into bad dirt as well. Good dirt needs organic matter, aeration, and moisture. Burying it under 1 1/2 feet of clay you've eliminated aeration, and clay resists moisture. So, the question isn't if the plants will seek out the good dirt under the clay it's how long will it be good before it turns to junk.

You have several options. The clay you have on top is probably junk since it came from below and probably has very little organic matter, beneficial bacteria, nutrients, etc and the dirt below will become junk as well and then you'll have all worseless dirt. So, you can convert the clay on top to good stuff by adding plenty of compost each and every year, or growing green manure/sacrificial crops and slowly over the years you'll start to make headway and convert it to good stuff. It's the option with the least amount of work, but will take easily the most amount of years. Or you can remove the clay on top to expose the good dirt again, move it out of the way, put the bad clay down first and the good dirt on top and add some compost/organic matter to it repair the damage done. That's the most amount of work, but you'll most likely have repaired the damage done in a year or two. Last, purchase good dirt and cover the clay with it. You'll need to go deep for drainage reasons.

Oops, I just noticed you said "Last Year" you did this. I wouldn't put money on the original topsoil burried under the 1 1/2 feet of clay being worth much anymore. You'll have to go with either trying to convert what you have there now to good stuff by adding lots of compost over the years, or shovel some off and lay down some good dirt.

Dig the hole twice the size as the plants bucket, mix clay with "Clay Buster" & a root stimulator.
Let it grow.

I would try get rid of the clay due to your area in SW England, the reason I am saying this' because you have now changed the ground level with CLAY and this contains so much moisture, stays colder for longer and as you said, bakes hard in the summer, you could give yourself even more problems in a few years time, it COULD cause water to shed too close to your home, it will cause your decking to be constantly damp as it will act like a sponge, we dont have the kind of wood and wood treatment they do in USA, then there are the problems you will have while trying to landscape your garden, even If you add tons of compost or manures to improve your clay condition, you have a second layer of clay already burried under your GOOD soil, this effect is like a sandwage of clay, proberbly only about a foot and half of good soil in the middle, then DEEP clay under that, as you proberbly know, in your area, lots of big homes and estates built huge ponds, because of the soil being such a high density of clay, therefore they did not need the modern liners, they just flattened and treaded the clay into the pond shape, AND they very rarely leeked, some still great after hundred years, that alone will tell you the amount of water this soil can contain, I am not trying to scare you, but perhaps you could pay for a soil annalyst to give you proper readings of the water content in your area, but then again, that could cost more than getting the clay from the pool construction removed, I hope this gives you some insite to the problems that MAY occur in later years and just want you to really think about any quick fixes, it could cost you your home or trouble for your neighbours property if tons of water shed in the wrong direction, especialy as we have had such heavy flooding the past few years, hope this gives you food for thought, good luck anyway, hope all turns out well for you in the end and you have the garden you are trying so hard to create, WeeNel, Scotland.