You gotta define "topsoil"; it can mean pretty much anything. Parts of my garden is on yellow quarry sand from construction backfill and clean up fifty years ago, and some is on rocky clay undisturbed since the glaciers last came through here, and everything has a caliche component to boot. In the sand I use ridiculous amounts of horse manure and it works well here. Well over 50%. On top of the clay in raised beds I'd say there's less than a 20% organic content, again all from manure. Old manure. Some people here will tell you to aim for something like 10% organics and they will be right too. If you have several beds, experiment.

"I have horrible hard clay"

A thick layer of mulch to conserve moisture, renewed as often as needed might be all you need. If you have warm summers, plant okra and cut it off at ground level when fall arrives. . Its root system is huge and deep and leaves the clay full of tiny channels.

I dug holes for planting with a pickaxe, then covered the area with a thick layer of shredded trees ... renewed by spreading more compost on as needed. I have drip lines under the mulch for watering.

I can now fig anywhere in that area with a hand trowel.

definition of topsoil in my world: whatever the nursery scoops into my trailer when I say "garden mix". And my "horrible hard clay" doesn't have any nutrition to it. I have never seen a worm in 2 years of digging. My vegetables were crazy stunted last year, ex my zucchini plants which never got bigger around than a dinner plate. I added some compost and mulch and garden mix to the holes, but clearly not enough. If it rains on a hole, the water just sits there til it evaporates. The dirt also stinks when wet. BUT it's unlike any clay I have dealt with before, BC when it's dry it's like concrete to dig, but if you pick up a handful of just turned over dirt it crumbles! I just don't know what to do with it. I need to improve drainage AND give it some nutritional value

If you're putting tall-ish raised beds on top of the clay-crete, you're really ignoring the clay which is just what it deserves. You garden in the bed and ignore what's under it. As you go along, planting deep rooting things and adding materials that will leach down, the clay soil may improve, but you still ignore it. The bed is all that matters and the rest will follow along when it follows along.

The two main methods for improving clay are to add huge amounts of sand or to add huge amounts of organics. Both methods ignore the often-met fact that the clay may be deeper than a human can dig. I'd say go for the raised beds and pile them deep. If you do one at a time it will be easy.

The soil you will want to put into those raise beds would be something like about 45 percent sand, 45 percent clay, and about 10 percent organic matter. Do not simply ask for, or let anyone sell you, something as ephemerous (something that lasts only for a short time or does not really exist, or might be a figment of the imagination) as "topsoil".

How much horse manure to add would depend on the need of the soil mix, but it could be part of the needed organic matter. You should add the manure in a ratio of 3 parts vegetative waste to 1 part manure.

kimmq is kimmsr

Ellen, we have clay that is like concrete once it's dried out.

What we do to start a new raised bed is to break up the soil as deep as we can (during the 2 weeks we can dig either spring or after the rains start in Oct, Nov), top it with a good load of HM, water that in several times, then construct the beds with hardware cloth for gophers.

Start adding a good vege garden mix ( Most places in our area are certified organic, including the dump), water that in, add a few more inches, water in etc. Watering it in helps settle it so you don't have a huge drop over the winter rains.

I add a few inches of compost each year and till it in with my mini tiller.

I have had to re-do a couple of beds, and have been able to dig right down into the soil, even mid summer in these areas!

I've also found that areas that I've had my compost bins are really great and diggable!

I'm now moving my compost around and actually composting right on a fallow bed!

Nancy

If you have terrible clay, I recommend making friends with the local tree trimmers. Just have them keep dumping disease free trimmings until you have about a foot of it everywhere without of course burying the trunk of any tree or shrub.