*Correction* soild = soil...thought I had erased that 'd'...apologies for the typos...

Many peole with clay soils have found that adding organic matter, getting the humus level to 5 to 8 percent, is the best way to make that clay soil workable. This article, originally in Taunton Press' Kitchen Garden magazine, might be of some help. The author, Keith Baldwin, was at that time professor of soil science at North carolina State University.

Here is a link that might be useful: Improving clay soils

Cereal, I feel your pain. Organic matter is indeed the answer. Keep adding it, use organic mulches (compost, grass clippings etc.) and let the worms do the work all season.

Eventually you will get to a point where organic matter is high enough and porosity has developed from worms and roots that it may be better to stop digging it. It will take some years though.

You might be tempted to add sand, but be very careful. It can set up like concrete. Better to add silt (smaller than sand, bigger than clay) or a mixture. I found raised beds drained better in my wet spring weather, so I've added soil here and there, such as a load of silty sand from a boat ramp after a flood. It helps.

As you go along, try to avoid digging the clay when it's wet. It makes hard clods when you do that.

Clay is actually quite fertile, it just has difficult physical properties.

BTW tree roots can travel 50 or even 100 ft. They will keep coming.

Just layer compost materials on top of it & don't bother digging down in it. Much less work & your garden will grow! Plus it will save your shovel!

Gather materials as you have them available & layer where you want to garden. If that area is planted now, store in heavy duty contractor bags to build your layers after harvest. The heavy bags can be reused many times & last years outside. Grass clippings are best dried before storing in bags & are then browns.

Hope that helps!

These were some great responses, thank you all you have responded. I am going to take your guys advice and get back to work on it.

Thank you!

I've noticed that when I make a compost pile over an area of the garden, either over the winter or in spring, by summer the soil under it is moist and soft, whereas the bare ground next to it is compacted, dry and hard as rock. Not from walking on it, this is in a raised bed where there is no traffic. I think it's the combination of mulch keeping the moisture in, and worms coming after the compost pile. So corine's suggestions above really do work.

Whether adding sand to clay soils will result in a concrete type material, more likely adobe, depends on the type of clay and the amount of sand. Most Ag Schools research people will tell you that you need to add 45 percent sand by volume (Cornell will tell you 75 percent) to make some difference in clay soils (and you need to add 25 percent clay to sand) but then you still would not have a nutrient source that organic matter supplies.

Quite true...and most people are not going to want to haul in that much sand to get past the "concrete risk zone". Over the years probably 90% of my effort with my clay has been to increase organic matter, vs. 10% trying to change the texture of the mineral fraction. I supposed if I'd had a few more free trailer loads of that river silt it might be a different story ;-] But the point is: organic matter, organic matter, organic matter.

I'm fairly new at this, but I'm starting to develop a method. And I do have... clay dirt! I just don't know if much of this applies to zone 9.

Compost Pile:
Pile up the leaves in the fall. Mix in a pickup truck of fresh manure in the spring. Let the pile rot all summer. Move it to the garden and turn it under in the fall.

Garden:
In the fall, after mixing in the past season's compost pile, add a thin layer (maybe 6 inches) of "fresh" fall leaves on top of the ground. Let it start to decompose under the winter snow (zone 5 here). Come spring, turn the fresh leaves into the ground as well, they are "gone" by July. Mulch after spring planting with leftover bail of straw from someone's fall/Halloween party or church's Christmas manger setup.

This is really only my second season, and the ground is no where near as compacted as it was when I started. I expect soil to be even better next year. Oh, yea, add usual kitchen scraps (but this is a small volume of my pile).

Claydirt, there is no good reason to pile leaves up in the fall and wait until spring to add a Nitrogen (manure) source. Mix those leaves 3 parts leaves to 1 part manure (or some other Nitrogen source) in the fall and by spring that compost will be ready to use.
There is no good reason to turn leaves put down on your soil as mulch in the fall into the soil in the spring since they do make a very good mulch for the garden nost of the summer.
Adding organic matter to any soil is the single most effective way to make that soil into something that can grow good healthy plants.