steve stidham wrote:

I have read the continuous discussions on amending "hardpan" described as
clay soils. I live in PNW where hardpan is described as glacial till.

Fist of all, I think we must make it clear that'Hardpan' is not a
scientific term. It is a colloquial description of soil that is hard
and compacted. It means different things to different people in
different parts of the country.

It is
second only to asphalt in ease of digging. I have known it as clay my entire
life.

Whereas glacial till CAN have clay in it, even as a major component,
it is defined as being unsorted material of greatly varied sizes all
mised together..... tilled. Get it? When it forms rock it is called
tillite. Till is a description of the texture of various unsorted
particle sizes. It is not a type of material. Till can have any
kind of rocks or minerals present in it.

... Several speakers were making a
distinction between hardpan and clay layers in the soil. I got to speak with
a soil engineer and he described hardpan as a matrix of silt and rocks left
from the glacial period.

That could very well be true for your area, but as I pointed out
above, 'hardpan' is just a farmer term for dirt that is difficult to
plow.

He said it is even harder than clay when dry. Yet
with enough moisture it can soften and even wash away.

No doubt that this is probably the case.

... I think
clay is impervious to water, I have seen clay on beaches that does not
dissolve,

Maybe what you have seen on beaches is clay that is compacted to the
point that it is very nearly like rock.

If clay is impervious to water, how do you think potters mix it with
water to make it into pots? Water plus clay equals Mud!

A lot of us who have been stuck on clay road in the rain certain WISH
that clay did not absorb water.

The flat nature of the clay particle structure does lead to water
having a hard time moving through it. In fact highly compacted clays
can be pretty much impermeable. But water will move through clay to
some degree. And don't forget, clay soils are rarely if ever 100
percent clay. They are usually mixed with silt and sand and organic
matter to some degree and is always permeable by water to some degree.

hardpan on the other hand, will absorb water and soften. To test
if you will get a cistern, fill the hole to the top of the hardpan layer
with water. If it drains 15" of water in 12 hours an inch of rain is not
going to create a sump. To aid in digging you can add a foot of water to
the hole and return the next day to find 2-3" have softened and are easily
removed. It is slow but easier than using a 6' 14# digging bar. My personal
experience is limited to PNW glacial till if you really have clay and not
silt, the test above should disclose it.

No doubt that it is VERY hard to dig in glacial till. I feel for you.

Every gardener should do a soil drainage test ...no doubt. If your
soil doesn't drain, you must do something about it, absolutely.

On the other hand, if you actually have to dig through clay in your
yard, it will usually be in the form of rubbery mud once you are a
foot or so down into the ground. That is my experience.

Bob Bauer