You won't have a bathtub effect if you backfill with native soil from the hole. Don't be gentle backfilling a planting hole. Don't add compost or anything like that. If you have a well amended planting hole- then any dense clay etc. around the hole acts to hold water in like a bathtub. If it's the same soil right up to the roots- then there's no difference and no bathtub.

Soak the bare-root tree for an hour or 2 before planting. Dig the hole wider than needed and backfill with soil from the hole. Step on it to compact it a bit. When it's full, step on it a bit more and water-water-water to reduce transplant shock, and to further settle the soil (you don't want any air gaps!)

Add compost etc. on top of that and it will work it's way into the soil and leach yummy nutrients in.

Think about how saplings grow. They freaking astound me- they can bust through asphalt, push down walls, and the taproot will find its way through nasty gravel. I cannot think of a better symbol of strength or persistence (well- them and salmon). Let it do the rest of the work for you in punching through deeper subsoil if it needs to.

Well, that's my opinion. I planted a mess of trees in shallow soil with almost pure sand under them (the lot was scraped before building :( I was worried about soil depth- but I had cheap saplings and let them go. They're doing great after 4 years.

I live in Southern Utah and have the same hard layer a couple of feet below the surface like you do. How's the drainage on your soil? Have you tried filling up the hole you dug with water and seeing if it drains? I took some tips from Star Nursery, I'll share them with you:

DIG A BIG HOLE. Dig your hole at least two to three times as wide as the plants rootball. You may want to dig deeper than the root ball, but then you will need to prevent soil compression. If the plant settles or sinks after planting, it is likely that the crown will become exposed to perpetually moist soil and develop disease or rot. Use granite rock beneath your plants rootball if necessary to prevent settling. (This tip is the most important!): The wider the hole, the better you can expect the plant to do. Fruit and nut trees in particular will benefit from a wide hole. (I always dig a 'cereal bowl' shaped hole. My fruit trees love it!)

CHECK THE DRAINAGE. Fill the hole with water. If the soil drains within 45 minutes, proceed, if not fill the hole again. If the soil drains within 3 hours proceed. Often planting the root system above the mean soil line will compensate for slow drainage. Still not draining? Dig a chimney tunnel at the base of the hole to break through to a more porous level. If you encounter non-draining hardpan (caliche), try breaking it with a "caliche bar" or mattock. If you canÂt get the hole to drain before you fill it in, it wonÂt drain afterwards, either!

MAKE A BACKFILL MIXTURE. Mix your reserved native soil with amendments (I think your fully composted stuff or manure would be best, but NOT the wood chips, they'll suck nitrogen from the soil around your tree as its trying to establish) at a ratio of two parts native soil to one part amendment. (The 2/3 to 1/3 ratio is important. I wanted to give my tree MORE good stuff, but if you do, the tree will grow expecting that soil and when it finally hits the native soil - BAM! Shock!)

STARTER FERTILIZER. Do not add high nitrogen fertilizers when planting. A good starter fertilizer will provide good levels of phosphorous and potassium, while providing a minimum of nitrogen.

BACKFILL. If the hole is deeper than the root ball, add rock at the bottom of the hole to a point sufficient to support the root ball equal to the surrounding surface. Rock will not compress and so prevents the roots from later sinking and causing potential disease and suffocation problems. Add mulch into the rock to assist root development later.

SET THE PLANT IN PLACE. Make sure the hole has been pre-moistened. Set the root ball into the hole. Fill the hole with amended soil, tamping lightly as you go. Bring soil level even with tip of the root ball. DO NOT BURY THE ROOT BALL!

Hope that helps - Happy Planting!

This link provides good, solid tree planting information. Note that they do say "fertilizer" is usually not needed with a newly planted tree, especially phosphorus and potash.

Here is a link that might be useful: Tree Planting