Tool for planting seedlings in heavy clay rocky soil

Any recommendations on a tool to plant small seedling trees into heavy clay and rocky soil?
I have 100 fruit trees coming to plant in the spring.

I dont know how rocky 'rocky' is but I've used a one person earth auger 'gas powered' to plant a bunch of seedlings. My process was go along and dig all the holes where I wanted then go back and put the seedling in the hole and put the dirt back in the hole and pack down. This leaves a 8 inch diameter of very loose soil slightly below grade to help with watering. Hopefully that method would work in your soil.

This is the second real rock I found.  Will have to find a way to make it a home for lizards and small snakes to patrol my orchard.

hoedad or dibble bar are the common tools for planting barefoot seedlings

I hate auto correct
its not barefoot seedlings, it should be bare root seedlings
you will probably want to wear hard sole shoes while using dibble bar, some have side extension for using foot to push it in ground

This Fiskars all steel shovel has become one of my favorite tools. It makes digging in hard or rocky soil so much easier, and cuts through normal soil like butter.




It's got a wide foot step too which make it more comfortable to work with for longer periods of time.

I think one of the most important things about clay soil is not about the tools, but about making it diggable.  It is a pleasure to dig if it is not too wet and not too dry, so knowing that point is important.

Clay is best, even after planting, when it is not exposed to the sun....ever.  So thic organic mulch or wood chips, or where I have rodent issues, I use 3/4" rock around the base of a tree, so if they dig in that zone the rocks will fall on them and fill up their hole, discouraging them, and also show me where to put more rocks.

If starting with dry clay, wet down the area by soaking it with a hose, cover with a tarp and walk away for several hours or overnight.   Then go back when it's damp soil, and it digs easily.

If it's too wet in the spring, check the drainage in the area, which also may not be good for the tree roots.  Drain away too much ground water with a swale that can be blocked up at one end and used to hold water in a dryer time of year.

It also helps when you dig out the hole to pile the dirt on a tarp or a piece of plywood so you can easily put it all back into the hole.  

Other than that, your favorite shovel ought to do it.

Came across a heavy duty "Planting Bar" used in planting forests.  Called a Jim-Gem KBC Bar.  It is a very heavy duty spike that is 4 inches wide, 1 inch thick and 12 inches long.  I don't think I will wear this thing out.
I may still have problems with larger rocks but as long as I can get the pawpaw and Persimmon roots buried I will be happy.  I also have enough extra seedlings that I will grow some in pots as a back up.