go to a good nursery ... and find an equivalently sized plant.. and study the pot or the ball and burlap for how big a professional would do it ...

that will clue you in to the MINIMUM size ... a little bigger never hurt ...

before you go ... snip off a piece of yours from the rear .. and have the nurseryman ID the plant for you ... and then ask him what it is worth ... how fast it grows.. etc ...

then go back home.. and consider the SCOPE of what you are thinking about doing ... versus the cost of what you are doing ....

per 6 foot plant.. i could easily see 4 to 6 hours of intense extreme physical labor ... if you dig a 2 to 3 foot rootball .. will you be able to drag that 100 to 200 pounds of soil plus plant across your property ... etc ...

again.. depending on the plant.. you may be able to invest 100 to 200 dollars in some decent plants for the back .. and just chainsaw these down to the ground ... and get the front of your house back ...

on top of all that ... larger.. older plants.. have a much harder time dealing with the stress of moving them.. short of hiring big guys with big machines to do it right ...

BTW... make sure you know where all your buried utilities are...

its the old cost benefit analysis .... good luck with that .. lol

when all is said and done... there is a big difference between what CAN BE DONE... and what SHOULD BE DONE .... yes its possible.. but should you do it... too much work.. and failure rate is too high ...

i vote no ... be done with them ...

good luck

ken

"It's coverage above ground-so for a 6 foot evergreen, expect to dig the same, 6 feet down and a few feet out?"

No, the root system of trees and shrubs do not mirror the above ground portion of the plant. One of those giant trees that they move on TV where they move it over a period of two to three years and use a semi truck with police escorts isn't even 6 feet deep!

Here's a rough guide to use:
For trunk diameter below 1/2", multiply the diameter by 20 to get approximate rootball diameter.
For trunk diameter between 1/2" and 1", multiply the diameter by 18 to get approximate rootball diameter.
For trunk diameter between 1" and 1-1/2", multiply the diameter by 16 to get approximate rootball diameter.
For trunk diameter between 1-1/2" and 2-1/2", multiply the diameter by 14 to get approximate rootball diameter.
For trunk diameter between 2-1/2" and 4", multiply the diameter by 12 to get approximate rootball diameter.

Here are guidelines for rootball depth:

For a rootball with a diameter of 1', depth should be approximately 8".
For a rootball with a diameter of 2', depth should be approximately 1'.
For a rootball with a diameter of 3', depth should be approximately 15".
For a rootball with a diameter of 4', depth should be approximately 18".

Here is a link that might be useful: Generic Rootball Size Guide

And don't prune the top to 'mirror' the root ball! That will surely put an end to this project. The foliage is where your shrubs will get the energy to make new roots.