How does one move a large overgrown shrub? Very carefully and with a lot of sweat. I should mention that summer is not the time to move almost any plant. September and October are the best months to move stuff; spring is second best.
Moving a large shrub is definitely a two-person job; three strong backs are even better. The first issue is finding the new location for the shrub. You really need to try to give it about the same light conditions it has now. It is overgrown in part because it is happy with the light it receives; full sun or partial sun. It is best to dig most of the new hole before you begin working on the existing site.
The success for moving a shrub is directly a function of how big of a root ball you can handle. The root system of your large shrub goes out at least to its greatest width and sometimes even further.
The name of this game is to try to bring along as much of that root system as you physically can. In most cases, your minimum size for any possible success is 3 to 4 feet in diameter and a foot to 2 feet in depth. Most shrubs have a fairly shallow root system, with the majority of the mass in the top 6 inches. At the same time, there are roots that go deeper that are good to save if you can.
You will thoroughly water the target shrub the night before you plan to make your move so the soil around the roots is damp, not dry. Dig out at least 1 foot from the outside edge of the root ball and preferably 2 feet out. You need room to maneuver when you start moving the plant.
The root ball has to be free around and underneath, because you will need to place a heavy piece of canvas or some other material under the root ball. That is how you will move the sucker, so a lot of overlap of canvas is good.
Now you move the plant to its new location trying very hard not to lose too much dirt from the roots. This is hard work.
Make sure the new hole allows the shrub to be planted at the same level of soil as it had originally. Add a few shovels of compost, water the hole, and plant the shrub. Add a 3-inch layer of organic mulch and plan on watering that new transplant almost every sunny day for a few weeks.
If you can still move your arms, have a beer for me.