Hello. I currently have four mature (roughly 8 feet tall) Siberian Pea Trees in my yard. Unfortunately, I think they were originally planted to close together. Regardless, I was curious how difficult it is to dig up the root system, and possibly separate the roots somewhat to turn 4 into 8 and then transplant slightly further apart. They are currently an excellent wind break, but again, are simply too close together.
Siberian Pea Trees
Certified GKH Gardening Expert
I would not transplant them now until fall when weather is cool. Transplanting in the heat of summer causes unnecessary stress to plants. When you do dig them up, you can remove the soil from the roots and see if it is possible to divide the plants safely. These articles may help