How to Move a #%!@ Large Shrub
Why the cursing in the title? Because to move this full-grown spirea took many back-breaking hours, that's why. So DON'T do what I did unless 
you really, really have to.
In this case, the rhododendron in back of this spirea died, a victim of our recent drought, and the best solution clearly was to move the spirea back into the corner to fill the empty spot. (The dead rhodo ready to be recycled is captured in the photo below.) All this work to move a plant less than 2 feet? Yeah, that's gardening - when you're persnickety about combining your plants so they'll look their best.
Staging the Move
And yes, staging is what's required.
- For 3 days before the big dig I soaked the soil around both the dead rhodo and the spirea.
- The rhodo is easily removed - mainly because I didn't have to keep it alive. Death is liberating that way.
- Next, to save the groundcover around the to-be-moved shrub. It's vinca minor and I know it's terribly invasive in some locations but for some reason in my neighborhood it's actually hard to keep alive. So I carefully lifted the clumps that would be destroyed in the shub removal and placed them in my trusty cement-mixing pans for safekeeping in shady spots til they're ready to be replanted.
- I began the spirea dig by creating a trench outside the root zone of the spirea through which I can slice under the root ball to free it. But boy, what a surprise the sheer mass of the shrub's root zone was - probably 5 feet across in every direction. So this baby wasn't going to be loosened easily.
- More soaking, waiting for the water to drain from the mostly clay soil and trying to dig again. You realize what all this soaking means, right? That it's much easier to dig up the plant but you're digging in MUD. Getting your clogs stuck in it. Getting filthy, in a wet way. Try it - you may like it!
- Panic set in as I began to wonder if I even CAN dig up a root mass this huge, no matter what clever tool I employ. I consulted (male) neighbors about the correct tool to use, none of whom were moved to volunteer to help me.
- Finally, seemingly against all odds, the root ball was severed sufficiently from the clay beneath it that it can be rocked loose and lifted. Aha!
- I dug the new planting hole, a mere 18 inches or so away from the original site, and slid the humongous shrub into it. With no help from neighbors, male or otherwise, I might add.
- I replaced the periwinkle around the spirea in its new position.
- I watered deeply once, then again in 2 days. Deeply in this case meant hand-watering with no nozzle, waiting while several gallons of water filled the whole root area.
The "After" Photo
Yes, I took a photo but honest-to-God, it looks just like the "Before" photo because the camera doesn't really highlight the crucial 18 inches by which the plant has been moved back into the corner. Nevermind. At least I know that after several hours of back-breaking labor, the damn spirea is in a better place than it was before. The real "after" will come next spring when this beauty's in full bloom, I suppose.
When to Do It
Late spring and summer are the riskiest times of the year to move anything because summer's the big killer - not winter - and plants moved during or just before summer heat will have a hard time surviving til autumn. So fall is the best time to make the move, sometime after Labor Day but early enough for the transplant victim to have a month to settle in before the ground freezes. In my Zone 7 garden that means that September and October are the prime times to plant or move shrubs.