According to Clemson University, root pruning should be done at least 6 months prior to transplanting and only after the leaves have fallen in fall (October) or before budbreak in spring (March). To do so now would unnecessarily stress the shrubs and can cause damage, perhaps irreparable. Can the transplant be done early next season, so you could wait to root prune this fall?

It is not absolutely necessary to root prune before transplanting shrubs, but it does decrease transplant shock. This is also limited if you wait until the shrubs are dormant. Fall is an ideal time to do this, as is early spring. Just make sure you take a sufficiently large root ball. And water appropriately after replanting.

Here is a link that might be useful: Clemson - transplanting shrubs

pshaw ...

IF YOU ROOT PRUNE.. YOU WILL SEVERELY STRESS THE PLANT....

why do that ... and then stress it again in 2 months.. you already suspect such ....

just root prune it once.. when you dig it up and move it ...

otherwise.. you should have root pruned half 2 years ago.. the other half last year.. and then moved it this year ...

you know.. i am a MG.... i took the EIGHT WEEK COURSE ... and after 40 years of gardening.. do NOT feel myself qualified to give advise AS A MG ... that whole program is really irritating me.. as we get posts from peeps who get horrible info from basically untrained peeps ... but i digress ...

THE MOST IMPORTANT ISSUE ... imho .. is timing of the move.. in my z5 .. that is october ... warmish days.. and cool nights .... call your local extension office if you need ...

get them ready for the move by insuring they are well watered between now and then [i am in 9 weeks of drought, so i would trickle water them extremely well for the next two months .. but not drown them] ....

when the time comes.. dig the new hole ... dig the plant.. move it over there ... plant it PROPERLY .. water it PROPERLY.. then mulch it PROPERLY .... ask if you dont know what PROPER is ... for each of the above ....

forget about root pruning... too much stress ....

ken

Do not know most recent findings or thinking by him or anyone else on root pruning prior to transplanting but as recently as the 1991 revised edition of Establishment and Maintenance of Landscape Plants production methods trailblazer Carl E. Whitcomb had concluded that root pruning was probably best left in the realm of the theoretical - multiple trials having failed to demonstrate a marked benefit. The root-pruned specimen typically would have to endure two rounds of root-cutting rather than one - unless the new roots grown out from the cut ends the first time are not themselves again cut when the plant is lifted and moved to the new site.

Why did she suggest moving the shrubs? Is it to get more/less sun, better landscaping effect, etc? Unless the shrubs have been there just a year or so, the thought of moving those makes me tired. The sambucus, in particular, will have a ginormous root system in maybe 3 years.

I'm suggeting an alternative might be just planting new ones. The fall of the year, the plants can be had for cheap. Then when the new ones are doing ok, you could cut down the old ones (heartbreaking, but less work.)

Replacements of all could probably be fairly easily started from hardwood cuttings taken from the existing specimens before they were removed and discarded.

Thank you all for your suggestions. The main reason for the advice to move the bushes was due to their initial installation. We hired a professional landscaper to develop a plan and she did create an initial plan. However, after that she basically disappeared, refused to answer our phone messages, and apparently stopped working as a landscape professional for some time.

In addition, the nursery that was providing the plants didn't have some of the ones the plan called for or didn't like some of her choices. Since she wasn't available, and since we had no gardening or landscape experience, we pretty much trusted the nursery to do all the plantings.

Now some of plantings aren't working out in terms of color and size - some of the shrubs in particular have overpowered their area. Ironically, where we wanted large bushes to screen out our neighbors, the lilacs and cherry laurels that were planted haven't done the job. I posted pictures below to illustrate.

On the left, behind the lavender, there is a variegated redtwig dogwood that is overpowering the korean spice viburnum behind it, the eryngium yuccafolium in front of it, and the echinacea beside it. We were thinking butterfly bushes might work better here.
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Here is the same shrub from the back. The viburnum is pressed between the redtwig dogwood and the pyracantha on the right hand side. This composition of this whole planting area seems off to us, with tall things in the front and short things behind, etc. but we are unsure what to do with it.
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Here is the side where we wanted a screen. You can see the neighbor's propane tank and back porch. The master gardener suggested sambucus here:
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Here is the sambucus, which has completely obscured the view out of this window. We love them and they are beautiful, but we would like to see the river as well:
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If you have any further comments, I am always opening to new ideas.

Thanks!

I can see some crowding developing in the future, but for the moment I see lots of uncovered mulch and some plants growing close together or even sharing the same space without serious conflict. If you are expecting to have a "tombstone planting" consisting of compact, crisp shapes with plenty of empty space around each then you have to a large extent ended up with the wrong kinds of plants. The existing planting is going to produce an informal effect with lots of softness and naturalism. If anything, I would add more plants to get better fill and more drifting of kinds, there is too much use of single specimens (the solitary dwarf gaillardia at the corner is particularly static and inconsistent with the appearance of the rest of the plants in the same view).

The redtwig dogwood is big enough that you could start cutting a few stems down low at the end of winter every few years or so to keep it renewing from the bottom. Selecting taller stems that you see as too close to a neighboring plant could be a way to deal with the "pressing" you are concerned about.

Shrubs you can't stand where they are should be moved when leafless, unless any are evergreen of course. Just dig them up and re-plant in the new spots. Getting as many roots as possible should be the goal instead of fiddling with root-pruning, which is supposed to be a way to get more roots but it starts with cutting roots off. Then, as I mentioned earlier unless done with special care the roots are again cut off when lifting later, defeating the purpose.

bboy:
Thank you for your insightful comments. We are actually happy with the informal effect - it just that we didn't know how informal this area should look or how close the plants should be. Thank you for your reassurance on that score. Also, your technique of cutting some stems at the end of winter could be the solution to that one troublesome area we are grappling with.

I have to smile about the dwarf gaillardia. We were told to plant one there and then one on the other side of it because "if you plant something on one side, you plant the same thing on the other." We were also told that it would help pull in the colors from the kniphofia and the penstemons on the other side of the path. It does look rather lonely there, however.

I have included a picture below that shows the other side of the path - the other patch of gaillardia is in front of the penstemons, which unfortunately is not in this picture.

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Some of the area that is bare formerly belonged to lavender bushes that died this spring and will be replanted. We are also planning to plant some tickseed coreopsis in front of the lavenders as well. Now that we know we can incorporate more plants, we can begin to look for other candidates that would work well here.