Question: I want to transplant an old-growth hydrangea that's about 5 feet in diameter to a new location. What is the best way to dig it up, and what time of the year should I do it? I will rent a backhoe to dig it up if necessary.
Answer: Every time someone asks me about the best time to move a mature shrub, my answer is “never.” However, I know that there are many different reasons why someone would have to relocate a mature shrub, and I have done it myself many times over the years. I've managed to have a very good rate of success. The trick, it seems, is a combination of proper handling techniques and after-care.
Let's start with a less-important concern before moving on to those two: The timing. While certain shrubs much prefer to be transplanted at a particular time of year, hydrangeas do not. As long as you avoid the heat of summer, anytime during the growing season would be fine. That being said, if you choose to move it in the spring, you'll need to be more diligent about watering than if you were to wait until fall. Fall transplants often receive more regular rainfall and therefore tend to require less artificial irrigation. So, if you are willing to turn the hose on every few days, go ahead and move it this spring, but if you want Mother Nature to handle some, if not all, of the watering chores, wait until the fall.
Regardless of the timing of the transplanting process, the proper handling of a mature shrub is a must. Dig a root ball (I much prefer careful hand-digging to backhoe digging on a shrub of this size. We are not talking about a massive tree or shrub specimen here.) The root ball should be large enough to extend a foot or more out past the drip-line of the shrub (the outermost tips of the branches).
Hydrangeas do not form a tap root, so the root ball does not have to be super deep, but it should extend down as deeply as you can handle. The width of the root ball, in this case, is more important than the depth because of the fine, fibrous roots of the hydrangea. Work carefully to keep the soil intact around the roots. You don't want the root ball to “crack.”
Once the root mass has been dug, lay a tarp down next to the hole and, using a helper or two, shimmy the tarp underneath the root ball. If you can't do this, carefully lift the root ball out of the hole and place it on the tarp, again being careful not to “crack” it. Once the shrub is safely out of its old home, drag the tarp to the new location.
When preparing the new planting site, dig the hole about twice as wide as the root ball, but no deeper. Position the hydrangea into the hole and make sure it will be planted to the exact same depth as it was in its previous location. Planting too deep is the kiss of death for trees and shrubs.
Backfill the hole with the same soil that was excavated from it, breaking up lumps and tamping out air pockets as you go. Adding compost or other soil amendments to the backfill is no longer recommended due to the creation of a “good soil pocket” in which the roots are likely to circle. Refrain from fertilizing until a year after planting, as newly developing feeder roots are sensitive to fertilizer burn. Pruning should also be delayed for six months to a year.
Once the shrub is settled, water it thoroughly and continue to do so for a year or more after transplanting if ample rainfall doesn't occur. Deep, twice-weekly irrigation is far better than shallow, daily waterings.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
