Dividing Hydrangeas

Hydrangeas will inevitably outgrow their surroundings--or crowd out other plants in the garden. When this happens, or when you decide it's time to split up a nice specimen to allow for another equally spectacular bush, follow these steps on dividing hydrangeas.

Step 1: Divide While Still Dormant

The best times to divide hydrangeas are in the fall when the leaves have fallen and the bushes are ready to go dormant, or in early spring before new growth begins. Choose the appropriate time to separate hydrangeas and get to work.

TIP: Our expert gardening advisor, Rachel Klein suggests, "One day before you plan to split the hydrangea, water it thoroughly (without soaking)."

Step 2: Tie Up the Hydrangea

Tie the limbs of the hydrangea with twine or rope into sections for dividing. This keeps the shrub contained for easy transport and helps to expose the stem for easier digging.

Step 3: Dig Up the Rootball

Dig around the perimeter of the hydrangea bush about 2 feet from the main stem, using a shovel to make sharp and deep cuts. Work to loosen the roots from the soil as much as possible without severing them. Remove the rootball. Caution: mature hydrangeas can seem as if they weigh a ton! Some gardeners have reported rootballs as hard as cast iron. While this may be a slight exaggeration, the rootball of an old established plant is very heavy. This may necessitate even tougher measures to dig it out of the ground, including using a pick and an ax.

Step 4: Divide the Rootball

Now that the rootball is out of the ground, don’t despair at its huge size and weight. In fact, the depth and width of the roots are good indications of the health of the hydrangeas. Use the shovel again, possibly with the help of a pitchfork, to divide the rootball into the number of desired sections. First, align the blade of your shovel into the middle of the root ball, applying pressure to sever it into two individual shrubs. From there, divide further if need be. For most large hydrangea bushes, this will be 2 to 4 sections, although particularly large ones may be divided successfully into 5 or more smaller clumps.

Step 5: Plant in the New Location

Once the hydrangeas have been divided, it’s time to plant them in the ground in their new home. The best time to plant hydrangea sections is when the skies are overcast, although with a little care they can be transplanted any time of day. Fill the hole partially with water and loosen the soil so that the roots can penetrate easily. Add a good mixture of topsoil and manure to help get the new plants started.

TIP: Rachel adds, "Loosen the root ball to expose more of the root system. Place your shrub in the hole and make sure the new depth matches the depth of the original hole. Your hydrangea will have soil marks on its stem from the previous soil line. Do not plant it deeper than these lines."

Step 6: Mulch And Water

Add mulch around the newly-divided and transplanted hydrangeas and water deeply for several hours using a slow-drip method. Be aware that the hydrangeas will most likely droop at first, but they’ll perk up after a few days. Keep watering throughout the summer, as these new plants need to get their roots deep into the ground and need lots of nourishment.

Many varieties of the mophead and lacecap hydrangeas can be successfully divided, but one appears to be particularly receptive to this type of division. That is the Nikko Blue, one of the most popular hydrangeas grown by home gardeners. This variety of hydrangea grows fast and needs a lot of room, so make sure to plant it in an area where it will have plenty of room to spread out.

After dividing, replanting, mulching and watering, just keep a vigilant eye on the plants during the summer and watch these new hydrangeas begin to take off. This method of dividing the plants can be used on any mature hydrangea plant in succeeding years--so there can always be new hydrangeas in the garden.