Hydrangeas will inevitably outgrow their surroundings or crowd out other plants in the garden. Whether you want to divide your hydrangeas due to overgrowth or because you simply want to split up a nice specimen to allow for another, equally spectacular bush, follow these steps for doing so properly.
While many varieties of the mophead and lacecap hydrangeas can be successfully divided, the Nikko Blue, one of the most popular hydrangeas grown by home gardeners, seems especially receptive to this technique of division and transplantation. This variety of hydrangea grows fast and needs a lot of space, so make sure to plant it in an area where it will have plenty of room to spread out.
Step 1 - Divide While Dormant
The best two times to divide hydrangeas are in the fall when the leaves have fallen and the bushes are ready to go dormant, or in the early spring before new growth begins. Choose the appropriate time to separate hydrangeas and get to work.
"One day before you plan to split the hydrangea, water it thoroughly without soaking," suggests Rachel Klein, our expert gardening adviser.
Step 2 - Tie Up the Hydrangea
Tie the limbs of the hydrangea with twine or rope into sections for dividing. This serves two purposes: to keep the shrub contained for easy transport and to expose the stem for convenient access when digging.
Step 3 - Dig Up the Root Ball
Dig around the perimeter of the hydrangea bush about two 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 while being careful not sever them. Remove the root ball or the primary mass of roots beneath the plant.
Be careful! Mature hydrangeas can be particularly heavy. Some gardeners have reported root balls as hard as cast iron. While this may be a slight exaggeration, the root ball of an established plant will be heavy and thick, so properly removing a mature root ball may require tougher measures like using a pick and an ax.
If you know ahead of time that you’ll be working with an older plant, plan accordingly and bring some heavy duty tools to excavate that mass of roots.
Step 4 - Divide the Root Ball
Now that the root ball 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 indicators of the health of the hydrangeas. Use the shovel again, possibly with the help of a pitchfork, to divide the root ball into the number of desired sections.
First, align the blade of your shovel into the middle of the root ball, and then apply pressure to sever it into two individual shrubs of approximately equal size. From there, divide further if need be. For most large hydrangea bushes, this will be two or four sections, although particularly large ones may be divided successfully into five or more smaller clumps. Keep around 12 eyes per clumps as a guide.
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.
"Loosen the root ball to expose more of the root system," adds gardening expert Rachel Klein. "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 recently divided and transplanted hydrangeas and water deeply for several hours using a slow-drip method. Be aware 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 to get lots of nourishment.
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.