Climbing hydrangea is a stunning vine that will stop traffic when its white flowers pop out in early to mid-summer. Propagate climbing hydrangea by taking a softwood cutting in May or June. Although it can take some time, it's a hardy grower once its roots are established. Climbing hydrangea can eventually grow to heights of 60 to 80 feet, so be sure to plant it near a sturdy fence or wall to support the woody vines.
Use a pair of garden clippers or a sharp knife to cut a stem tip from a healthy climbing hydrangea. If the stem snaps crisply when you bend it, then it's at the perfect stage. Be sure the cutting has two or three pairs of leaves, and make the cut just beneath the lowest set.
Fill a planting tray with a mixture of half perlite and half commercial potting soil. Mist the tray with a spray bottle until the soil is damp clear through.
Use the eraser end of a pencil to poke a hole in the potting mixture. Strip the leaves from the lower half of the stem cutting, leaving only two upper leaves.
Dip the end of the cutting in rooting hormone, and plant it carefully in the potting mixture, being careful not to scrape off the rooting hormone. You can plant several cuttings in the planting tray. Plant them close together so they can share the hormones in the soil, but leave just enough distance so they don't touch.
Cut the remaining leaves in half horizontally. Smaller leaves will require less moisture and will take up less room in the planting tray.
Slide the planting tray into a clear plastic bag, and install a few small wooden stakes or a bent wire to keep the plastic from touching the cuttings.
Put the planting tray in a room in your house where the light is low and the temperature is about 70 to 75 degrees Fahrenheit. Check the soil often, and mist it lightly when the top inch is dry to the touch. Watch for the climbing hydrangea cuttings to root in about a month.
Transplant the climbing hydrangea seedlings to individual 4-inch pots, and put the pots where they will get morning sun. If the seedlings get long and leggy, then pinch them back to encourage bushy growth.
Water the seedlings when the top inch of soil is dry, but be careful not to invite root rot by watering excessively. The new climbing hydrangea will be ready to be planted outdoors in the spring, when the weather has warmed.