Climbing hydrangea, known botanically as Hydrangea anomala petiolaris, is a true climbing vine that will attach to nearly any wall surface or structure it comes into contact with, according to the United States National Arboretum. Hardy in USDA zones 4 through 7 and known to be somewhat slow to grow and mature, once established it will produce large white flower heads from June through August each year. Beyond being well-established in the landscape, weather and environmental conditions contribute most to bloom performance. Protecting buds from freezing, proper sunlight and nutrition along with favorable moisture conditions will help to spur bloom.
Protect the tender flower buds from late spring frosts by covering the shrub with a canvas or plastic tarp when cold temperatures below 40 degrees Fahrenheit are predicted. Cover in the early evening just after sunset and uncover in the morning once the sun is up in the sky and the frost has dissipated.
Feed your hydrangea in the spring each year with a slow-release, complete granular fertilizer formulation with a guaranteed analysis of 15-15-15 or 10-10-10. Cast the fertilizer around the entire root zone and water in well. Do not dig the fertilizer into the soil, as this may disturb the shallow surface roots. Apply according to the product label dosing directions, but do not apply more than 2 lbs. of fertilizer for every 100 square feet of planting.
Water your climbing hydrangea deeply once every five to 10 days when there has been no rain. Keep the soil moist, but not soaking wet, at all times. Increase watering in the heat of summer and during peak growth and taper off in the winter or when rain is plentiful.
Provide partial daily sun to lightly filtered shade conditions. Climbing hydrangea can tolerate more shade than most other hydrangea species; however, deep, persistent shade with no sun can diminish bloom.