Experts and BHG readers answer.
Can I plant my blue hydrangea in the backyard?
If you live in Zone 6 or warmer, your blue hydrangea should survive the winter when planted outdoors. In colder zones, the plant will probably die back to the ground over the winter and not bloom in the landscape. Plant it in spring anytime after your area no longer experiences freezing temperatures. In addition to preferring a site in partial shade, this shrub thrives in moist, well-drained soil rich in organic material, such as leaf mold and compost.
Grow the plant in acidic soil (pH 5-5.8) to keep the flower color blue. To acidify the soil around your hydrangea, work iron sulfate, a soil amendment, into the soil when preparing the planting hole. (If you apply the amendment directly to the soil's surface, it will take longer to work.) For pink blooms, maintain alkaline soil (pH 7-7.5). Winter protection depends on where your hydrangea is sited. If it's relatively protected from the elements, you won't need to do anything special. If your hydrangea is exposed to the elements, mulching around the base of the plant after the soil freezes can be helpful.