Hydrangeas like well-drained humus soil containing organic material like molded leaves or compost. You can use leaf mold or compost that you created yourself or you can purchase organic material from a nursery or garden center. Adding organic material to the soil provides health benefits to all hydrangea varieties, while pink or blue blooms of the Lacecap and Mophead varieties of hydrangea can be controlled by chemicals found in the soil. Prepare the soil for planting in the fall, early summer or late spring after danger of frost.
Get the soil tested if you desire to control the bloom color of Lacecap or Mophead varieties of hydrangea. Let the testing agency know that you are planting hydrangeas and want to know whether the soil contains aluminum and what the pH level is. Contact your state or county cooperative extension office for assistance in locating a soil testing agency near you. A pH level between 6.6 and 7.3 is considered normal. Higher-than-normal numbers indicate more alkaline soil while lower numbers indicate acidic soil. Shades of blue in Lacecap or Mophead hydrangeas come from acidic soil of around 5.5. Shades of pink come from alkaline or neutral soils.
Choose a location where the plant will get morning sun and afternoon shade. Unless you plan to prune the plant regularly to maintain its size, you should plant hydrangea in a location where it can expand. That means an open area of at least 5 feet in diameter. Hydrangea can grow wider than 5 feet if never pruned or if blooms are never cut.
Dig a hole according to the plant's tag, or two to three times as wide and one and half to two times as deep as the hydrangea's root ball. Digging deeper and wider than the plant's root ball loosens the soil for easier root penetration as the plant grows. Place the dirt on a tarp.
Refill the base of the hole up to where the root ball will rest using a blend of about one-quarter compost or leaf mold to three-quarters soil. Also add a slow-release fertilizer according to the manufacturer's instructions. You can blend the soil on the tarp or in a bucket or wheel barrow.
Drop the root ball into the hole with the crown (top of the root ball) at ground level. Backfill the hole pressing down the soil as you go to force out air pockets. If you are trying to make the soil more acidic to create deeper blue blooms, then apply aluminum sulfate around the hydrangea according to manufacturer's instructions. Encourage pink blooms by adding lime (a chemical compound produced from limestone) around the plant according to manufacturer's instructions. Applications of aluminum sulfate or lime might need to be repeated in the spring and fall until the desired bloom color is reached.