When planting hydrangeas, protect the root ball – keep it moist. Don’t break it apart when planting. Hydrangeas have shallow, fibrous roots.
Plant hydrangeas in part shade, or in morning sun with afternoon shade.
Dig a hole twice as deep and wide as the root mass. Mix in a small amount of bone meal or starter fertilizer. Set the plant no deeper than it was in the pot. Do not bury the crown.
Hydrangeas do not like to be dry. Water them at the base, to keep from breaking off the foliage and flowers. They are very resilient. If they are wilted, water them well and they will recover.
Expect a hydrangea to take a year or more to naturalize to its new soil chemistry before it comes true to its color heritage. If you want to try to adjust its color, acid soil produces BLUE (Aluminum sulfate, 3-4 Tbs. per gallon in water as a drench. Apply it twice, 14 days apart) and neutral soil produces PINK (Dolomite lime, 3-8 cups sprinkled around the base of a large shrub.) Apply these minerals in the fall 4-6 months before bloom time. White flowered shrubs cannot be changed.
Hydrangeas don’t need a lot of pruning. You can prune a hydrangea to remove very old wood that is clogging up the middle. You can take out 3-5 canes per year, cutting them off at ground level.
Other grooming should be done in late winter just as the new leaf buds (oval shaped green bumps on the stems) start to show in February and March. Don’t prune any later or you’ll be removing potential flowers. Cut the stem ½ inch above the second highest set of leaf buds from the top. (When you cut the stem above a set of 2 leaf buds, those leaf buds will make 2 new stems and each will flower, so you will have twice the flowers.)
Hydrangeas do not generally need much fertilizer. If you want to give them a boost, feed them a balanced high acid fertilizer, such as you would use on rhododendrons or camellias. Too much nitrogen will give you all foliage and few flowers. Apply fertilizer in February and March at the same time you are grooming the plants.