How to Keep Outdoor Potted Hydrangeas Flowering All Summer

Pot the hydrangea in a mixture of two-thirds sphagnum peat moss, one-third quality potting soil or builder’s sand and ½ teaspoon of 14-14-14 fertilizer. If your hydrangea is growing in an 8-inch pot, double the amount of fertilizer. Terra cotta pots are ideal because they’re porous and won’t hold excess moisture near the hydrangea’s roots.

Place the potted hydrangea in an area that receives morning sun and afternoon shade. Too dense or too much shade discourages blooming.

Irrigate the hydrangea at the soil and not overhead. Wet foliage and flowers encourage fungal disease, which affects the flowers' beauty. Water the plant often enough to keep the soil evenly moist. Supply the water slowly to ensure that the entire root ball is moistened. Pay close attention to the moisture content of the soil during warm, dry weather since it will dry out faster than you're accustomed to.

Water the potted hydrangea with a fertilizer solution – 1 teaspoon of 20-20-20 in a gallon of water – once a week.

Prune the oakleaf hydrangea (H. quercifolia) and the mopheads and lacecaps (H. macrophylla) in the summer, before August. The ideal time to prune them is right after they finish blooming. If you prune in August or later you will be pruning off buds that will bloom the next season. Prune Hydrangea paniculata and Hydrangea arborescens in fall or winter. Remove dead wood, branches that cross over each other and to shape the plant to your specifications. Never remove more than a third of the plant's branches.