In cooler northern climates, here are some steps we can take to help ensure better bloom production for our hydrangeas.
In northern climates, the location of your hydrangea in the garden will have a large impact on bloom production. The farther north you are, the more sun your plants need and can tolerate. In zones 4-5a, plant your hydrangeas in a location that enables them to receive at least 6 hours of sun with some dappled shade in the afternoon.
Stop cutting plants to the ground. Most, if not all, of the flower buds on old wood are being removed. If the plants bloom only on old wood, you are certainly trimming off the flower buds for the next year. We recommend spring trimming to remove dead branches or to shape your plant. Endless Summer Hydrangeas and many of the other newer re-blooming types do bloom on new wood, but it may take longer for flower buds to develop on the new growth of a young plant. Once the plant begins to bloom, deadhead and trim to maintain the shape.Winter Cover Protection for the plants in the first few years is important, as is protection from spring freezes. Since Hydrangea buds emerge early in spring, late freezes may damage bud development as well as any new growth. Keeping the crown of the plants covered with mulch helps protect these buds and any soft new growth from late spring freezes. Be sure to use loose-composted mulch. You also need to watch that the material does not stay wet, in order to avoid rotting the plant. You can use burlap and/or cones manufactured for early spring protection.
The first thing all gardeners should do is a soil test to give you a good starting point. Fertilization is an important factor in flower production of Hydrangeas. A good quality, slow release fertilizer applied once in spring or early summer should be sufficient. If you over fertilize your hydrangeas, the effect is usually dark green leaf production with fewer flower buds. In the northern zones, it is recommended that you stop fertilizing after August 15th, as plants need to slow down and acclimate for winter.
Changing Flower Color
The first step is to learn the pH of your soil. Purchasing a test kit from your local garden center will help in determining your soil pH. To change flowers from blue to pink, you need to change from an acid soil to an alkaline one (pH of about 6.0 to 6.2). Many soils in our area are naturally alkaline, and will produce pink blooms with no extra effort. Changing blooms form pink to blue is achieved by lowering the pH of your soil to a level of about 5.2-5.5. This is achieved by using a soil acidifier.