Answer: Endless Summer is special in that it is able to bloom on both old and new wood. This means it blooms over an extended season, first on stems that grew the year before, and later on in the summer and fall on growth of the current season. For best blooming, it must overwinter without damage to the stems and then it must grow vigorously throughout the season.
It will do best in a location with protection from winter winds, with soil that is evenly moist yet well drained, and with good fertility. It needs direct sun all morning or bright dappled light all day. Using an organic mulch year round helps to maintain steady soil moisture as well as feeds the soil slowly as it breaks down over time.
The flower color is related to the pH of the soil. Pink blooms indicate a neutral or slightly alkaline pH. For blue blooms, you need to acidify the soil slightly. To do this you can use an acidic mulch such as pine needles or pine bark along with a fertilizer for acid loving plants such as Hollytone. (Read and follow the directions.)
Also, do not use any lime near the plant as this reduces acidity. If the soil was limed prior to planting your hydrangea, it will take time for that lime to leach out of the soil. Planting the hydrangea near concrete, especially new concrete, can also cause change to the soil pH due to its leaching lime into the soil.
If the acidic mulch and fertilizer do not work over a year or so, you can also use sulfur to treat the soil. (Aluminum sulfate is sometimes recommended but in excessive amounts it is toxic to plants so I do not suggest it.) It is best to do any adjustments to pH gradually and to test the pH periodically to check the progress. Your local county extension should be able to help you with the testing and interpreting the results. You can test for fertility at the same time as you test for pH.
Common reasons for poor blooming include winter damage, excessive pruning, lack of sunlight, lack of fertility, and lack of moisture. To help you trouble shoot, here is the web site devoted to this plant. It includes care recommendations.
Keep in mind also that it needs a year or two to settle into its new location becoming rooted and fully established before it will bloom its best. Good luck with your hydrangea!
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