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How to Care For Endless Summer Hydrangea

Here at Gertens, we offer professional advice on how to care for Endless Summer Hydrangea. Read on to learn about this relatively new species and the growing conditions it likes best.

Endless Summer Hydrangea is a Hydrangea macrophylla that was discovered by Vern Black of Bailey Nurseries in 1983. Vern was impressed with the amount of bloom and hardiness of plant in a Zone 4 climate where H. macrophylla generally performs poorly as the buds set the previous year are typically killed in most winters.

In 1988, plants of Endless Summer were observed by Dr. Mike Dirr, who took cuttings back to the University of Georgia's Center for Applied Nursery Research for further testing. Dr. Dirr is quite impressed with Endless Summer, particularly because of its ability to consistently bloom on new wood. It was his encouragement that led Bailey Nurseries to take this plant quite seriously in terms of introduction. He currently has a number of studies in progress with Endless Summer that will help us further define its attributes and production.

Characteristics based on current results/experience:

  • Endless Summer is a mop-head type with clear pink blooms in soils with poor aluminum uptake typically alkaline soils, and blue flowers in acidic soils with sufficient aluminum. Blue flowers can be achieved in alkaline soils by adding aluminum sulphate to the soil to change the soil PH. Flower size is 4 to 6 inches across under garden conditions, and up to 8" in diameter on vigorous container plants.
  • The most unique characteristic of Endless Summer is its ability to bloom on new wood. If the new emerging growth is cut back to half, the amount of bloom is significantly increased. In addition, removal of spent blooms results in repeat bloom. If spent blooms are removed, one can have bloom from June until frost in Minnesota, and from June until November or frost in Georgia.
  • Endless Summer has performed well in Zone 4, although it is not as stem hardy as Nikko Blue. Its ability to bloom on new growth has resulted in dependable bloom, thereby extending the range for successful bloom with H. macrophylla.
  • Endless Summer has good foliage, medium to deep green with good substance, and is mildew resistant. In comparison to some cultivars, resistance is definitely better than Nikko Blue.
  • Endless Summer appears to have potential as a potted plant as it has the ability to set flower buds on new growth without a cold treatment. Studies are currently underway by Dr. Neil Anderson at the University of Minnesota to more clearly define potted plant production.
  • Mature plant size is 3 to 5 feet in width and height.

How to care for your Endless Summer Hydrangea

  • The Endless Summer Hydrangea is slow to break dormancy, and will not start to grow until the ground has sufficiently warmed up. This could be as late as early to mid-June. Be patient, you may only get growth from the base of the plant coming up from the soil.
  • Once you see growth, you can cut the dead branches back to the new green growth. This is the time to apply fertilizer and Aluminum Sulphate for blue flowers.
  • You should see some signs of blooms by the middle of July.
  • Stop fertilizing in mid-August so the shrubs can begin going dormant.
  • Keep the soil moist until the ground freezes.
  • Cut the shrubs back to around 8-12". You will need to cover the plant in order to winterize it. This can be accomplished with leaves, straw or other similar material.
  • Do not cover the plant until it is full dormant. This is usually around the end of November, around the same time that you would normally cover perennials in your garden. An easy trick is to fill a plastic garbage bag with leaves from your yard, and then gently set it on top of the plant. When the ground thaws in the spring, simply remove the bag and there is no mess to clean up. Regardless of how much you mulch, plan on taking the mulch off the plant when you uncover your perennials after the ground thaws.