A quick look around the late-summer garden confirms why a popular hydrangea variety is named “Endless Summer.” Where other former glories of the perennial border are faded, browned and bug-bitten, hydrangeas in all colors are foaming with blossoms, as fresh as they were two months ago. Our plants have been in place for five years or so, and this is the best display we can remember since they first began blooming.

The Endless Summer hydrangeas, introduced about a decade ago, were a real breakthrough for northern gardens with harsh winters. Older hydrangea varieties bloomed only on old wood or stems from the previous season’s growth. If that growth was lost to severe winter conditions, or to inadvertent fall pruning, all flowers for the following season were lost. But Endless Summers bloom on both new and old wood, making the plants much more versatile. The only caveat is that if plants are not properly fertilized in the spring, few buds will be produced on the current season’s growth.  Other than that, these hydrangeas are happiest if they are planted where they’ll get  full sun, at least for five or six hours a day. Don’t go by the nursery tag that comes with the plant, which says it can thrive in some shade; in Zone Four, the plants prefer more warmth, as well as compost-rich soil that will retain moisture and thus hold nutrients and fertilizers well. If you want those big blue blooms, fertilize in the spring with Holly-tone for blue flowers or Plant-tone and granulated lime for purple to pink flowers. For best flowering, fertilize in April, May and June; plants should not be fertilized after that, because you don’t want to encourage new growth before winter. 

In this area, pruning should be done in late spring, when flower buds that have made it through the winter have emerged. Prune out only dead wood and leave any green buds or leaves. While taking out the dead wood you may find, as we usually do, leaves that have been curled up  into a pouch, the work of the hydrangea leaftier, which lays its eggs on a leaf, then spins a gossamer silk blanket to wrap around the eggs, attaching them to the leaf as they do so. The silky material curls the leaf, thus hiding the eggs from birds and other prey, and the grub feeds on the flower bud within. As the leaf continues to grow, it takes on the shape of the aforementioned pouch. The larva eats its way through the bud and leaf, eventually emerging in June or July as an adult moth, ready to begin the cycle anew. If you clip all these egg cases away and dispose of them by burning or shredding the cases, the cycle of reinfestation is broken. Of course this means you may lose a flower bud, but there can be time for the plant to form new buds and, in a banner year like this one, there are ample flowers. 

Deadheading mophead hydrangeas, whether a younger or older plant, is a good practice throughout most of the summer because it encourages new blooms. Cut the stem just above the first set of leaves beneath the spent flower at approximately a 30-degree angle. Using this technique throughout the growing season will maximize the number of blooms on your Endless Summer hydrangea. However, stop any cutting of blossoms around this time, or risk losing next year’s flower buds, which are being produced right now. Instead, leave spent blooms on the plant to give some winter interest to the landscape. This also has the added benefit of insulating new buds for next season.  Once spring arrives, you can cut away these blooms when you do your cleanup pruning.