If the old wood regularly dies off, ensure you are removing the winter protection by or after your city’s average date of last frost, not before then; ensure your last fertilizer application is done 3 months before your average date of first frost; ensure you maintain 3-4” of mulch past the drip line and water if dry at a depth of 4” while still above freezing (reduce the amt of water once leaves brown out but avoid letting the soil get bone dry while above freezing). If the problem persists, discontinue winter protection. Also, consider instead remontant cultivars whose maximum height is either 3 feet or less as these will bloom earlier in late summer/fall compared to tall remontant varieties like ES Original; so, consider Summer Crush, Pop Star, varieties of the Let’s Dance Collection, etc. Note: a December 22nd Arctic Blast probably killed last year’s spring flush.

As the first of the remontant or new wood flowering hydrangeas on the commercial market, Endless Summer The Original has a dismal track record of reliable new growth blooming in colder zones. It has not earned the nickname of Endless Bummer by accident!!

While even with winter protection, you are unlikely to ever get the old wood to survive winter cold and flower, new wood growth and flowering can be extremely variable and iffy as well.

For more reliable flowering of a bigleaf hydrangea in your climate, I'd suggest considering one or more of the varieties luis mentions. Even the later Endless Summer introductions are more likely to produce reliable new growth flowering than The Original.

I'd still recommend winter protection however.

Thank you everyone for all the great information! I did not know I should not fertilizer later in summer. Good information!

@luis_pr Can you elaborate on proper fertilizing times for my Endless Summers?

My Endless summer at three years in the ground took to budding flowers in September and it was a race for a bloom before frost. After 10 years I took them out since they had become Endless Bummers. Mid MN does not seem to have the growing season for these plants.

The remontant hydrangeas that were originally introduced eons ago under the Endless Summer (ES) Collection (and others) would develop spring blooms as any non-remontant hydrangea does in spring (via dormant, spring flower buds created the previous year) and then they would produce a second flush once the new spring stem growth got tall enough to trigger flower buds and immediate blooming. The problem is the second flush in some areas would not get sufficiently tall until September or so. Newer remontant hybrids, like ES Summer Crush, ES Pop Star or the Let’s Dance Collection (which includes varieties that get as tall as from around 3 feet tall to 1-2 feet tall) are more compact and will trigger the second flush of blooms much earlier. Give those that get no taller than about 3 feet tall or less a try.

@Molly D. Zone4B I just saw your question. Sorry. You can start fertilizing if in the ground after your city’s average date of last frost; only water and mulch before then. If you fertilize before then, new foliage and new stems triggered by the early fertilization may get killed by late frosts (but that does not typically kill the plant though). Stop fertilizing about three months before your city’s average date of first frost. See your fertilizer label for fertilizer amounts and when to re-apply the fertilizer (usually every 3 months or so) but, if using Holly-tone, apply it at full strength by your city’s average date of last frost and only one more time again at half strength 3 months before your city’s average date of first frost.

Thank you Luis! Great information! I usually just use a generic fertilizer but never really had a plan.

It’s minus 10 right now so just dreaming about gardening….

You can use a general purpose fertilizer with a NPK Ratio of around 10-10-10, organic compost, composted manure, cottonseed meal, Holly-tone, etc. It is 9F Low here in the Dallas area and we just got dusted with a tad (< 1”) of snow. Highs in the 20s. Too cold to garden though. But in the 50s Wednesday. Hope your high gets above 0F as something silly like that makes me feel warmer.