Good evening Rj,

Endless Summer (also called Big Leaf) hydrangeas are known botanically as Hydrangea macrophylla. They typically set flower buds on old wood from the previous year (although it also blooms on new wood), like azaleas. If you prune these plants early, you remove those flower buds. That means you prune bigleaf and oakleaf hydrangea later in the spring after they flower.

Some additional possibilities:

1. The flower bud can become damaged, killed by drastic temperature changes in winter. The plant, mainly the root system, is winter hardy, but the flower buds and branches are not as tolerant of rapidly changing fluctuations in temperatures. Genetically these plants are still programmed to bloom best on the old wood. Summer blooms develop best when summer days and nights are cooler. Let me also mention this species is a water hog and needs ample moisture.

1. Not be enough fertilizer. To bloom well, this plant needs to be well fed. It benefits from a constant fertilization schedule. Be careful not to overfeed and burn the plant due to fertilizer toxicity.

1. Too much Nitrogen fertilizer. Too much Nitrogen (the first of 3 numbers on the fertilizer label) will encourage lush leafy growth and few or no flowers. Consider whether the plant receives runoff water from your lawn (most lawn fertilizers are high in Nitrogen) and receives excess Nitrogen from that source. If you have not had your soil tested, I’d recommend having that done. You can order your kit here: https://homesoiltest.msu.edu/get-started

1. Poor watering: The soil should never dry out, nor should the soil ever be sopping wet. Stressed plants will produce fewer flowers.

https://www.johnson.k-state.edu/lawn-garden/agent-articles/trees-shrubs/hydrangea-macrophylla.html

https://ask2.extension.org/kb/faq.php?id=204914

Endless Summer with proper care will bloom later this season, since it does bloom on old and new wood. Branch County had a freeze event on 04/06/24 and the flower buds were probably killed at that time, if they weren’t pruned off or killed over winter.

Rebecca Finneran earlier recommended the “Let’s Dance” series as being more dependable than Endless Summer here in Michigan.

Good luck & have a great day!