Hey Judy, While the spike is not important for photosynthesis, you can cut it right above the highest leaf anytime after flowering or just let it turn brown and dry up, then cut it off. Either way would work

i would be alarmed if this happend to mine! lol, glad you posted this tom. in regards to the watering seedlings question,im working on the theory that they must have to put up with the same amount of rain fall in the wild as there parents so ive let my seedlings grow solid for just over a full year now to get them to a size were they look like they can handle themselves.ill probably stop watering in june let them go dorment and bake in the sun. ill let you all know how many survive lol ben

Could have been the watering issue. Could also be herbicide drift or the sun baking the roots in the black pots. tj

Hydrangea flowerheads can become discolored if the blooms are finished, they have been somehow damaged/bruised during transport or planting, if they have been scorched by sun or if they have had too much water directed on them. It is not a disease or insect problem but just something that occurs due to one or more of these factors. You can just remove them if you find the appearance unsightly but I wouldn't do any other pruning except just the deadheading, if you so desire.