The spent flowers could be deadheaded but it such a large specimen now that (a) it may take "forever" or (b) you may not be able to reach many of the top blooms. I would try to remove dead wood regularly but I would do this around the month of May when it is clear which parts are dry and which ones are just dormant. Opening some areas in the top so light can reach the bottom leaves is always useful too (or thin out the leaves a little).

Besides this, you can just do the usual things. Apply 3-4" of mulch up to or beyond the drip line so the roots do not have to be watered often. Add a layer of fertilizer below the mulch using either cottonseed meal, compost or well composted manure. Maintain the soil evenly moist as best as you can. And in case this applies to your soil, amend the soil to acidify if you notice signs of iron chlorosis.

This post was edited by luis_pr on Mon, Apr 1, 13 at 7:17

We removed a ton of brittle dead woodcfrom underneath this weekend but will follow up in May with any we missed.

Thank you for your help! Any clue what type of hydrangea this is?

Probably a Hydrangea paniculata Pee Gee. Very common in the NE. I have seen a lot of tree form Pee Gees in MA and NH during my travels there.

Just a guess though. Many paniculatas are grown in tree form now a days but before that, it was mostly the Pee Gee. See the link below.

Here is a link that might be useful: Pee Gee Hydrangea & other paniculata varieties

This post was edited by luis_pr on Mon, Apr 1, 13 at 20:22