99% of hydrangea macrophylla / serrata bloom on primarily old wood.

All oakleafs (quercifolia) bloom on old wood, but are more winter-hardy. Most people's oakleafs that don't have deer eat the buds in the winter time.

New wood varieties include hydrangea arborescens and paniculata, but both are primarily white with a few pinks.

Any other simple answers you may be seeking are littered throughout this forum (going back many years) and the net (there are sites completely devoted to hydrangeas).

After this last Winter caused the same setback you're seeing - hydrangeas that bloom on old wood that suffered dieback won't bloom this year - many of us are looking at the "reblooming" macrophylla (mophead) & serrata (lacecap) with renewed interest. As Springwood says, most of the mopheads & serratas bloom on "old" wood - stems that are at least a year old.These set buds mid-Summer to Fall (depending on your zone & local weather) that bloom the following year. Buds can be killed by cold, as can entire branches.

Those that bloom on "new" wood - branches that grow in the current season - bypass the setback old wood bloomers can encounter. "Reblooming" varieties can bloom on last year's old wood AND this year's new branches. If the old wood buds are killed, new wood will still bloom if your growing season is long enough.

Some are calling those that bloom only on new wood "rebloomers" if new branches grow additional stems that bloom later. The fine line between "rebloom" and "extended bloom" can become confusing. If you want mopheads & lacecaps that can bloom early in the Summer on old wood & later in the season on new wood - so you will have at least one set of blooms every year - look for varieties with info about blooming on old & new wood.

Many new varieties have been & are being introduced to market in recent years. A good bit of discussion here reviews introducers' claims and personal experiences growing them in our gardens.

The wonderful advantage to having the 'Endless Summer' types of hydrangeas (there are now many on the market); is that when it comes to pruning them -- these plants bloom on new and old wood. You do not have to worry about lost buds due to improper timing of pruning or bud loss due to extremely cold winters (which is what the OP is discussing).

Unless you are looking for blue blooms, h. arborescens and h.paniculata hydrangeas are the way to go. Annabelle is an excellent h. aborenscens--white; some popular h. paniculatas are the two-toned pink and white Vanilla Strawberry and Pinky Winky (and others) or the white Limelight (larger) or Little Lime (smaller---but not that small--just 5 ft compared to the 10 ft of Limelight). There are a number of other h. paniculatas also. They bloom during the last half of summer. The h. aborenscens bloom the first half of the summer.

If you live in Zone 6 (or at least in my zone 6), you can count on most of your h. macrophyllas NOT BLOOMING at least 50% of the time. Winters are too cold.

Kate