The number of blooms will be larger on an older plant since they tend to have more stems but hydrangeas tend to grow somewhat fast and a 1 g plant would "soon" become a 3g plant, all things being equal.

If you deadhead, you will get new blooms only from Hydrangea macrophyllas that are rebloomers. Rebloomers produce blooms at the usual time (around July-August -say- of 2013 and again during the 2014 growing season) but non-rebloomers only produce flower buds in July-August every year.

Paniculatas are not rebloomers so the blooms stay "on" until you deadhead them or until they blooms slowly disintegrate. As the blooms fade, they will change colors until they end brown. Paniculatas usually produce flower buds after they leaf out in Spring. The date when paniculatas start to blooms varies; from late June thru late July or August (it depends on which paniculata you get and where do you live).

The blooms of all hydrangeas "work" like that so you could say that, generally speaking, the blooms always last a long time (although I would say that some of my Hydrangea macrophylla lacecaps have blooms that last less)

Luis

OK, I fully grasp the paniculate situation now. You mentioned reblooming varieties (macs) and now I'm a little confused on that front =(

Macs will bloom in the usual time, July to august, then if you deadhead them they will not bloom again until the next season?

I apologize in advance if these are dumb questions... I feel silly writing them out =/

Thank you in advance for your patience

The macs will produce invisible flower buds in July-August; these flower buds become blooms in early Spring. After that first flush, the rebloomer macs produce flower buds again and you get bloomage a 2nd time. The non-rebloomer macs just bloom once and the flowers stay "on" until you deadhead them or they fall.

Rebloomers macs will trigger additional flushes of buds/blooms faster if you deadhead the blooms as soon as the colors fade.

My reblooming Macs start blooming in late June/early July since they get killed back to the snow line most winters. In milder climates I imagine they start earlier. They keep pushing out new blooms all summer.

I cut off the previous year's dead blooms of my H. paniculatas in spring before they start leafing out. (I find the dried blossoms ornamental against the winter snow.) They will start this year's blooms in late June or early July. Here are some photos from last year, all the same set of flowers (no pruning) on H. paniculata 'Quick Fire'.
June 30 with the white flowers just starting to open (the purple flowers are from a clematis that climbs into it.)

I think that H. paniculata is the longest blooming plant I have, in particular 'Quick Fire.'

Thank you! And back to the 1 gallon vs 3 gallon, will the 1 gallon put out 50% of the flowers of the 3 gallon the first year? What I'm aiming for is if its worth it if I'm concerned about getting the most blooms the first year, quantity particularly. Size is of seconardy importance if its an inch or two difference

Only God knows. There are too many what-if possibilities out there.

If you assume that all the stems are alive, and also assume that all stems will develop one invisible flower bud at the end of the tip and if you also assume that all flower buds will produce blooms then you could argue that the plant with the most stems would have the most blooms and select the shrub with the most stems.

The problem is that some stems may not bloom for reasons x-y-z so until the flowers bloom, you do not know for sure which one container size will have more blooms. You can only pick the one with the most stems.

But beware. It is possible that you could even buy the shrub with the most stems and, once the plant blooms, you could discover that the paniculata in the container is not the one that plant label describes! I bought a mophead once that turned out to be a lacecap because of mislabeling by someone.

If the number of blooms is so critical, you could wait until they bloom and then buy accordingly.

A few clarifications here.

1. A larger pot size doesn't necessarily indicate a "large enough" plant. And this is known as a rip-off. Some nurseries (and Lowe's right now) try to sell 3-gallon pots with one-foot tall plants with three to four branches for $25+. Not a value. It's best to keep looking at as many nurseries and stores as you can visit until you can find a suitably sized plant. A decent 3-gallon potted panicle hydrangea should be at least 2-3' in height, not including pot, and have at least 10-20 significant branches on it, and it shouldn't cost more than about $35. I found a mis-priced 3-gallon Little Lime a couple years back for $15, and it was already 2' tall and had more than 30 branches on it.

2. Quick Fire is among the earliest to bloom (June). There are some others close to it (like Snow Mountain), but you'd need to do further research. The older Grandiflora blooms a bit later (~August), in contrast.

3. Paniculatas can technically rebloom, but the season isn't long enough to allow this. What you CAN do is delay blooming, if you like. Say you want Limelight to bloom in September instead of July. You'd cut the partially or fully-formed flower buds off just before blooming, and it'll take about 1-2 months to regenerate buds. Some people do this who have multiples of the same plant and want the blooms to differ in appearance depending on time of season. And other times it's a mistake, as I once witnessed a landscape crew knock 2' off a Limelight hedge, which delayed blooming unti September.

(Quick Fire's budding is finicky, so don't attempt to delay blooming on that plant. Not all paniculatas were created equal.)

This post was edited by Springwood_Gardens on Thu, May 15, 14 at 13:27

Let's add this for "reblooming" macrophyllas......the only thing reblooming about them is their ability to flower on both old and new growth. In zone 5 if not protected over winter, flower buds on the old growth (if not the older stems themselves) will be killed off by cold. One can certainly expect flowering on the new growth produced that season but not until later in the season and definitely not in a "reblooming" mode, deadheaded or not.

I would also say that in most cases, bigleaf hydrangeas are NOT recommended for full sun. Even in my very northerly and mild summer heat zone, full sun is an extreme setting for macs and they will wilt daily. Best for full sun are any of the paniculatas, which are also some of the most drought tolerant varieties as well.