Hi, 

If you can, plant now, don't wait until fall unless there's a reason it has to spend the summer in a container. Any plant will be less likely to succumb to winter damage if its roots are in the ground for the winter, not a pot

Unless you would like to change the flower color, don't worry about trying to acidify the potting mix to a certain degree just for the summer, or even if you decide to plant in the ground. It usually takes some time to change the pH level to effect bloom color too, so if that is a goal, just be aware if you don't see immediate results. 

If you are trying to transplant the young propagated plants by the fall, be prepared to protect them from any rabbits or deer from browsing, as young hydrangea stems seem to be a favorite. 

Emily

Another stupid question.I don’t really see any buds on these for new flowers. How do you know they’re going to flower?

Thanks for such good information now I have a couple more questions.

Hydrangea flowering depends on the type of hydrangea being grown. Some species bloom on "old wood" while others bloom on "new wood" (a few do both).

Old wood refers to the stem growth produced the prior year.  Hydrangeas that bloom on old wood develop their flower buds the summer or autumn before they open, meaning that the blooms you'd see this May/June/July actually formed last growing season and remained fully-formed but small and dormant all winter. They open this summer and no new ones are produced to follow them after they fade, only the buds that grow later in summer to repeat the process as dormant buds that wait for next summer. New wood is the growth produced the current year, and for some species this younger growth is able to flower without needing to mature more. Since the plants blooming on new wood don't have flower buds lying dormant on the stems all winter, they are less likely to lose them to extreme cold, pruning at the wrong time, deer browsing, and other issues that kill or remove those buds which the plant cannot replace in time for that year's bloom.

Smooth Hydrangea (botanical name Hydrangea arborescens) and Panicle Hydrangea (Hydrangea paniculata) both bloom on new wood only. Oakleaf Hydrangea (Hydrangea quercifolia) blooms on old wood only. The remaining group, the Bigleaf (Hydrangea macrophylla) and their close cousins Mountain Hydrangeas (Hydrangea serrata) can be mixed. Most varieties in this group bloom on old wood only. Some varieties (a growing number every few years as plant breeders make more) can do both -- old wood flowers open first and then are followed by new wood blooms, allowing the plants to bloom essentially all summer in succession. The same process repeats itself, where by late summer the plants are growing buds for next year's blooms that will sit dormant on the stems all winter.

This means that it's hard to tell what caused poor blooming in the early part of the season for macrophylla and serrata varieties, especially if you don't happen to know the name of the variety being grown. ("Reblooming" or "remotant" is the descriptive term used for the varieties that can bloom on both old and new wood.) If the plants had their branch tips trimmed or bitten-off by deer anytime between about August and throughout winter, old wood flower buds could have been lost. Plants that were fine until a spring freeze after a mild spell caused the shrubs to break dormancy and begin swelling buds for growth can also lose flowers because they are then more vulnerable to a cold snap. Some Bigleaf Hydrangea varieties are also less cold-hardy (particularly those sold in-bloom in early or mid-spring, like around Easter) because they are forced for decorative use rather than in-garden hardy shrub use. Overall, flower buds are less cold-hardy than leaf buds while dormant, and some of those "florist" potted tabletop hydrangea varieties will survive outdoors here in gardens but not flower reliably well because of this hardiness difference.

You might not see flower buds this early yet, depending on what kind of hydrangea this is. (We might be able to determine the species from photos, but we can't ID it to specific variety from its appearance alone.) If for some reason flowers don't appear this year but the plant remains healthy, there's still hope it can flower in a following year.

If you happen to be growing a reblooming hydrangea variety, then cutting stems for propagation or cut-flower use won't detract much from its ability to continue blooming, though it can take the cut stems some time to regrow enough to open new flowers so there will be a delay on that particular part of the plant.

Miri

So am I correct that you are saying that over time the plant will eventually bloom because of the new growth it produces?The variety I have is HI River Blue

Although we can't find much detail about that exact cultivar online, it appears to be part of a series that are bred as "florist" hydrangeas. These are given that category name because they're grown as potted plants for more impulse and decorative uses (like cut flowers, but in this case as a live blooming plant). Florist hydrangeas tend to be stocked/sold and promoted in spring (and usually around the Easter holiday when shoppers are looking for colorful in-home décor) by nurseries before their typical outdoor-hardy hydrangea stock has arrived (and certainly before they have begun to bloom, even if they have already received those shipments alongside other hardy shrubs).

Given that, you will want to find a sheltered location to try growing the "mother" plant as well as its cuttings, since florist-type hydrangeas are not bred for great winter cold tolerance since that's not the focus of their breeding and use. The plant will probably overwinter just fine in terms of foliage, though a harsh winter or sharp drop in temperatures after a mild spell in late winter could still damage branches. Instead, though, the more vulnerable part of the plant will be its dormant flower buds, and we suspect it's also not a reblooming variety since the breeding of florist types also do not prioritize this since they're displayed for a relatively short period of time. Growing the plants near a south-facing wall of the home, for example, or perhaps near a solid fence to block the winter winds, may help give it a few degrees of winter cold protection in order to let those dormant flower buds not succumb to the weather. Don't plant it so close that it has little room to grow or receive good air circulation to keep the foliage from contracting leaf spot diseases, but the structure nearby can absorb and radiate a few degrees of heat in the colder months and might be all it needs along with a layer of mulch over the roots. (Keep mulch off the stems themselves and the layer should be only about 2 to 3 inches thick to avoid smothering the roots.)

We can't predict how well it will bloom between this presumed bud hardiness issue plus the timing of the trimming for cuttings, but once that trimming has stopped because you're finished taking cuttings, it might bloom normally on old wood each May/June (or thereabouts).

Miri