Pink Elf is just a trade name for Hydrangea macrophylla 'Pia'. You can search under either of those names for more info. This is a dwarf form, rarely exceeding 3'x3', and is an excellent choice for containers. In zone 9, holding in a container overwinter will be fine. Make sure they have afternoon shade and even moisture. 'Pia' is one of the few pink flowered mopheads that retains its very pink coloring regardless of soil conditions.

Sorry, must disagree with the marketing hyperbole about 'Pia' ('Pink Elf').
In my very acidic soil, they produce deep purple blooms each year. Attractive, to me, but certainly not pink, as advertised. They are of a short stature, maturing to about 3½-4 ft. tall.
Grown in a good potting mix, they will most likely produce pink flowers.

Well. I potted one today! Need to get another pot tomorrow.
I'm wondering if the 2 hydrangeas that I planted some years ago, failed after a few years because of competition from oak tree and pine roots. The lighting seemed right and the first few years they were beautiful.