Can you recommend a blue hydrangea that repeat blooms? How do you stop them from getting too large? Prune?

The best way to keep them small or med. size is to buy ones that mature to the size that you want. There are specifications found on hydrangea websites and in the descriptions of each plant found on nursery websites. The problem is that the color and final size is variable. Hydrangeas can look blue in a photograph but be pink in your garden. In many varieties the color depends on the soil as well as where it is grown, sun or shade. Pruning a hydrangea to 2-3 feet that is expected to grow 6-8 feet will result in a plant that does not usually make a beautiful small hydrangea. Most commercial potting soil that I have used for hydrangeas results in pink flowers, when the same plant is planted in the acidic soil in the garden they turn blue or purple or magenta. But not all! There are ways to change the ph of your soil, but personally, I find the mystery of the color of new plants part of the charm of Hydrangeas.

One of my favorite smallish - 3 x 3 ft is Hydrangea Macrophylla Henrik Seidel. It is blue in my garden and I bought mine from Joy Creek Nursery. HydrangeasPlus is another nursery on the east coast that carries it. Check it out in the Joy Creek online catalog. Here is a photo of Henrik from my garden - small plant but huge flower heads.

Proven Winner's Let's Dance Series includes many compact, reblooming H. macrophyllas. Do an Internet search for "hydrangea let's dance". I think you can directly buy from that wholesaler via their website if you want. But of course, it is winter; if something shows up as 'sold oout' in their website, you may have to wait until their stock is replenished. The wholesaler for Forever and Ever mophead/lacecap hydrangeas does not sell directly to the public but I usually see their F&E hydrangeas for sale at Walmart or Lowes.

Mopheads (H. macrophyllas) that bloom white cannot change the bloom color by amending the soil but pink, purple or blue mopheads can. Acidic soil makes the blooms turn blue. Alakline soils make the bloom turn pink. A nearby plant nursery can give you an idea of how alkaline or acidic soils are in your area; you can also get a soil pH kit there too so you can check yourself.

Are hydrangeas relatively hard to grow compared to roses?

Well, they are like apples and oranges. Hydrangeas require more water
than roses and they also do best in morning sun / afternoon shade (so
their leaves will not develop sun-scorch). In the northern areas of the
country, some can be planted in full sun but down here, they would croak
if put in full sun. Roses require at least 6 hours of sun or they get
spindly and suffer a lot from fungal diseases (think black spot).
As long as you supply hydrangeas with appropriate amounts of water
and as long as you provide adequate levels of sun & shade, they are
fine and tolerate other issues very well. If planted where they can
attain their estimated size at maturity, they will not require but minor
pruning (to remove dead wood in Spring) while I always have to prune
the roses around Valentine's Day or so (I have almost 80 roses so it takes me a while to prune and end up bleeding due to thorns). On the other hand, roses tolerate alkalinity better than hydrangeas and I very rarely notice signs of iron chlorosis in roses.

Much easier in our growing zone in the Pacific Northwest. Zone 7-8. Our temperatures are moderate, lots of rain and few really hot spells in the summer. In fact, hydrangeas have been growing in our Marine climate for thousands of years and hydrangea fossils can be found at many digs along with other ancient plants and creatures. Hydrangeas are a huge group of plants and the trick to growing them successfully is to choose plants that will thrive in your particular climate. Visits nurseries, check in your neighborhood or garden club. Ask Master Gardeners and read all about them. On-line catalogs are a wonderful and thrifty way to get started and of course Garden Web and other on line forums are helpful.

Personally, I find them far more beautiful and easy to grow than roses and I grew many different kinds in my Northern California garden. The bloom time is much longer and all the pruning and fussing that roses require is not needed. In our garden, there are no issues with bugs or other maladies. The colors are endless and the variations in the shrub and blossom sizes and shapes are beautiful and interesting.

Luis - looks like we replied at the same time! lol But, no controversy!