I have two Cardinal Reds (1 gal.) that I'm going to put in a part sun raised bed (not extremely big, hydrangeas will be the focal point, once mature). I'm thinking that I'd like to keep them red (so I should keep the pH neutral? slightly acid?), but would like to reserve the option to turn them blue later... any suggestions on what to plant with them in the same bed, other than azaleas/camelias/other large woody shrubs... smaller perennials/bulbs/annuals that would do well in the same environment & compliment my hyrdrangeas? Thanks!!
What to plant with Hydrangeas?
I don't know what your natural soil pH is, but if you need to adjust it significantly in order to get the flower color you want, it's more advisable to put the hydrangea in a pot. It's much easier to get (and keep!) the right pH in a pot, but if you're trying to make changes to your soil's natural pH it's going to take a lot of effort to get and keep it where you want it. That being said, red/pink color requires more basic (higher) pH, and blue requires more acidic (lower) pH. Around neutral I'm not sure what color they'll be, but more likely closer to the pink side than to blue. Personally I would keep them on the red/pink side--given the name of the cultivar, they were specifically bred to look nice when they're on the higher pH side, so they may not have that great of a blue color. If you want nice blue's, go for something like Nikko Blue that was bred to have good blue color.
Companion plants...if you keep the pH close to neutral then you can grow pretty much anything you want, I think your Texas climate would be more of a limiting factor than anything else. As long as you don't go too acidic or too basic I think that'll be the case.
ecrane - thanks for the quick reply... My soil's pH is right around 6.0 - many of my TX neighbors are more alkaline, but I live in a piney wooded area, so I'm guessing that's what has made me more acidic (bushels of pine needles everywhere!). I'm building raised beds, actually for all of my garden plants, as my native soil is solid black clay! I think I'd rather keep the hydrangeas red as well - that's why I bought them (never seen them in red before)... I'm not too worried about finding plants that can take the heat - we've got quite a few Texas natives & other heat tolerant plants that do very well here!
Could you put white hollyhocks with them or maybe some lavender.
Lavender and hydrangeas would look nice together, but they have very different water requirements so I'm not sure they'd be a good combo.