I've had a long, mostly unrequited love affair with blue hydrangeas. I first fell for them during a vacation to Cape Cod and Nantucket, where they bloom like periwinkel bowling balls in front of charming seaside cottages.

I wanted that look at home, but at the time, there weren't really any good Zone 4 options. I tried planting a few Nikko Blues but couldn't get them to bloom at all, much less in the color I coveted.

Then came Endless Summer (www.endlesssummerblooms.com), the hardy hydrangea introduced by Bailey Nurseries with much fanfare a few years back. I bought three on the spot. But after the first season, the blooms always came back pink, no matter how much soil tinkering I tried to do with fertilizer.

It takes aluminum in the soil to produce the blue pigment, according to the United States National Arboretum (www.usna.usda.gov/gardens/faqs/hydrangeafaq2.html). But it also takes a soil pH of 5.5 or lower, or the aluminum will not be available to the plant. Apparently my soil just wasn't acidic enough to produce blue blooms.

Until this year. I planted two more Endless Summers last spring. When their blooms started appearing a couple months ago, they were most definitely blue, with a hint of violet. I've been watching them all season, waiting for the blue to shift to lavender and then pink. But so far, they're staying blue-violet -- even though the Endless Summers right next to them are as rosy pink as always.

I don't know if that patch of soil is slightly more acidic, just enough to tip the difference. Or if they're just a little slower to adjust to their new environment than the plants I put in earlier.

STAR TRIBUNE, Star Tribune

There are color-changing kits now available for Endless Summer -- Color Me Pink and Color Me Blue, but so far I haven't tried them. Have you? How did it work? And what color do you like your hydrangeas?