The color is the result of the soil pH that the potting medium has. If you change the potting mix or you plant it on the ground, the color will adjust to the "new" soil pH. It seems to be a florist hydrangea, commonly sold by florist and grocery stores. In order to maintain the color, it may be useful to know what the exact soil pH is so you can amend the soil if the soil pH changes. There are some soil pH kits sold at nurseries or via the Internet that can help you. The cheap ones are ok but are not as accurate as you need. Look for kits that give you a numeric result. If the numeric result increases to a bigger number, the soil mix has turned alkaline (or less acidic) and you will need to amend the soil mix to acidify it a little. On the other hand, if the soil pH were to decrease to a smaller number, the soil mix has turned more acidic (or less alkaline) and you wil need to amend the soil mix by adding some garden lime. It is easier to make these changes if the plant is grown in a pot... harder if grown in the ground.

Thanks, Luis. I never buy garden plants from the grocery store, but was so smitten by the lovely flower form and the white eye of this hydrangea. And of course, the color. And I figured the grower was acidifying the soil to some degree, so I went back to Trader Joe's to check on more of this variety. They apparently had just gotten in another large delivery. Sure enough, 'Oslos' in every shade of blue to pink, so they were simply messing around with the soil pH, but good to know this is a variety that WILL blue up. I also had a very nice chat with the grower as well. She assured me it will do well outside - her yard is full of them and she lives up in N. California, so climate is not too terribly different as far as hydrangeas go. Plus, my hydrangeas (Incrediball and possibly an Annabelle, was here when I moved in) do very well here, as do everyone else's hydrangeas as long as they're given afternoon shade (east or north exposure).

My soil is 6.2 to about 6.7, we're a bit on the alkaline side, so my hydrangeas are pink (I'm a Master Gardener). I remember when I was little growing up in Vancouver, BC, my grandmother had the most gorgeous and huge hydrangea bushes that were full of lovely blue, blue flowers, due to their much more acidic soil.

For us, actually, using aluminum sulfate works better to blue up those hydrangeas that will turn blue. Usually, folks will plant Nikko Blue here, and then treat with aluminum sulfate. You can acidify the soil with soil sulfur, but you still need to apply aluminum sulfate to get them to turn blue. Otherwise, you end up with the color I picked up, sort of a violet :-) So, I'll probably never get these to be blue, but I'll experiment a bit to see if I can at least get them to a pretty violet.

Thanks for the tips, hoping more to see if anyone has grown this new variety, and how they do in the garden. My Annabelle tends to develop mildew in the location I'm going to be planting these 'Oslo' hydrangeas, the Incrediball is still lovely and full of blooms. I think I'm going to yank out the Annabelle, pick up 3 my Incrediballs, and plant both the Anabells and the Oslos along the back side of the house where they do so well.

Patty S.

Good luck Patty! I know about some of those grocery specimens. I do not think I will ever forget one I saw while visitng a relative in South Carolina. It was just gorgeous! If I had been driving, I would have bought one and bothered to maintain the soil pH at the level it needed to produce those blooms.

Thanks, Luis! I, too, have always appreciated and admired the grocery store hydrangeas, but figured they really weren't bred for our garden environments, but between our great growing conditions for hydrangeas here near the coast in San Diego county, and the structure and beauty of this 'Oslo', I decided to take a chance. Plus, the price was pretty good, $7.00 for a nicely formed hydrangea. Plus, the chat with the grower, Bay City Floral Company, also helped. I was pretty direct, "This isn't the typical floral specimen that's going to croak when I put it in the ground?" was also reassuring. The only mild negative was that the flower heads might need some support if the plant gets really floriferous. Which is fine by me. We'll see how it does in the powdery mildew department, though. That's the big issue I seem to have with the older varieties here with the amount of marine layer moisture that I can get where I live. If I can get enough soil sulfur worked into the soil, the maintenance of the pH for several years shouldn't be too difficult. Hopefully, monthly applications of aluminum sulfate solution will keep them at least violet :-)

Patty S.