1. Choose the Right Hydrangea
Only the flowers of bigleaf hydrangea (Hydrangea macrophylla) and mountain hydrangea (H. serrata) can change color. Other types like oakleaf hydrangeas (H. quercifolia) or smooth hydrangeas (H. arborescens) such as ‘Annabelle’, cannot change their flower colors, naturally blooming in white, cream, or dusty pink. These plants are just as full and beautiful, but if your goal is deep pink hydrangeas, make sure you’re planting varieties that can turn that color. Two popular bigleaf hydrangea varieties with gorgeous pink blooms include Let’s Dance ‘Big Band’ ($20, Great Garden Plants) and Endless Summer ‘Summer Crush’.
2. Measure Soil pH
Soil pH naturally ranges from 0 to 14, with 7.0 being neutral. Lower than 7.0 is acidic and higher is alkaline. If you want pink hydrangea flowers, the pH needs to be on the alkaline side. Finding the pH of your soil is quick and easy to do with a soil test kit. A reading above 7.0 means that your hydrangeas should produce pink flowers without you having to do anything else. A reading between 6.0 and 7.0 usually results in purple to pink blooms, and readings lower than 6.0 yield purple to blue hydrangea flowers.
3. Increase Low Soil pH
The best way to increase the pH of your soil is to use garden lime, which is made from crushed dolomitic limestone. Add the pellets to the soil when you plant your hydrangea. Or follow package directions to amend the soil around an established plant. Higher pH levels make aluminum in the soil less available to plants. This element makes the blue color appear in hydrangea blooms.
4. Don’t Forget to Fertilize
Soil amendments, such as garden lime, may change hydrangea flower colors, but they don’t give the plants all the nutrients they need to thrive. Hydrangeas do best when fertilized in early spring as soon as leaves begin to emerge. If you’re growing a reblooming variety like those from the Endless Summer series, add fertilizer again in midsummer after the first flush of flowers to encourage plants to produce another set of flowers. Don’t feed your hydrangeas after July, or it may stimulate tender new growth that’s more sensitive to frost damage. Use a slow-release, all-purpose fertilizer ($22, The Home Depot) to give your plants a steady supply of nutrients over the growing season.
5. Practice Patience
Changing the pH of garden soil takes anywhere from 3 to 18 months. Continue adding garden lime for pink hydrangea flowers according to package directions until the desired color is reached. Maintaining the consistently pink blossoms will require regular applications of garden lime, so it’s a good idea to add it whenever you add fertilizer. Once flowers appear, they won’t change color, so you’ll have to wait until the following year to see a different color resulting from your efforts to modify soil pH.
6. Consider Containers
It can be challenging in yards with very acidic soil to raise the pH enough to get pink hydrangea flowers and keep them up. It’s easier to grow your bigleaf hydrangeas in containers in a good-quality potting mix, which usually won’t have aluminum, so the flowers can’t turn blue.
