For several reasons, potted hydrangeas are gifts that keep on giving.
First, they are beautiful. The popular choice is a gorgeous sky blue, but there are also hydrangeas bearing globes of white, pink or mauve.
Second, the flowers last. Watered often enough so that the leaves and flowers don’t wilt, hydrangeas look good in the home for many days.
Third, you can keep them. The gift hydrangea, commonly called bigleaf hydrangea or mophead hydrangea, is a shrub for the landscape, where you can plant it once the flowers fade and no longer look so good indoors.
These gift plants have been grown vigorously to create a good show of flowers and foliage. That means the pot is packed with good roots that will help the plant get off to a good start once you select a lightly shaded spot outdoors. It requires good, well-drained soil, meaning that the native clay is improved with compost or good topsoil.
Once you take the plant out of the pot, by turning it over and gently nudging it out, you may be surprised to see a tight web of roots wrapped around the outside of the root ball. Growers encouraged this to get the plant to an attractive size. But as you prepare to plant, loosen up these tightly wound roots. Use the tip of a trowel or pocketknife to pull some of these roots away from the sides and bottom of the plant. This seems destructive, but it will help the plant get established in its new place. The roots will grow into the surrounding soil instead of continuing their way around the root ball.
Though the plant seems small in its pot, it is destined to become quite large, usually about 3 to 5 feet over time with a similar spread. So give it space to develop fully because part of its beauty in the landscape is its graceful, oval shape. Don’t stuff it with other shrubs.
These mophead hydrangeas respond to soil pH, meaning the acid to alkaline balance. Acidic soil tends to produce blue flowers because it encourages uptake of aluminum out of the soil. If you like blue flowers, a fertilizer formulated for acid-loving plants such as Holly-tone may be all that is needed to keep the blue you like. A bit of aluminum sulfate spread over the root zone will increase the blueness of the flowers.
A pink hydrangea has been boosted into pinkness with chemicals to keep down the aluminum uptake. Keeping it pink in the landscape will require the addition of lime, about one cup per 10 square feet of ground, that will move the soil to a more neutral or alkaline state.