Showy clusters or flowers and attractive foliage make hydrangeas (Hydrangea spp.) an attractive addition to any outdoor space. By growing these gorgeous plants in containers, you can easily move them to meet their light requirements, which varies among the different cultivars. Avoid planting hydrangeas during the height of the summer heat, opting for early summer or autumn whenever possible to minimize plant stress.
Selecting a Plant
As long as you plant it in a large enough container, you can grow any hydrangea in a pot, although some taller growing species may have special growing requirements. For example, climbing hydrangeas (Hydrangea anomala subsp. petiolaris), which are hardy in U.S. Department of Agriculture plant hardiness zones 4 to 8, typically grow 30 to 50 feet tall with a spread of 5 to 6 feet. With their sprawling, climbing nature, the container needs to be placed near a wall or a garden structure to give the plant a surface on which to grow. Compact hydrangeas are particularly well suited to container gardening thanks to their manageable size. Some colorful options include the following:
Mathilda Gutges hydrangeas (Hydrangea macrophylla 'Mathilda Gutges') prefers partial sun exposure. It typically grows 5 feet tall and wide and it is hardy in USDA zones 6 to 9. It blooms with deep pink, blue or violet flowers -- depending on the soil's pH -- from June until first frost.
Little Lime hydrangeas (Hydrangea paniculata 'Little Lime') typically reach a mature size of 3 to 5 feet tall and wide. This showy hydrangea, suited to USDA zones 3 to 9, grows in full to partial sun and blooms with pink-tinged green flowers throughout summer.
Little Quick Fire (Hydrangea paniculata 'Little Quick Fire'), hardy in USDA zones 4 to 8, grows well in full or partial sun. It reaches heights and widths of 3 to 5 feet and it blooms with rosy-tinged white flowers -- regardless of the soil's pH -- from summer through mid-autumn.
Lil' Ruby dwarf oakleaf hydrangeas (Hydrangea quercifolia 'Ruby Slippers') grows 3 to 4 feet tall with a spread of 4 to 5 feet. This versatile cultivar grows in full shade to full sun. Hardy in USDA zones 5 to 9, it blooms with cone-shaped clusters of flowers that start out white and change to pink during the early to midsummer blooming time.
Choosing a Container
Achieving a healthy container-grown hydrangea starts by choosing the best container for the job. Look for a pot with a diameter of at least 18 inches to provide the plant's roots ample room to spread. While stone, terracotta, glazed ceramic and plastic containers are all suitable container materials, the type of pot you use has a direct impact on your hydrangea's watering needs. Unglazed clay and terracotta pots are porous and tend to wick excess moisture from the soil. This makes the pot more forgiving if you accidentally over-water the hydrangea, but it also makes the soil dry out faster. Plastic containers retain moisture in the soil, making them a good choice if you prefer less frequent watering. Regardless of material, ensure the pot has drainage holes.
Potting Mix Tips
In general, use a quality potting mix to plant your container-grown hydrangea. When planting the hydrangea, leave about 3 inches of space between the top edge of the container and the soil level to allow enough space for watering the plants.
If you're growing mopheads (Hydrangea macrophylla) or lacecaps (Hydrangea serrata) -- both hardy in USDA zones 6 to 9 -- you may choose to amend the soil with lime or aluminum sulfate to create the ideal pH level for preferred color. For most of these species, maintaining acidic soils with pH levels between 5.2 and 5.5 yields blue hydrangeas while higher pH levels of 6.0 to 6.2 yields pink hydrangeas.
Watering: Water your container-grown hydrangeas deeply and regularly to maintain even moisture. Check the soil every few days -- or every day during periods of warm or windy weather -- and water the container once the top 1/2 inch of potting mix feels dry to the touch. Water the container by filling it to the top rim, letting the water fully drain and repeating once more to make sure the roots receive adequate moisture.
Fertilizing: Over-fertilizing a hydrangea leaves it more vulnerable to insect damage and can limit its blooming potential. Judith King, author of the website Hydrangeas! Hydrangeas!, recommends using a fast-release 10-10-10 formula twice a year, once in late spring or early summer, followed by a second application a month or two later; don't fertilize after August, as hydrangeas need to prepare for dormancy. For each application, add about a 1 tablespoon of fertilizer to a pot with a 20- to 24-inch diameter; follow label directions for specifics. Gently work it into the top 1 to 3 inches of potting mix and water the pot thoroughly to help get the nutrients to the roots.
Frost Protection: You have several options when it comes to protecting your container-grown hydrangea from the ravages of winter. In general, if you choose a cultivar that is at least two zones hardier than your region, you can leave it in its pot and outdoor location. If, for example, you live in USDA zone 6, the hydrangea should be hardy to USDA zone 4. Another option is to move the container to an unheated, protected spot such as a garage or basement. In either case, check the soil periodically throughout the winter and add water to prevent the container from drying out completely.