Hydrangeas are a genus of deciduous shrubs with a long list of species and cultivars grown in Pacific Northwest gardens; most are summer bloomers with a long flowering season and do best in partial or filtered sunlight with adequate moisture. This large group includes climbing varieties, dwarf cultivars, plants with great fall color, and selections with tolerance for sun and drought. They are also great for fresh cut or dried flower arrangements. Our garden centers regularly stock several different cultivars of hydrangeas and have dozens of varieties on hand by mid-spring. No matter the size of your garden or how much sun it gets, there is a hydrangea for you!
Care & Requirements
Most species of hydrangea are tolerant of full sun if given adequate moisture, but they are not suggested for areas with reflective heat such as against a sunny wall or on a hot deck or patio. The best exposure is east-facing in morning sun with dappled, late day sun or afternoon shade. Hydrangeas will grow in total shade, but often only flower lightly, if at all.
Hydrangea macrophylla cultivars are most sensitive to hot sun, but ‘Glowing Embers’ is fairly sun-tolerant with leaves that resist scorching and flowers that don’t tend to fade in full sun. Hydrangea arborescens ‘Annabelle’ and varieties of Hydrangea paniculata and Hydrangea quercifolia are more tolerant of sun and heat than the macrophylla species.
Hydrangeas grow best when provided with adequate moisture, but they do not like standing water or heavy clay soil conditions. They thrive in cool, coastal conditions, but if grown in sandy soil, watering may need to be done more frequently to avoid leaf scorch. Add organic soil amendments at planting time such as compost, peat moss, or decomposed manure to improve soil and create the rich, moist, well-drained conditions preferred; mulch to keep roots cool and reduce water evaporation from soil surface (G&B Soil Building Conditioner makes a great mulch).
Flower color is affected by the pH of surrounding soil; alkaline conditions produce pink blooms while acidic soil produces blue. White flowers tend to remain white regardless of soil pH. To change pH of soil, one must begin a full season or two before seeing desired results—add lime to become more alkaline or Aluminum sulphate (Hydrangea Blue) to be more acidic. Changing the color can often take a few years to accomplish with more than one application necessary (our native soil tends to be acidic; try a pH test kit for more details and information).
Newly planted hydrangeas need regular watering: 2 to 3 times per week if planted in the ground and most likely daily if in containers. Established plants will grow best and flower more prolifically if given adequate moisture through the flowering period; supplemental watering done weekly during the hottest, driest months will keep plants looking their best. Plants exposed to hot, afternoon sun or reflective heat may show a partial wilt during mid-day sun, but this may not be an indication that they need water (I wilt in hot sun too!). Always check soil moisture levels before watering to avoid overwatering and/or causing disease problems.
Winter hardiness/cold tolerance varies by species and cultivar. Hydrangea arborescens ‘Annabelle’ (USDA zones 3-9) is widely planted throughout the United States due to its ability to tolerate temps below 0 degrees. Most macrophylla types are hardy in zones 6-9, while panicle and oakleaf varieties are slightly more cold-tolerant.
Hydrangeas are relatively insect and disease resistant, but can be prone to fungal diseases such as powdery mildew or leaf spot if grown in poor conditions; some newer varieties have been bred for increased disease resistance. Aphids, spider mites, and caterpillars are the main pests and can all be easily handled with a basic insecticidal soap or with Captain Jacks Dead Bug.
Ideal planting times are spring or fall to give the plants adequate time to establish healthy roots before summer’s heat and dry conditions. Fertilizing is generally done at least twice each year: once in early spring as new growth begins and again in late May or early June as flower buds appear and bloom cycle begins. A slow-release organic fertilizer such as G&B All Purpose is preferred over a synthetic such as 10-10-10, which often causes rapid growth leading to weak stems and floppy flowers.
Faded flowers, once no longer attractive, are best removed in fall when the plant is done blooming; though it is okay to remove a few old twiggy branches to the ground each year or two or prune lightly to retain overall shape. Heavy pruning can ruin the flowering for the following year (‘Annabelle’ is the exception and can be cut to the ground in late winter or early spring). Consult an experienced pruner or seek local, expert advice before attempting substantial pruning.
Before major pruning is done, it is important to know the three ways in which hydrangeas flower—those that bloom on new wood, those that flower on old wood, and now there are some newer selections that flower on new and old wood, and therefore require little or no pruning each year. Old wood refers to branches that have been on the hydrangea since the summer before the current season. New wood refers to the branches that will develop on the plant during the current growing season.
- Method 1: For hydrangeas that bloom on old wood (last year’s branches). Prune these plants only in the summer before late August; before they set their bloom buds for the next year. This group of hydrangeas produces flower buds around late August, September, or October for the following summer’s blooms. If those stems are removed (pruned) in the fall, winter, or spring, the bloom buds will be removed and there may be little or no bloom the following summer. Examples: H. macrophylla ‘Nikko Blue’ or ‘Glowing Embers’, H. quercifolia
- Method 2: For hydrangeas that flower on new wood (new branches). Prune these plants in the late summer after they have bloomed. They should not be pruned in the spring when they are preparing to flower because you will cut off the buds. Examples: H. arborescens ‘Annabelle’, H. paniculata
- Method 3: For hydrangeas that flower on both new and old wood. Prune these plants only if they’re getting too large for the space or if you want to remove old flowers. The best time to prune them is after they flower in late summer. If you prune them much beyond late August, you will risk removing flower buds that are developing on current branches. Examples: H. macrophylla ‘Endless Summer’, ‘L.A. Pistachio’
Species & Cultivars
New introductions of hydrangeas have been showing up at garden centers over the last several years, bringing us larger flowers with richer colors, repeat-blooming, and compact growth habits—finally! If you’ve been wanting a hydrangea, but don’t think your garden has enough space, you are in for a surprise!
Bigleaf Hydrangea (Hydrangea macrophylla) is a fast-growing, rounded shrub that begins blooming in early summer with flowers frequently lasting until fall. Flower clusters may be rounded as in the mophead styles or somewhat flat like lacecaps. Old fashioned varieties flower on previous year’s growth (old wood; prune after flowering) while newly developed “next generation” cultivars bloom on both old and new wood. Size and flower form/color vary by cultivar, but on average 3-6 feet tall/wide. Best in dappled sun or partial shade with regular moisture; flower color on some cultivars is affected by the pH of the soil in which they are growing (acid soil = blue, alkaline = pink). White flowers tend to stay white.
‘Niko Blue’ is an older, classic variety with giant blue flowers that rapidly grows to at least 6 feet tall/wide. For a smaller growing variety suitable for containers with limited space, try ‘Pia’ (2-3 feet tall/wide). ‘Glowing Embers’ is a compact grower to 4 feet tall/wide with purple-blue colored flowers in acidic soil conditions; foliage and flowers are tolerant of sun without burning or fading. ‘Lanarth White’ has a lovely lace cap style bloom in pure white on a plant that can grow to 6 feet tall/wide. The ‘Cityline’ series are of the next generation and are bred to be more compact (1-3 feet); try ‘Cityline Berlin’ or ‘Cityline Paris’. The ‘Endless Summer’ collection offers classic looking hydrangeas with re-blooming, next generation qualities.
Panicle Hydrangea (Hydrangea paniculata) is a fast-growing, large shrub with late summer cone-shaped blooms in white or ivory; blooms last a long time on the plant and often change colors as they age —usually finishing with shades of pink. Best used in borders, though occasionally grown as a standard in tree form; can also make a nice privacy screen or hedge. Best in dappled or partial sun, but can take full sun if given adequate moisture.
‘Limelight’ begins blooming in mid-summer and doesn’t stop until frost, has large, soft lime-green flowers that turn creamy white and later blush to pink, and grows 6-8 feet tall/wide. ‘Little Lime’ is a newer, compact version which grows 3-5 feet tall/wide. ‘Vanilla Strawberry’ features huge cones of white flowers that appear in mid-summer and gradually change to pink from the bottom-up, giving the effect of a large strawberry with cream on top; grows to 6+ feet tall. ‘Strawberry Sundae’ is a compact selection of ‘Vanilla Strawberry’ growing only 4-5 feet tall. ‘Quick Fire’ blooms earlier than most other panicle types and ‘Diamond Rouge’ has flowers that begin white and then turn a dark shade of red/purple as they age, providing months of stunning color.
Climbing Hydrangea (Hydrangea anomala sub. Petiolaris) is a fabulous self-clinging vine for growing up brick, stone walls, arbors, trees, or any structure. Slow to get established, this vine will take off after a few years and can scale heights of up to 60-80 feet, but can be maintained at smaller sizes. Late spring or early summer lace-cap style flowers are white and lightly fragrant; older stems develop a peeling texture and a cinnamon color, adding winter interest. Can grow in full sun or shade with adequate moisture; best on east or north exposures. ‘Miranda’ has gold variegation on leaves.
Smooth Hydrangea (Hydrangea arborescens) is a rounded shrub with enormous white flowers (up to 12 inches across) blooming June through September. Grows 3-5’ tall and wide and is best cut back in late fall or early spring; blooms on new wood. Best in dappled sun or part shade, but will take sun with sufficient moisture. ‘Annabelle’ is a cultivar with exceptionally large flowers and is resistant to slug and snail damage.
Oakleaf hydrangeas (Hydrangea quercifolia) are upright, coarse textured, large shrubs with oak leaf-shaped foliage. Later blooming than macrophylla types, the flowers tend to be cone-shaped and creamy white as they emerge in mid-summer, then slowly age to shades of pink towards fall. The leaves turn shades of orange, red, and burgundy in autumn and bark peels with maturity, adding seasonal interest. Oakleaf hydrangeas grow best in dappled or partial sun, but can tolerate full sun if given plenty of water. ‘Snow Queen’ is standard sized, growing to about 6 feet tall, while ‘Pee Wee’ and ‘Munchkin’ are compact dwarf cultivars at 3-4 feet tall and ‘Ruby Slippers’ is more mid-sized and has white blooms that quickly turn from pink to rose colored; flowers are held upright on a full, compact bush.