Hydrangeas are among the most popular ornamental plants in the landscape thanks to their large, showy flower clusters that bloom in shades of white, green, pink, purple, and blue. Native to Asia and the Americas, with proper selection, these shrubs can grow in a wide variety of garden conditions and are suitable for borders, foundation plantings, or even containers.
Types | Noteworthy Characteristics | Light | Soil | Watering | Fertilizing | Pruning | Propagation | Potential Problems | More Information
Types
Several species of hydrangea can be successfully grown in Iowa. Some, like smooth hydrangea and panicle hydrangea, are quite easy and reliable to grow. Others require a bit more care or consideration to grow successfully. Each species has dozens of cultivars to consider, each varying in aspects such as size and bloom color. When the right species and cultivar are selected, hydrangeas can be low-maintenance with reliable and abundant blooms.
Learn more in this article: Hydrangeas for Iowa.
Noteworthy Characteristics
Colorful Blooms
Beautiful BloomsHydrangeas make great additions to the landscape. With good cultivars and species selection, they can provide almost constant bloom from late spring to frost. The flowers of most species undergo a shift in color as the season progresses, often starting out bright green, then developing their characteristic white, pink, or blue, and finally drying to an attractive rosy or brown color.
Great Cut and Dried Flowers
Hydrangea blooms make excellent cut and dried flowers. Occasionally, they will wilt immediately after cutting, but flowers will perk back up after about 12-24 hours in a vase.
Good for Pollinators
Some hydrangeas are great for pollinators. Their flower clusters are comprised of two types of flowers. The showy, sterile flowers often outline the bloom cluster, with small, petal-less, fertile flowers inside. Those clusters made up only of showy sterile flowers are referred to as mophead types and those that have fertile flowers are called lacecap. Lacecap varieties are the only ones that benefit pollinators, and it is common to see bees, beetles, and flies frequently visiting these bloom clusters when they are fully open.
Garden-Sized Plants
Hydrangeas are quick-growing shrubs that often develop into a nice, garden-sized plant. Most species and cultivars range from 3 to 6 feet tall and wide, making them well-suited for most home landscapes.
Light
In general, hydrangeas grow best in partial sun. Locations that receive 2 to 6 hours of direct sunlight and protection from the hot afternoon sun are ideal. As hydrangeas are exposed to more light, especially late-day sunlight, their watering needs go up. As they are placed in deeper shade, their bloom number and size will decrease.
One exception to the part-shade "rule" for hydrangeas is the panicle hydrangea (Hydrangea paniculata). These hardy shrubs perform best in full to partial sun, making them the best choice for landscapes with limited shade.
Soil
Hydrangeas grow best in organic, moist, well-drained soils. Heavy or poor soils should be amended with compost to improve the fertility and drainage. While they may want consistent moisture, hydrangeas will not tolerate wet soils or standing water which can promote root disease issues and poor bloom.
Soil pH is an important consideration for certain species, as it can influence flower color. Big leaf hydrangea (Hydrangea macrophylla) and mountain hydrangea (H. serrata) are two species that will have blue flowers in lower, more acidic, pH levels (below 5.5) and pink flowers in more alkaline, higher pH soils (6.0 and up). Since most soils in Iowa are more alkaline, blue flowering hydrangeas often shift to a pink color. Other common species of hydrangea, such as panicle, smooth (H. arborescens), and oakleaf (H. quercifolia), do not change flower color based on soil pH.
Learn more about lowering soil pH in this article: How to Change Your Soil's pH.
Watering
Hydrangeas are not known to be drought-tolerant plants. Consistent moisture is required for the best bloom and growth. Approximately 1 inch of water per week (provided by the gardener or Mother Nature) is needed. Regular irrigation during dry periods may be necessary to prevent wilting. Shrubs planted in areas with abundant competing tree roots will also require more irrigation. Avoid planting in full sun or areas that receive late-day sun to reduce irrigation needs.
Fertilizing
Hydrangeas benefit from regular fertilization. Apply a slow-release, all-purpose garden fertilizer in spring as new growth emerges. Apply fertilizer around the base of the plant in a band 18 inches wide, approximately 6 inches out from the base of the stems. Lightly incorporate it in the soil.
Learn more in this article: Fertilizing in the Home Garden.
Pruning
Pruning your hydrangea depends on the species being grown. Those species that bloom on current year's growth are pruned differently from those that bloom on previous season's growth.
Those species that bloom on current year's (new) growth include:
- smooth hydrangea (Hydrangea arborescens)
- panicle hydrangea (Hydrangea paniculata)
- remontant* cultivars of bigleaf and mountain hydrangea
Those that bloom on previous season's (old) growth include:
- oakleaf hydrangea (Hydrangea quercifolia)
- bigleaf hydrangea (Hydrangea macrophylla)
- mountain hydrangea (Hydrangea serrata)
- climbing hydrangea (Hydrangea petiolaris)
Learn more in this article: Pruning Hydrangeas.
* Remontant means reblooming and refers to cultivars that bloom on current and previous season's growth.
Propagation
Hydrangeas can be propagated in several ways. Plants root easily from softwood or semi-hardwood cuttings. If branches are long and flexible enough, layering is a potential propagation method. For species with numerous stems emerging from the ground, such as smooth or bigleaf hydrangea, division is a viable option.
While plants grow from seed, this is not always an option for home gardeners. Plants will not be true-to-type when propagated by seed and many cultivars produce only sterile flowers, so no seed is produced.
Potential Problems
Flowers are Pink Instead of Blue
Of all the hydrangeas that grow in Iowa, only the bigleaf and mountain hydrangeas can potentially bloom with blue flowers. The flower color of these species depends on soil pH – blue in acidic soils and pink in alkaline soils. In Iowa, most bigleaf and mountain hydrangeas are typically pink to purplish-pink due to the slightly alkaline nature of our soils. Soil pH must be at 5.5 or lower to reliably get blue flowers, and in Iowa, soil pH is more typically between 6.5 and 7.5.
Adjusting the soil pH is necessary to achieve blue blooms in bigleaf and mountain hydrangea. Planting shrubs with Canadian sphagnum peat moss incorporated in the soil can help to lower the soil pH in the root zone. Watering plants with an acidifying fertilizer can also help. Elemental sulfur can be applied to the soil to lower the soil pH. Conduct a soil test to determine the current pH level and apply the necessary amendments at a rate that will lower the pH to 5.5. Over time, soils will return to their natural state, so regular applications of soil amendments will be necessary to maintain the desired pH.
Learn more about changing your soil's pH in this article: How to Change Your Soil's pH.
No Blooms
Several factors can contribute to reduced or missing blooms in hydrangeas.
- Too Much Shade. Most hydrangea species perform best in partial shade (4 to 6 hours of direct sunlight, avoiding the late-day sun). When plants receive 2 hours of sunlight or less, blooms may be sacrificed. Plant in a location that receives more sunlight.
- Improperly Pruned. For those species that bloom on last year's (old) growth, improper pruning can remove blooming wood and prevent flowers from forming. Be sure to prune properly to avoid removing developing flower buds.
- Improper Water. Hydrangeas growing in drought conditions are often too stressed to produce abundant blooms. Be sure to provide regular irrigation when conditions are dry. Remember that hydrangeas planted in areas with more sunlight or where they are competing with tree roots will require more irrigation.
- Improper Fertilization. Hydrangeas growing in low-fertility soils may not bloom well. Those that receive too much fertilizer will develop abundant vegetative growth, but few flowers will form. Fertilize appropriately to get more reliable flowering.
- Poor Soil Conditions. Plants growing in overly wet or dry conditions may not form flowers. Those that are growing in soils low in organic matter or high in clay may also fail to bloom. Plant hydrangeas in moist, well-drained, and organic soils.
- Not Yet Established. Hydrangeas may not reliably produce blooms for the first two to three years after planting. This is particularly true for oakleaf and climbing hydrangea, but any of the species may experience delayed blooming after planting. Wait and provide good care, and blooms should start once plants are fully established.
- Winter Dieback. Some hydrangea species will regularly die to the ground each winter. For some species, such as smooth hydrangea, this is no problem, as they produce flowers on new, current-year growth. For other species, like oakleaf and bigleaf hydrangea, the flowering stems are killed over winter before they can produce flowers. Be sure to plant winter-hardy species or cultivars that bloom on current year's growth. Provide winter protection for those shrubs that are not reliably winter-hardy. Winter protection can be provided in much the same way as for hybrid tea roses, applying protective materials in late fall (mid to late November) and removing it in early spring (March).
- Poor Cultivar Selection. This is an important consideration for bigleaf and mountain hydrangeas, in particular. For these species, which bloom on old, previous-season growth, selecting a remontant cultivar (one that blooms on both current and previous-season growth) is necessary to ensure flower production in Iowa. Remontant cultivars include those in the Endless Summer®, Let's Dance®, and Tuff Stuff® series, among others.
Aphids
Aphid populations on hydrangea can form on growing points or in flowers. They can often effectively be controled with a forceful stream of water, dislodging the pests.
Japanese Beetle
Japanese beetles feed on dozens of different landscape plants, and hydrangeas are sometimes damaged when they emerge in midsummer.
Learn more about management in this article: Japanese Beetles.
Leaf Spots
While typically disease-free, some leaf spots caused by septoria or cercospora are occasionally observed on hydrangea, particularly bigleaf hydrangea. Learn more about prevention in this article: Plan now, save later: Proactive plant disease management.
Powdery Mildew
While not common, powdery mildew can develop on hydrangea (particularly, bigleaf hydrangea) in wet years or when plants are spaced closely together and/or air circulation is limited. Learn more in this article: Powdery Mildew- Ornamental Plants.