Gardening 208: All About Hydrangeas

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Heavenly. Happy. Harmonious. Hypnotic. Hydrangeas.

 

Long-lasting flowers and bold textured leaves lend to a universal love of hydrangeas. Whether you have a wild cottage garden or a manicured formal garden, these shrubs have a multitude of uses in the landscape. There are many species of hydrangeas and most perform best in part shade. There are a few, however, that will tolerate full sun even in Idaho’s desert.

These summer bloomers give in abundance and many transform in color throughout the season. Hydrangeas even offer fall and winter interest, which add to their versatility, beauty, and charm.

The name hydrangea comes from Greek origins. Hydor (water) and aggos (jar) refers to the cup-shaped fruits they produce. The name is also helpful as it alludes to this shrub’s high water requirement. Hydrangeas require more water than most garden plants and are intolerant of drought. They prefer moist, well-draining soil and it is best if they do not completely dry out between waterings. Watering deep into the root zone will give your plants the best success, and watering a hydrangea planted in the shade will require less watering than one planted in the sun.

With that said, let’s breakdown the six most common hydrangea species found in the Treasure Valley.

Hydrangea Species:

Photo of a white hydrangea arborescens

H. arborescens – Smooth hydrangea

Height: 3-5’
Spread: 3-5’ and larger

Smooth hydrangeas are often broader than they are tall at maturity and keep a loose mounded form. Fertile flowers emerge an apple green color in tight, round clusters and mature to white. Flowers bear in June and bloom until August. It is best to deadhead flowers as they begin to fade to brown due to lack of ornamental value.

Use as a hedge, boarder, natural, or mass planting in part shade.

H. macrophylla – Big leaf hydrangeas

Photo of blue hydrangea macrophylla

Photo of pink hydrangea macrophylla

Height: 3-6’
Spread: 3-6’

Big leaf hydrangeas have two bloom shapes: mophead and lacecap. Mopheads have full and round clusters. Lacecaps have small, fertile flowers that resemble buds in the center and large, sterile flowers that blossom around the outer edge.

Macrophylla hydrangeas are the well-known classic blue and pink varieties, and their color is affected by soil pH levels. Strongly acidic soils produce blue flowers and neutral to alkaline soils produce pink flowers. To keep flowers blue, apply aluminum sulfate to the soil. To keep flowers pink, apply lime. Soil treatments must be done well in advance before flowering, such as late autumn or early spring. White flowers will remain white.

Most of these hydrangeas bloom on old wood, but Endless Summer® hydrangeas changed the game when they were introduced with flowers that bloom on old wood and new wood, marketing themselves as rebloomers.

In our climate, these hydrangeas prefer morning sun and dappled afternoon shade, and they cannot withstand dry soil. Use these in cutting gardens, mass plantings, and boarders. Dried flowers are also nice for arrangements.

H. serrata – Mountain hydrangea

Photo of light pink hydrangea serrata

Height: 2-4’
Spread: 2-4’

Bloom color is influenced by soil pH levels much like H. macrophylla (see above section for more information on how to maintain blue or pink flowers). In fact, H. serrata is very similar to H. macrophylla and used to be classed as a subspecies. This shrub is more compact and has smaller blooms and leaves. Blooms are primarily lacecap. This hydrangea prefers moist, well-draining soil with a high percentage of organic matter and appreciates dappled shade.

H. paniculata – Peegee, Panicle hydrangea

Photo of white hydrangea panciculata

Height: 10-20’
Spread: 10-20’

Size is variable and often less than 10’, especially in dwarf cultivars.

The easiest to grow, most adaptable, and most sun tolerant of all hydrangeas. In our climate, panicle hydrangeas appreciate six or more hours of sun as it encourages the most flowers and strongest stems. Don’t be afraid if they get some afternoon shade, though, as they will appreciate the respite from Idaho’s intense UV rays.

Panicle hydrangeas are commonly grown as multi-stemmed shrubs but can also be trained or grafted to grow as small landscape trees. Blooms are pyramidal panicles and begin as creamy white which fade to pink or red. The color is genetic and not influenced by pH levels in the soil, therefore, it cannot be altered.

Flowers are wonderful for pollinators and are nice as fresh cut or dried in arrangements.

H. quercifolia – Oakleaf hydrangea

Photo of white hydrangea quercifolia

Height: 4-6’
Spread: 8-12’

Boldly textured and deeply lobed, the leaves resemble those of oaks. Spectacular fall color ranges from bronze to purple to crimson. The foliage alone is enough to justify adding this hydrangea to your landscape, but it does not end there. Eight-inch-long flowers are creamy and fragrant which fade to pink or red in late summer.

This is the most “drought tolerant” of all hydrangeas once established, but do not let it dry out completely between your watering schedule. Plant in an area with morning sun and afternoon shade. Use as foundation plantings or mass plantings in a naturalized area. Dwarf cultivars are nice as specimen plants.

H. anomala subsp. petiolaris – Climbing hydrangea

Photo of white hydrangea anomala subspecies petiolaris

Height: 30-60’
Spread: Variable

This vine is slow to establish but becomes quite vigorous once roots set in place. Ariel rootlets develop along stems and is an effective climber on walls, fences, and arbors. Size can be maintained at lower heights and overly vigorous growth should be pruned out after vine is well established.

Flowers are white lacecaps, and attractive reddish-brown exfoliating bark appears once vine is mature.

This is an extremely versatile vine that loves part to full shade.

Pruning:

It is important to know what kind of hydrangea you have before you prune. Some hydrangeas flower on old wood and others on new wood. Old wood bloomers produce flowers on stems that have been on the hydrangea since the previous season. New wood bloomers produce flowers on stems that appear during the current season.

New Wood: Cut these back in late winter or early spring when hydrangeas are dormant and before the new growth develops. For bigger flowers, cut stems down to just a few inches above the ground.

Smooth hydrangea (H. arborescens)
Panicle hydrangea (H. paniculata)

Old Wood: Prune after flowers start to fade in late summer. The shrub will have a chance to produce new growth which will turn “old” where next year’s flower buds will form. Use sharp, clean pruners, and make cuts just above a set of leaves.

Big-leaf hydrangea (H. macrophylla)
Mountain hydrangea (H. serrata)
Oakleaf hydrangea (H. quercifolia)
Climbing hydrangea (H. petiolaris)

To get big flower clusters, reduce the number of stems. To get flowerheads at different levels, cut stems at various heights. Whether you have an old wood bloomer or a new wood bloomer, it will always benefit your shrub to remove any dead, diseased, or damaged branches.

Hydrangea Selection

It may be difficult to narrow down the type of hydrangea you’re looking for, after all, there are hundreds of cultivars within each species. The good news? Franz Witte has a wide selection of hydrangeas, and our trusty staff is always around to give you the best recommendations and advice.

Before beginning your hydrangea search, here are a few questions to consider:

How much shade does the area you want to plant in get? What is the soil like? How big is the area? Is it right next to the house? Is there existing irrigation or an easy way to get water to the area? Are you going to use the flowers for cutting or drying? What colors do you like?

Answering these questions can really help narrow down the search. If you see a hydrangea in someone else’s landscape that you like, take a picture and bring it into the garden center. Hydrangeas bring a wonderfully diverse and textured presence to the garden, and not knowing where to start shouldn’t keep you from adding one (or a few) of these shrubs to your landscape.

By Riley Rehberg

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