How to Plant, Grow, and Care For Smooth Hydrangeas
Smooth hydrangeas are one of the more popular types of hydrangea grown each season. Their compact shrubby nature makes them ideal for areas where you may not want a fully grown, taller plant. In this article, coastal gardening expert and hydrangea enthusiast Jill Drago outlines each step for planting, growing, and caring for smooth hydrangeas.
Hydrangeas are one of the most popular flowering shrubs to plant in gardens. They are easy to care for and provide a stunning pop of color. With a wide assortment of varieties ranging in size, color, and bloom type, there is an option for every gardener!
If you are looking for a hydrangea with a full, round bloom head, look no further than the smooth hydrangea. This gorgeous shrub looks like a vase of flowers. Their stems are longer and hold the large flowers up above the leaves. The green flowers turn into a dazzling white as they mature.
With its elegant charm and tolerance to colder climates, this American beauty ranks in the top choices for many home and commercial gardens. From propagating to maintenance, let’s dig into how to plant, grow, and care for the show-stopping smooth hydrangea!
- 1 Hydrangea Arborescens Overview
- 2 What is a Smooth Hydrangea?
- 3 Why Plant Hydrangea Arborescens?
- 4 Propagation
- 5 How to Plant
- 6 How to Grow
- 7 Popular Varieties
- 8 Pests
- 9 Diseases
- 10 Plant Uses
- 11 Frequently Asked Questions
- 12 Final Thoughts
Hydrangea Arborescens Overview
Plant Type Flowering Shrub
Maturity 2-4 years
Native Area Eastern United States
Season Spring through Fall
Soil Type Well-draining
Plant Height 4-5 feet tall
Plant Spacing 4-5 feet
Exposure full sun to partial shade
Hardiness Zone 3-9
Pests Aphids, Japanese Beetles
Watering Requirements Moderate
Plant With Partial shade perennials
Don’t Plant With Full sun perennials
What is a Smooth Hydrangea?
Hydrangea arborescens is often referred to as smooth or wild hydrangea, and also by sevenbark, which comes from the peeling bark of this shrub. However, its most common name is smooth hydrangea.
They are mounded shrubs that tend to be wider than they are tall. They will grow to about three to five feet tall as well as wide. The flowers are typically green and mature to large white blossoms.
These blossoms are dome-shaped, round on the top and flat on the bottom. However, the plant has been hybridized and there are shades of pink available now.
As the stems age, the bark will begin to peel offering some interest before and after the bloom time. This bark will still be appealing in the winter if you choose to wait to prune until the spring.
The Hydrangea arborescens, is native to the eastern half of the United States. This species gained notice after it was just popping up in people’s yards after being shared by friends and family members. It became an American staple all on its own.
After a bit of hybridizing and marketing, this easy to grow shrub is becoming more popular with more varieties becoming available at garden centers every year.
Why Plant Hydrangea Arborescens?
At first look, you may think that smooth hydrangeas and bigleaf hydrangeas are pretty similar, and you would not be wrong. They both have nice foliage and big ball-shaped flowers.
Bigleaf hydrangea does offer much more in terms of the available variety of colors of the flowers. These flowers could be white, blue, pink, or purple. If you are not happy with that flower’s color it is easily changed by amending your soil.
Smooth hydrangeas have green varieties, white flowering varieties, and a few new pink varieties popping up. These flowers are not sensitive to the pH of your soil and are therefore unchangeable.
This species is hardy in a wider range of zones (3-9) and are very cold tolerant. They also bloom on new wood meaning if you do live in one of these colder zones you won’t have to worry about any winter damage because you will be able to prune it down to the ground either in the winter or spring.
Bigleaf hydrangeas bloom on old wood and their pruning needs to be done right after flowering has finished, leaving any winter damage to be dealt with in the springtime at the risk of losing newly formed flower buds.
Smooth hydrangeas can be easily propagated from taking cuttings right at home. Snip a newer stem that is at least a few inches long with one set of leaves on it. You can use a rooting hormone powder if you choose, or not. Then simply stick it into some growing material! Once your new shrub has rooted you are free to transplant it as you wish.
Hydrangea arborescens has always had a popular variety in ‘Annabelle’, however, more and more varieties are becoming readily available at garden centers. Dig a nice big hole, twice the size of whatever size plant you purchase, and backfill with good quality soil. Allow Hydrangea arborescens enough room to grow by spacing these flowers at least 5 feet apart.
How to Grow
When growing this species, it’s important to make sure that you provide the conditions needed for them to survive and thrive. While they can make great container plants, they are also well situated to grow in all areas of the garden. Let’s take a look at the most important factors you’ll need to consider when growing this species.
Hydrangea arborescens prefers to be planted in partial shade, which is anywhere from 4-6 hours of sunlight. However, it has been noted that these plants can do just as well in full sun if they are given supplemental waterings when the heat of the summer is in full force.
As with all hydrangeas, this species loves to be well watered. Keep your eyes open for drooping leaves, and avoid letting them dry out as they are not drought tolerant.
If you plant them in containers they will likely need daily waterings throughout the summer months. They can be more sun tolerant if they are given adequate water to balance out the extra sunlight they are receiving.
The smooth hydrangea does best in rich, well draining soil that is kept moist. Amending your soil with compost or peat is a great way to improve your soil conditions. Remember, this species does not change color.
This means that adjusting the pH values of the soil and its acidity will not prompt the booms to change during the growing season. You’ll want to stick with other species that produce blue blooms if that’s your goal.
Smooth hydrangeas are hardy in USDA zones 3-9. Because they bloom on new wood, you don’t have to worry about winter damage too much since you can just prune everything back to the ground in the spring.
Hydrangeas love a basic spring and fall fertilizer. A fertilizer or a fertilizer meant specifically for acid-loving plants would be a great option, too. This species has such large flowers it is important to not weaken their stems.
Over-fertilizing will push growth which could potentially cause the stems to grow longer than they would on their own. The end result of over-fertilizing would be weakened stems that will lean with the weight of the flowers.
Smooth hydrangeas are very low maintenance… dare I say the easiest species to take care of? Aside from pruning, they don’t require any additional maintenance.
Deadheading is an optional task, however, if you do remove your blooms be sure to bring them inside so you can enjoy them for a little bit longer. Their flowers are very pretty when they are dried and hold their shape very well.
Weeding around your shrubs and mulching will help to keep your plants well-watered and able to take up the fertilizer that you have provided.
Hydrangea arborescens blooms on new wood. This means that the flowers bloom on growth that is formed in the spring. In other words, you are free to prune them right to the ground in the fall or in the early spring before any growth appears.
If you would like to control their growth habits, you can cut the stems to knee height. This will offer some stability for the new growth that will be coming in the spring and give you a more upright look to the shrub.
There are many popular varieties of smooth hydrangeas, including the extremely popular ‘Annabelle’ and ‘Incrediball’ cultivars. Both of these hydrangeas are very popular for their beautiful white blooms. Let’s look at some of the more popular shrubs from this species.
This is one of the most popular hydrangeas around, let alone the most popular smooth hydrangea. It has been around since 1910 and is still very well-loved today. This variety of hydrangea has massive white ball-shaped flowers that dance above the long lean stems.
‘Annabelle’ is a quick grower and will reach its full size of 5 feet in no time! Be sure to give this shrub plenty of room to grow. Plant ‘Annabelle’ on its own in the garden or as a hedge. This plant loves to be cut to the ground and is a dependable bloomer.
‘Incrediball’ is a hybrid of ‘Annabelle’ and other Hydrangea arborescens varieties with the goal of stronger, more supportive stems. The hybridizers were successful and ended up with an amazing plant with very strong stems that will support its flowers and remain upright even after a period of heavy rain.
‘Incrediball’ is a little bit smaller than ‘Annabelle’ growing to 4 feet. However, its flowers are even bigger reaching up to 12 inches across. These large flowers are a bright white for most of the season but fade to green and hold their color through a frost.
This shrub can be used anywhere in your garden from a woodland edge to a perennial garden, and don’t forget your cutting garden!
Here we have a smooth hydrangea that bears pink flowers! You can depend on ‘Invincibelle Spirit’ to behave and look very similar to ‘Annabelle’. Its stems are sturdy, but not quite as sturdy as ‘Incrediball’ and you may have some flopping branches after a rainstorm.
These pink flowers open as a very deep pink and slowly bleach out in the sun giving the flowers a really pretty speckled appearance since the petals don’t all fade evenly.
This variety has since been improved upon and you may find plants labeled as ‘Invincibelle Spirit II’ or ‘Invincibelle Spirit III’. The improvements made to these plants were mainly to strengthen the stems. There are other colored hydrangeas in the ‘Invincibelle’ line, including a beautiful red variety.
‘Seaside Serenade Bar Harbor’
‘Bar Harbor’ is a compact version of the famed ‘Annabelle’. It has been bred to have strong stems that withhold the winds and rains of the summer seasons. Growing at a moderate pace this hydrangea will max out at four feet tall.
This is a great hydrangea to use in a container since it is a bit smaller than the others. The dome-shaped flowers bloom green and fade to a creamy white that will cover your hydrangea and last all season.
The ‘White Dome’ hydrangea grows from four to six feet high and wide, making it a substantial addition to your gardens. ‘White dome’ has unique six to ten-inch cloudlike foamy flowers. These flowers are white and turn pink as they age. This variety would make a really nice hedge or would be well used as a mass planting in the back of a perennial garden.
Hydrangeas in general are pretty tough plants that are not taken down easily by pests. However, smooth hydrangeas can have issues with some of your run-of-the-mill garden pests.
Occasionally you could find deer nibbling on the leaves of this species. But for the most part, wildlife will not be an issue for this species. Aphids, beetles, and spider mites are insects that are commonly found on all hydrangeas.
Aphids and spider mites can be removed by hitting them with the spray of your hose. Japanese beetles can be knocked into a bucket filled with soapy water by hand. You can also opt to use insecticidal soap to control these pests without harming any pollinators.
This species can have some difficulty with fungal diseases. Diseases you may find on your smooth hydrangeas are: leaf spot, powdery mildew, botrytis blight, and root rot.
To prevent these diseases from the start it is important to remove infected leaves from the plant and keep the soil around the plant free from fallen leaves and weeds.
Hydrangea arborescens can be a wild and unruly grower compared to other species. With this being said, it is lovely planted in a mass or on a woodland edge where its whimsical habit can be truly appreciated.
When they are found growing wild they tend to be in rocky areas or slopes. WIthing your landscape you could benefit from these traits by using them on a hill that needs some containment, or in a naturalized area of your yard.
Don’t forget to save those flowers, they make excellent dried flowers.
Is this species considered invasive?
This species is not considered to be invasive in the United States. However, they do produce suckers and can spread easily throughout your gardens. Suckers are essentially branches that grow from the roots near the base of the trunk.
This characteristic is what makes them so useful for erosion control. Don’t worry, they will not engulf the other plants in your gardens if you space them appropriately. These shrubs should be planted at least 5 feet apart.
What should I plant with them?
I love when Hydrangea arborescens is planted as a hedge, it really offers a nice cottage vibe to a garden. If you are looking to add other plants into the mix, look for other plants that are native to the United States. These plants will require the same types of growing conditions, and will attract the same types of pollinators. Some plants that could be used in this way are bee balm, black-eyed susan, or garden phlox.
Of course the typical hydrangea companion plants of coral bells, ferns, hostas or other shade loving perennials would always fit the bill.
I think it’s practically impossible to not fall in love with the smooth hydrangea. Its flowers are so rewarding, and their beautiful blooms will captivate your garden guests each season. They attract pollinators and are quite easy to take care of. Once you have these blooming in your garden, you will wonder why you hadn’t planted them sooner!