Hydrangea arborescens - the smooth hydrangea or sevenbark - is a species of flowering plant in the family Hydrangeaceae native to the eastern United States.
It is a medium-sized, deciduous shrub up to 3 m (10 ft), with opposite, serrated, ovate, 8 to 18 cm long leaves with glabrous lower surface or with inconspicuous fine hairs, and showy flowers in a corymb.
The stem bark has a peculiar tendency to peel off in several successive thin layers with different colors, hence the common name "sevenbark".
It is often cultivated for ornamental use. Cultivars include 'Annabelle’, the best known cultivar of this species and one of the most cold hardy of the hydrangeas, or the cultivar 'Grandiflora' which has flowers that resemble snowballs.
Sowing & planting
100 - 300
5 - 7
Identify my smooth hydrangea
This description concerns the hydrangea, - Hydrangea macrophylla - which is a deciduous shrub with a dense foliage forming a large ball 1 to 2 m high.
The opposite leaves can reach about fifteen centimeters in length, hence the term macrophylla, from the Ancient Greek makros, "tall" and phyllon, "leaf". They are simple, membranous, orbicular to elliptic and the apex is acuminate. They are generally serrated (teethed).
The inflorescences are cymes of corymbous cymes, positioning all the flowers in a plane or on a hemisphere or even a whole sphere in the cultivated forms. The flowers have colors ranging from pale pink, fuchsia red to purple blue, depending on the acidity of the soil and the presence of aluminum ion.
Plant my smooth hydrangea
Hydrangea generally love acidic soils - they're known as ericaceous plants. But don't panic if your soil isn't particularly alkaline — we've seen hydrangeas that do great in neutral soil. If worst comes to worst, you can either enrich the soil to make it acidic or simply grow your hydrangeas in a pot!
Plant it in April or at the beginning of autumn. Hydrangea enjoys soft sun or a semi-shaded exposure — it prefers have a north-west orientation.
Hydrangea can be planted in groups, in flowerbeds, as hedges or as borders. It'll also be happy to live in a pot on your deck or balcony.
Unpot the plant. Carefully disengage the roots from each other by making sure they don't cross. Put the root ball in a bucket of water to rehydrate the plant.
Dig a large hole, about half a meter wide, then crumble the soil that you dug up and mix it with ericaceous compost. - about 1/3 soil for 2/3 erircaceous compost. You can also add a little sand and potting soil if you happen to have any at hand.
Place your plant in the middle of the hole while taking care to spread out the roots at the bottom. If your soil is too chalky, you can put a geotextile fabric at the bottom of the hole in order to create a sort of pit ericaceous compost.
Next, fill the hole with ericaceous compost, lightly tamp the soil, and water generously.
Mulch my smooth hydrangea
If the hydrangea had a favorite mulch, it would be bark and pine needles! They provide the acidity that the plant is crazy about. A mineral mulch is also possible, if you have any pieces of slate, break them into little shards that you'll be able to use as a layer.
Otherwise, mulch with compost especially for young plants' first years.
For young plants, during the first two winters and in the coldest regions, it is wise to protect them with a mulch made of wood or dead leaves.
Water my smooth hydrangea
Water generously and often in spring and in summer for the first year, a little less the second, and then mostly during high heat periods and that is all: outside of particular conditions, your ground-planted hydrangea will manage very well on its own (rainwater is gentle which is perfect!)
If your hydrangea is potted, you must think about it from time to time. Rather than watering the pot for long minutes, completely immerge it in a basin while you water the rest of your plants!
One thing: you can provide small basins at the base of the shrubs and then spread out a 10 cm thick layer of mulch.
In the spring, water in the morning, and in the summer, in the evening after the sun has set.
A small problem when watering: if your tap water is too hard, your plant won't appreciate it as much! A simple solution is to collect rainwater, but that isn't only an available option for everyone... If in doubt, add fertilizer for heather from time to time to help solve the problem.
Fertilize my smooth hydrangea
If the soil is too calcareous, your hydrangea may begin to turn yellow and show other signs of fatigue — you must enrich the soil with regular additions of compost and mulch. You can also provide simple supplies of lye from time to time by spreading wood ash. Another simple and natural possibility: dried banana! Cut the banana peel into small pieces and bury them at the base of the plants: it will provide phosphorus and potassium.
For potted plants, consider making these additions even more regularly!
Repot my smooth hydrangea
Your potted hydrangeas will appreciate freshly turned earth every 3 to 4 years!
Repot at the end of winter.
Take the root ball out of the pot by hitting it against the edge. Set the root ball down on its side, then with a sharpened knife, cut the lower third of the root ball: the root system is fine and dense enough that it is easy to reduce the size.
Then remove the crown from the circumference, so the root ball is half the size it was.
At the bottom of the pot, place a layer of gravel for draining, and repot the plant in a mixture of soil and ericaceous compost with a little bit of sand. Finally, tamp down and water generously.
A few days later, you can carry out some light pruning to clear out the center of the plant.
Prune my smooth hydrangea
A pruning which is absolutely mandatory if you want a spectacular flowering!
You can prune at the end of winter, ideally between mid-February and mid-March. The flowers of the hydrangea grow on the wood of the previous year: so it is important not to cut everything, otherwise you will not have flowers at all! First look for the oldest stems, dead or possibly a little brittle.
Observe the shape of your hydrangea: the pruning should aim to give a balanced shape to, and to allow the light to penetrate inside.
Remove the dead wood, and cut the stems you have chosen to eliminate.
Then trim the deflowered stems that you want to keep, just 1 centimeter above the first bud below the flower, or possibly the buds just below.
Propagate my smooth hydrangea
If you've never tried taking cuttings and you're only going to do it once, try it with your hydrangea! Foolproof and fun to do!
The most opportune time to take cuttings is when your hydrangea is in bloom, between August and the end of September.
Choose a nice, hardy stem that grew the same year and hasn't yet flowered. Cut it off 20 cm from the tip, keeping the main part of the stem. Prune again at the tip and the bottom, and cutting just below a pair of leaves at both locations.
Carefully remove the pair of leaves at the base of the cutting, only leaving the higher leaf pair.
Plant the cutting in a mixture of potting soil and sand, or a special potting soil made specifically for cuttings.
Space your cuttings between 5 and 10 cm apart.
Plant them in the shade and keep the substrate just cool, no colder.
Keep them sheltered from the frost all winter long — you may plant in open soil come spring.
You can also collect the seeds of your hydrangea and sow them in open ground starting in March. Watch out, surprise! The seeds will not reproduce an exact copy of the plant that produced the seeds.
Check on my smooth hydrangea
Hydrangea is extremely resistant, but it can still sometimes fall victim to diseases.
Keep an eye on the stems — if you find little white balls, it's almost certainly scale insects. These insects hang off the underside of leaves and suck sap from the plant, appearing towards the end of May. A hot and humid preseason provides a good environment for them.
As soon as you seen signs, remove the insects manually with a soapy, wet rag. You can then spray them with a solution of water (1 liter) with one teaspoon each of liquid black soap and 90° alcohol.
Be careful, in hot and humid weather, a white felt on the back of the leaves might also indicate a powdery mildew attack.
Regularly spraying the foliage with a mixture of water and skim milk often helps to eradicate this fungus.
Mix 100 ml skim milk with 1 liter of water and apply with a spray bottle weekly. Choose skim or semi-skim milk to avoid the nasty odors created by decomposing milk fat.
Take care of my smooth hydrangea
Would you like to have blue-toned flowers, or even fully blue ones? It's possible, but completely dependant on the acidity of the soil. Good to know — despite your best efforts, most white hydrangeas will stay hopelessly white.
To acidify your soil, make regular additions of ericaceous compost and water your hydrangeas with an aluminum sulfate solution. You can find these solutions easily at a garden centre, and you may use them all winter long, until April.
A tip for the wise gardener — if you'd like to use a more natural technique, mix crushed slate into your substrate or even use it as mulch before winter!