Althea, also called Hibiscus or Rose of Sharon, is a very decorative shrub.
A list of Althea facts
Name – Hibiscus syriacus
Family – Malvaceae (mallow family)
Type – shrub
Height – 3 to 13 feet (1 to 4 m)
Exposure – full sun, part sun
Foliage – deciduous
Flowering – July to November
Caring for this plant, from planting to blooming and including watering and pruning, is easy and this will give your althea magnificent flowers.
Whether you plant it in a pot on a terrace, deck or balcony, or directly in the ground in a shrub and flower bed, Althea deserves particular care upon planting to ensure it grows and blooms well.
Planting althea in pots
All year round, the shrub must be planted in a soil mix designed for flowering plants, for planting, or any universal soil mix.
- Althea needs a pot that is large enough, this will enable it to grow well as seasons come and go.
- A bed of gravel or clay balls at the bottom of the pot will guarantee sufficient drainage. This helps prevent roots from wallowing in sitting water at the bottom of the pot.
- The pot must have a hole at the bottom for excess water to drain away.
- Repot in spring, at least every second year (3 years is also fine occasionally), in a pot that is slightly larger than the previous.
Planting althea in the open
Prefer planting in fall or spring if you have purchased the shrub in a pot or a container.
- Choose a sun-bathed area, sheltered from stronger winds.
- Watering often during the first year after planting is important for Althea.
- Follow our advice on planting shrubs.
Propagating althea through cuttings
Cuttings are very easy to perform in spring for althea.
Simply keep cut stems in a vase with water, and plant as soon as a few roots appear.
When to prune Althea
At the beginning of spring, towards February-March, it is time to prune your althea. Early spring pruning still gives the shrub time to produce flowers in the summer of that same year.
Althea blooms on new growth, so you can prune every year.
However, try to avoid pruning late in the season, since this would tend to reduce blooming.
How to prune Althea shrubs
- Remove all branches that grow inwards so that the shrub can filter light through the inside.
- After that, cut remaining stems back by about ⅔, just above an outward-facing bud. This means 1/3rd of the branch remains on the tree.
Diseases and pests that attack Althea
In hot weather, Althea leaves quickly lose their firmness and start drooping over.
- This is a sign that the shrub needs watering.
- Water abundantly with rainwater.
- Ensure the soil drains well, though, since even in warm weather, wet soil will lead roots to rot.
If this occurs very often, then you’ve planted the shrub in a spot that is too hot and dry for it. Try protecting it with a taller neighboring plant, moving it to a cooler spot, or use a shade veil that dampens the sun out during the hottest hours.
All the leaves drop off within a few days
This, on the other hand, is due to excess water.
- Don’t water until the soil surface feels dry to the touch.
- If it’s still moist, cool, and rather on the sticky side instead of feeling dusty, don’t water yet.
Flowers are stunted, teeming with insects, and are covered in a sticky mess
This is typically due to aphids and to their shepherds, ants.
If the bugs look like tiny wisps of cotton, then it’s certainly mealybugs.
Flower buds drop before opening up
Dry air is what causes flower buds to drop before opening up. If in a pot indoors, avoid setting the plant near a radiator or large, sun-filled window.
- Try one of these many ways to increase air humidity around potted plants.
All there is to know about althea
Althea, also part of the Mallow family, is very certainly one of the most beautiful flowering shrubs. Not only is it well suited to any garden, but it also does great on terraces and balconies. Another name for this plant is tree mallow.
Even if this shrub prefers warm climates, several varieties are perfectly adapted to our harsher climates, like Hibiscus rosa sinensis or Hibiscus syriacus.
The numerous cultivars available in garden stores and county fairs allow for many shapes and colors, and each is more beautiful than the next.
Whatever the configuration – hedge, flower bed or stand-alone – althea will enchant you with the beauty of their flowers.
Its blooming is very generous, in that it is both opulent and constantly renews itself from July to October and even November if the weather stays mild.
Smart tip about althea
If it freezes in your area, it is highly recommended to winterize your plant with horticultural fleece as early as November!
ISO double pink Althea cutting or rooted small plant.
Hi, to make sure you get the same plant, cuttings is the way to go. Since it’s a double flower, getting seeds is very rare (if not impossible). Moreover, any seeds would be a cross-pollination with another variety that is likely not double-flowered. As a result, any seed from offspring would be different from the parent plant, and probably not be double-flowered anymore.
In garden stores, they’re available as fully rooted cuttings already, prepared from nurseries in different parts of the world.
I have an Althea bush from a “cutting” from my Grandmother’s house. The “mother” is over 100 years old. I planted my cutting in the ground. I thrived beautifully. After it was well over knee high with many healthy leaves, my landscape maintenance person accidently cut it down with a weed-eater. I’m so saddened because of it’s history. I have not done anything yet, just left it planted in the ground. Will it live; continue to grow again; be ok; or have I lost it?
Hi Gary, I’m transitioning the questions to “forum only” – time and time again I’ve had experts join in and give vastly better answers that I would myself.
I transferred your question there: How can I save a chopped-down althea shrub?. I’ll go answer there, hopefully even more people will have ideas, too.
My Athena produces generous blooms but does not mature into flowers. I have observed small something that appears to eat into the blooms. The “something” is not much bigger than a gnat and black in color. It covers the bloom which reaches distinguishable damage.
I live in Louisville, Ky. Is there a common parasite as described above? How do I treat the problem?
Hi Dwayne, there’s a chance it might be thrips. That’s a tiny insect that’s about gnat-sized. There’s more on thrips here and there’s also a page on how to wash thrips out.
Thanks for sending a photo over through email, Dwayne, I was able to zoom in a bit and it really looks like aphids instead of thrips. Thrips would be smaller, actually. So it’s black aphids that are sucking the sap from the flower buds, to the point that they can’t develop and unfurl properly. I wrote a new article for you: how to get rid of aphids on hibiscus (Althea is a type of hibiscus) and was able to use your picture.
There’s a lot on how to deal with aphids here, but as a first step, bring out the hose! Hose them off, either with a spray tip, or by capping the end of the hose with your thumb; they’ll fall to the ground and will have trouble getting back up. Do this every day for a week and you’ll see their numbers drop drastically. Every time you hose it down, from 75 to 90% of them will fall off; doing this for several days in a row is really effective.
You might also want to check for ants, and keep them from climbing up the tree. They shepherd aphids like sheepdogs, and if you block ants from climbing up the shrub, the aphids won’t be as colonizing.
Is althea tolerant of black walnuts?
Yes, it is tolerant of black walnut. You won’t have any problems planting althea under a black walnut tree!