Hibiscus Plant Care Findings From Our Interview With The International Hibiscus Society

SHRUBS > HIBISCUS

Hibiscus is a large genus of flowering plants: there are hardy hibiscus types that can thrive outside in many UK gardens, and tropical types can be grown as houseplants indoors.

In this article, we will focus on two of the most common Hibiscus in cultivation – the hardy Hibiscus syriacus, also known as Rose of Sharon, Rose Mallow or Tree Hollyhock, and the popular houseplant Hibiscus rosa-sinensis.

We interviewed Darren Eminian to help produce this guide – Darren is the President of the Southern California Hibiscus Society and the International Hibiscus Society.

“My passion for hibiscus comes from the incredible and second-to-none combination of multiple colours on large blooms that few, if any, other species of plants can produce” says Darren.

Explore his tips for making the most of your plants in the guide below.

Overview

Botanical Name	Hibiscus
Common Name(s)	Rose of Sharon, Rose Mallow, Tree Hollyhock
Plant Type	Shrub / Tree
Native Area	Temperate subtropical and tropical regions
Hardiness Rating	Varies
Foliage	Deciduous
Flowers	Trumpet-shaped with numerous hues
When To Plant	April-May (for hardy varieties grown outdoors)
When To Prune	June

There are several hundred different species of hibiscus, which are included within this diverse genus of flowering plants in the Malvaceae, or mallow, plant family. ¹The Editors of Encyclopaedia Britannica. (1998d, July 20). Hibiscus | Description, Species, & Uses. Encyclopedia Britannica. Retrieved March 17, 2023, from https://www.britannica.com/plant/hibiscus

Hibiscus can be found around the globe, in temperate, subtropical and tropical climes. ²Hibiscus History. (n.d.). Hidden Valley Hibiscus. Retrieved March 17, 2023, from https://www.hiddenvalleyhibiscus.com/history/earlyhistory.htm

The genus includes trees, shrubs and herbaceous plants – both perennial and annual.

Of all the plants within this genus, two are most widely cultivated as ornamental plants: H. syriacus (grown outdoors in the UK) and H. rosa-sinensis, which is grown as a houseplant in temperate areas.

The former is by far the easier option.

When planted in an appropriate spot and cared for correctly, H. syriacus can flower extremely well from late summer into early autumn.

H. rosa-sinensis, also known as tropical hibiscus, is usually grown indoors, though it may succeed in a warm greenhouse as long as this remains frost-free over the coldest months.

They can be rather difficult to grow successfully and are not necessarily to be recommended for novice houseplant gardeners, but when successfully grown, can bloom beautifully from May right through to October.

Recommended Varieties

Some varieties of H. syriacus to grow in the UK include:

• ‘Ardens’
• ‘Chiffon’ Series
• ‘Duc de Braband’
• ‘Marina’
• ‘Monstrosus’
• ‘Oiseau Bleu’
• ‘Red Heart’
• ‘Sugar Tip’
• ‘Totus Albus’
• ‘Woodbridge’

Some H. rosa-sinensis cultivars include:

• ‘Columbine’
• ‘Holly’s Pride’
• ‘Karmen Keene’
• ‘Me Oh My Oh’
• ‘Peaches & Cream’
• ‘Pink Frost’
• ‘Sprinkle Rain’
• ‘Tarantella’
• ‘Velvetine’
• ‘White Swan’

“With H. rosa-sinensis, I prefer to grow most varieties from the ‘Hidden Valley’ hybrid collection, because they are the only hybridizers dedicated to creating new hybrids that have strong and vigorous bushes with large blooms that bloom often,” Darren explains.

Growing Hibiscus

Your first decision, of course, will be whether you wish to grow hibiscus in your garden or indoors.

In order to make this decision, you will have to determine whether you can create the right conditions for either hardy or tropical hibiscus where you live.

The plant care requirements outlined below will help you understand what is possible and the conditions each of these two common hibiscus types require.

Planting

“Every growing location has it’s own unique parameters so it takes time to see what tweaks need to be made,” says Darren.

“The base need for hibiscus is a soil mix that is light and full of air all the time even when wet. Hibiscus will struggle to survive in clayey soils in the long term.”

Dig a hole large enough to accommodate your new plant in a suitable location and place the new shrub in the hole you have excavated, or place your hibiscus in a container filled with a suitable growing medium.

Mulch with an organic matter around your new plant to retain moisture over the summer months and to provide slow-release fertility.

When To Plant

When growing hardy hibiscus outdoors, you will usually purchase and plant your new shrub in late spring.

Tropical hibiscus can be purchased and potted up at any time, though again, repotting in spring is generally best.

Where To Plant

H. syriacus should be placed in a sunny spot which is as warm and sheltered as possible.

This plant will be easier to grow in the south, or in very sheltered city gardens where your plants are less likely to be impacted by frosts.

You can also plant in a container so you can bring your plant undercover in the coldest part of the year.

In a suitable spot, sheltered from cold winds, this plant should make it through the UK winter unscathed, though some protection may be necessary for more northern areas.

H. rosa-sinensis is grown indoors, in a location with bright but not direct sunlight.

Growing these plants in a frost-free conservatory or a bright bathroom can be ideal.

Container Growing

Both types of hibiscus under discussion in this article work well in containers.

Choose a container which can drain relatively freely, and fill with a medium which meets the soil requirements and other environmental needs discussed below.

Ongoing Hibiscus Care

H. syriacus placed in a suitable location should usually be a relatively easy and trouble-free plant, which should require little care and attention, especially once well-established.

H. rosa-sinensis can be more challenging to grow, but following the care guide below should help you to grow this plant as a houseplant in your home.

Darren argues: “The Golden Rule of growing hibiscus is ‘What you see today was caused by events 2-3 weeks ago’.

“So you have to keep track of inputs like weather, temperature, water or rain, what you fed them and so on…so you can get to the cause of a problem.

“Being very patient and a keen observer is key so you can track inputs and start to figure out what works and what doesn’t.

“Understand that you might lose quite a few plants as you come down the learning curve which can take 2-3 years minimum.”

Soil Requirements

H. syriacus requires a moist yet free-draining soil or growing medium which is ideally neutral or slightly alkaline.

If growing in a container, a loam-based, peat-free compost is ideal.

H. rosa-sinensis also requires a moist yet free-draining medium, and it is essential to choose containers which allow water to drain away relatively freely for both types.

Watering

H. syriacus should be watered regularly during dry spells during the growing season when rainfall is in short supply.

However, these plants are relatively tolerant of dry conditions once established.

The “number one problem [when growing hibiscus] is too much water or not enough air in the soil” according to Darren.

“Hibiscus roots are tender and vulnerable to root rot.”

As such they do not do well with sprinklered water: “they do better with a drip system and if you can install a fertiliser injector that is a great way to get them to thrive.”

Remember that plants grown in containers will usually need to be watered more frequently.

Water indoor-grown H. rosa-sinensis regularly from spring through to autumn, but always let the top few centimetres of the potting mix dry out before watering once more.

Remember to cut down on watering during the dormant period, watering only when the top few centimetres of the growing medium are dry.

Temperature & Humidity

H. syriacus can cope with the UK winter but will need a warm and sheltered spot to flower well, which is why they are easier to grow in the south.

A spot in a sunny courtyard garden or against a south-facing wall might be ideal to maintain the summer and early autumn temperatures required for a good flowering display.

H. rosa-sinensis cannot cope with temperatures below 7-10°C.

They must be kept in a location where it does not drop below these minimum temperatures.

Tropical hibiscus also requires high humidity.

They can drop their buds if the humidity drops too low so it is important to mist regularly or to move to a bathroom or another more humid location.

Feeding

“For feeding, hibiscus needs lots of potassium, which is key for root development and health,” Darren shares.

“As their roots are tender, this goes a long way in helping them become established and strong. They don’t need much in the way of nitrogen, phosphorus, or other common plant nutrients.”

With this in mind, H. syriacus should be fed with a high-potassium organic liquid feed each year in the spring.

It can also be beneficial to add a thick organic mulch around the plants in autumn, for slow-release fertility as well as for a range of other reasons.

Indoor-grown hibiscus should be fed once every couple of weeks from spring to the beginning of autumn with a high-potassium organic liquid plant feed.

Overwintering

As Darren explains, “H. rosa-sinensis is a tropical plant, so it isn’t genetically bred for seasons and cold weather events.”

This does not, however, mean that you can’t or shouldn’t grow your hibiscus outside here in the UK.

A hard frost in autumn may well cause your H. syriacus to die back, but this is not something to worry about.

This is a deciduous plant and the plant should regrow from the base the following spring.

You might think that your plant is not regrowing, but you should note that the plants develop slowly in spring and new growth can be slow to appear.

Wait until June before you worry about the lack of new growth.

“Established woody H. syriacus plants are normally fully hardy in most parts of the UK and resume growth in mid to late spring,” shares Master Horticulturist Roy Nicol.

In colder and more northern areas, it is best to add a thick mulch of carbon-rich organic matter around the base of the plants in autumn to make sure that they overwinter successfully.

In particularly cold areas, you might wish to take container-grown plants into a greenhouse or conservatory – though this is not usually required.

Make sure that you have cut back on watering H. rosa-sinensis indoors during the winter months during its period of dormancy.

Pruning & Training

After around three years, once a H. syriacus is established, or after it reaches a height of around 1.5m, it is a good idea to start pruning the plant annually to keep it in shape.

While not always strictly necessary, pruning can help prevent the outer branches from falling outwards with the weight of their leaves.

H. rosa-sinensis should be pruned each year in early spring.

Prune back long shoots to 5-7cm from their base, shorten the previous year’s growth to create a main framework of branches, and remove thin or straggly non-flowering stems.

“As both types of Hibiscus flower on the new growth produced in the current year, timing is important to ensure good flowering, so pruning should be carried out just before growth starts in early spring,” advises Roy.

“Delayed and reduced flowering will be produced if pruned later than this.”

Common Problems

“As you problem-solve issues with your hibiscus it might take most of one growing season to see if what action you took worked or not” says Darren.

“So the learning curve for becoming an effective hibiscus grower can take 2-3 years minimum as you figure out the correct inputs needed and actions to take when problems arise.”

Issues with H. rosa-sinensis are usually environmental, but look out for spider mites, which can become a problem – especially where humidity is too low. ³Hibiscus. (n.d.). University of Florida, Institute of Food and Agricultural Sciences. Retrieved March 17, 2023, from https://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/hibiscus.html

Root Rot

Many times when Hibiscus are struggling with root rot their leaves will become pale and veiny – which to many gardeners is an indication that the plant is lacking nutrients like iron, magnesium or nitrogen.

“So they water in supplements which is the exact opposite of what the roots need which is more air in the soil.

“The additional water can prove to be fatal.

“Instead back off on watering for a couple weeks and check the soil with a water meter to see how wet it is deep down where the roots are” says Darren.

“Changing the soil mix many times is the difference maker but what you use depends on the climate and resources available to you so it differs with each region.”

Pests

Pests are another big challenge in the more tropical, humid areas of the world, but not particularly in UK growing conditions.

Sometimes even with ideal climate conditions, pests can prove to be a never-ending problem greatly reducing the performance of a hibiscus.

Darren says: “unfortunately we have tested many of the organic remedies and have found very little success with them, so proper and careful treatment with specific insecticides/miticides is key”.

Of course we would always argue that this should be a last resort where organic solutions are not fruitful.

Propagation

H. syriacus can be propagated by means of seed, softwood cuttings or layering.

Taking softwood cuttings in spring is usually the easiest option.

While it can be somewhat more challenging to root them successfully, H. rosa-sinensis can also be propagated most easily by means of softwood cuttings.

However, this is very hard with many hybrid cultivars and may not be very easy for most home growers.

If you have any specific questions, Darren recommends that you reach out to hibiscus specialists, like those in the International Hibiscus Society, for relevant tips and tricks.

References

• 1
  The Editors of Encyclopaedia Britannica. (1998d, July 20). Hibiscus | Description, Species, & Uses. Encyclopedia Britannica. Retrieved March 17, 2023, from https://www.britannica.com/plant/hibiscus
• 2
  Hibiscus History. (n.d.). Hidden Valley Hibiscus. Retrieved March 17, 2023, from https://www.hiddenvalleyhibiscus.com/history/earlyhistory.htm
• 3
  Hibiscus. (n.d.). University of Florida, Institute of Food and Agricultural Sciences. Retrieved March 17, 2023, from https://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/hibiscus.html