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Perennial Hibiscus 101

Perennial Hibiscus

(📸 Michel VIARD from Getty Images)

Most of us become fixated with tropical hibiscus (Hibiscus rosa-sinensis) after visiting exotic locales such as Hawaii or Mexico and come late summer many gardeners typically shop for Rose of Sharon (Hibiscus syriacus) at the garden centre, but surprisingly very few people seem to have any experience with perennial hibiscus until they stumble onto their massive blooms (which can range anywhere from 6-12” across) and ask "What is that?"

Most perennial hibiscus are complex hybrids bred from several species including H. moscheutos (Swamp Rose Mallow), H. laevis (Halberd-Leaf Mallow) and H. coccineus (Scarlet Hibiscus), all of which are native to temperate North America. In the wild they are generally found in wetlands or stream sides, and they are all herbaceous perennials that die back to the ground each winter and regrow new stems the following spring.

Hibiscus 'Summerific Holy Grail' - Proven Winnners

(📸 Proven Winners | Hibiscus 'Summerific Holy Grail')

In my opinion there really should be a lot more of these specimen perennials planted in local gardens and with that in mind, here are the answers to the most common perennial hibiscus questions that I receive.

Are perennial hibiscus hardy?

Hibiscus 'Summerific Spinderella' - Proven Winners

In a word, yes, as the species range from USDA zone 4-6 and most of the hybrids are rated at USDA zone 4, which is hardier than the shrubby Rose of Sharon or Hibiscus syriacus.

How much sun do perennial hibiscus need?

These are not shade-loving perennials, preferring part to full sun exposures, with 6 hours being considered a minimum. If you can choose a site where the early spring sun warms the soil, they will break dormancy sooner and provide a longer flower display.

When do perennial hibiscus flower?

Hibiscus 'Carousel Giant Red' - Proven Winners

(Hibiscus 'Carousel Giant Red')

The species generally bloom from July to September, with many of the hybrids lasting well into October, depending on the weather.

How much water do perennial hibiscus need?

Hibiscus 'French Vanilla' - Proven Winners

(Hibiscus 'French Vanilla')

Perennial hibiscuses are best located in moist soils, but if that’s not possible, then they will need regular watering (1-2” per week) and should never be allowed to dry out when growing or in bloom.

How tall do perennial hibiscus grow?

Hibiscus 'Dark Mystery' - Proven Winners
(Hibiscus 'Dark Mystery')
These are specimen perennials with massive flowers that show well at a distance. They can grow anywhere from 3-7’ tall on average and form clumps 3-4’ wide, so give them room to mature.

What flower colours are available?

Hibiscus 'Strawberry Swirl' - Proven Winners

(Hibiscus 'Strawberry Swirl')

Red, pink, white and creamy-yellow are typical bloom colours, many with a contrasting eye or veining. These can be further enhanced by variegated or rich burgundy-black foliage available on some cultivars.

Do you have to deadhead the spent blooms?

Deadheading is not necessary, but it will improve the overall appearance and extend the flowering season.

Is pruning necessary?

Hibiscus 'Starry Starry Night' - Proven Winners

(Hibiscus 'Starry Starry Night')

Yes, but only once a year. Leave the old stems intact for winter and cut these down to 4-6” using loppers or a small handsaw in spring, when the new shoots emerge from the soil.

When do you fertilize and with what?

Fertilize in spring once the new shoots emerge using a slow release such as 14-14-14. Be warned that this is one of the last perennials to emerge in spring, with many gardeners often prematurely discarding what they thought was a dead plant.

Do perennial hibiscus require winter protection?

Hibiscus 'Summerific Berry Awesome' - Proven Winners

Despite being so cold hardy, young plants should have their crown mulched heavily for their first winter and even established clumps will benefit from this.

Are perennial hibiscus good pollinator plants?

Perennial hibiscuses are much sought after by both bees and hummingbirds for their delicious nectar.

Well, there you have it. Easy answers for an easy-to-grow perennial that is just waiting to be planted along your bare fence line or at the back of your soon-to-be spectacular mixed border. Regardless of where you plant them, there’s no way your neighbors won’t be jealous of those massive late summer to autumn blooms.

All images Copyright 2024 MK Lascelle, except those already credited.

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