In the garden, just as in almost all of life, fashions come and go. Some plants are popular for a time, and then fall out of favor – and then often come back again. That is the story of the Hardy Hibiscus, which is also known as Rose of Sharon, and in some places as Althea. This is one of the oldest plants grown in our gardens, and it would have been found in many European gardens in the 16th century. It was incredibly popular in America in the 19th century, and then it became ‘old-fashioned’. Gardening snobs labeled it as ‘too common’, and it wasn’t seen around very much at all. This century, though, it has seen a big revival, and new varieties are being introduced every year. No wonder there is renewed interest. For late blooming it is unsurpassed, flowering from midsummer right to the first hard-frost, which can often mean November in warm zones. It looks amazing blooming among the golden leaves of fall. It is also ridiculously easy to grow. Just find a suitable spot and watch it go. A little TLC from time to time makes a difference, but for low-maintenance gardening it can’t be beaten.
The blooms on this shrub are among the largest flowers of any garden shrub. Often 5 inches across, many varieties are as exotic and colorful as their close relative the tropical hibiscus. To add late blooms to your garden there really is nothing like it, and it will still be blooming when the hydrangeas are a memory. With its neat, rounded form it fits well into any garden, and it is versatile and adaptable to different locations and garden styles. It is naturally a bushy shrub, but with some staking and trimming it can be turned into a single stem or multi-stem small tree within two or three years, adding more possibilities for using it in your garden.
The secret to having the best garden beds is to have a long season of bloom – try to always have something flowering. That is easy in spring and early summer, when most shrubs flower. It gets hard as summer goes on, and even harder in fall. That is exactly when the hardy hibiscus is in bloom, so adding them to your beds will immediately extend your blooming season by months – a big win. They are a good size for the back of smaller beds, and for the middle area of larger ones.
Not every lawn is big enough for a shade tree, and on larger lawns there is room for shrubs as well as trees. Its long flowering season makes the Hardy Hibiscus a natural for that, and its bushy form is neat and rounded, looking perfect on the grass. Plant it where you pass it coming home, or where it can be seen from a window – it’s a great addition without adding work. It looks as good left as a full bush as it does pruned up into a small tree – the choice is yours.
With good resistance to dryness, and a moderate size, the Hardy Hibiscus is a terrific choice for big tubs and planter boxes. It can be pruned hard in spring to keep it no more than 4 feet tall, and tree-forms can have smaller plants surrounding them. These plants can stand on a terrace or patio, and of course if you have a large balcony or terrace on your apartment, you can grow them there too, without a garden at all. Plants in pots can be left outdoors all winter in zone 7 and warmer. In cooler zones it is best, if you can, to store them for the coldest months in an unheated shed or garage – they don’t need light when they have no leaves.
Hardy Hibiscus are deciduous shrubs, usually with many branches growing from their base, forming a dense, full, bushy plant. Most grow over 6 feet tall in the garden (smaller in pots) and some older varieties can reach 10 feet tall. They have a broad form, often vase-shaped, with a spread a couple of feet less than their height. The stems have a smooth, reddish-brown or grayish-brown bark, which becomes rougher on older stems. The leaves are typically 3 or 4 inches long, and they are divided into three distinct lobes at the end. They are smooth and glossy, and the edges have irregular serrations around them. They are attractive, and their rich green color is reliable even in hot weather. In late fall they turn golden yellow, and then fall to the ground for the winter.
As new stems grow in spring, clusters of flower buds develop at the base of the leaves. These open one after another once flowering begins. Each flower lasts between 1 and 4 days, but it is quickly replaced by more, so the bush always has a profusion of blooms. In hot areas flowering usually starts in June, and in July elsewhere. It often continues until the first hard frost, which can be November in warmer zones.
The classic bloom of the Hardy Hibiscus is a wide, flaring trumpet, with 5 to 7 broad petals. It sits in a green cup at the end of the flower stalk. In the center is a long column that contains the stamens producing pollen, and the parts that develop into the seed pod. The colors vary a lot, from white to pink and red, as well as mauves, lilacs and purples. Often the center of the flower has a dark-red blotch in it, which can spread up the veins of the petals, and darken the color of the lower parts of the flower, adding interesting shading. In the 19th century the first double-flower forms appeared. In these the central column is transformed into many slender petals, and these are often twisted and fluted. They form a large central group, turning the flower into a pom-pom, often of great beauty.
This fast-growing shrub really is a true ‘low-maintenance’ plant. Left untrimmed it may grow large, but it will still bloom prolifically. With a little attention – some pruning, fertilizer and the occasional watering – it will thrive and really look great all the time.
Hardy Hibiscus are usually reliably hardy from zone 6 to zone 9, thriving in warmer zones. They will grow in zone 5, planted in a sunny, sheltered spot. They may have some winter damage to the stems, but since this plant flowers on new stems it will still bloom well once new growth begins, although the plant will be smaller than its listed size.
You can definitely place Hardy Hibiscus among the sun-lovers in your garden. They thrive in full sun in all climates, and really need it in cooler areas. In warm zones they will still perform well with a few hours of afternoon shade, but they will always do best with all the sun they can get.
Tough and reliable, Hardy Hibiscus grow in almost any kind of soil. This makes them good choices in urban gardens, where the soil can be poor following construction. They will grow in dry, sandy soils, and clays too. It is also true that they do best in richer soils, with a steady supply of moisture – soils that can keep up with their rapid growth. What they don’t like is ‘wet feet’, so never plant in low-lying parts of your garden, or in areas that are regularly wet. This is especially important in zones 5 and 6, where it can cause plants to die during winter. Adding plenty of organic materials like compost will make sandy soils richer and make clay soils drain better – a win-win for these plants.
Very little attention is needed to grow these plants successfully. Water once a week when they are newly-planted Established plants will tolerate long periods of dryness, but they appreciate a deep soaking from time to time – it keeps them vigorous and growing well.
Pests and diseases are rare, especially in well-drained soil and full sun, and deer usually won’t eat them. Some leaf pests like aphids, white fly and mites are possible, but these can usually be controlled with soap sprays or neem oil. In some parts of Texas, cotton root rot (Phymatotrichum) is a serious problem, and Hardy Hibiscus can suffer when planted in soil carrying this fungus. Ask your local USDA field office, and if it is common in your area, grow your plants in a large tub raised a few inches off the ground. This is a local problem, and in almost all of the country you will be able to grow Hardy Hibiscus with ease.
Hardy Hibiscus are naturally neat in form, with bushy growth, so you can almost forget about pruning. It is best, though, especially for young plants, to prune once a year – in late winter or early spring. Since flowers develop on new shoots, we want plenty of those to grow each year. This is stimulated by cutting back the stems that grew the previous year. How much depends on where they are growing. In tubs you can cut hard, leaving just 2 or 3 buds on those stems. Your plants will be smaller, with very large blooms. Out in the garden leave about 12 inches of stem, cutting above an outward facing bud. Older bushes can have up to one-third of the older branches removed close to the ground, but you can also just leave your plants, with minimal trimming, if you don’t need to keep them smaller. It is also possible to prune lower branches away, developing a taller, tree-like plant.
This plant is a relative of tropical hibiscus, and also of cotton and okra. Called Hibiscus syriacus, it originally grew wild in China and India, and it was grown in gardens in Asia for many centuries. It is the National Flower of Korea, first mentioned there 1,400 years ago, and today it is used as a logo on many government publications.
It came to Europe from Syria, where it was grown in gardens. It is likely that the plant was brought to Syria along the Silk Route, riding on camels alongside spices and fabrics. We find it mentioned in John Gerard’s massive, Herball, or Generall Historie of Plantes, a famous English gardening book for 1597, as ‘Syrian Ketmia’, so we know it was in Europe by then. It remained popular as ‘Tree Mallow’ and seeds were brought to America by the first settlers. Thomas Jefferson describes sowing seeds at Shadwell in 1767 and planting it at Monticello in 1794. All through the 19th century, especially in the South, it was hugely popular. By the 1850s there were many varieties, both single and double, often brought over from Europe, and more nurseries in the South listed ‘Althea’ than roses.
It remained popular well into the 20th century, but then lost favor and was replaced by all the new plants that appeared during that time. This century there has been a huge revival of interest, with new varieties appearing. The interest in ‘heirloom’ plants and the desire for tough, reliable plants that will grow well for today’s busy gardeners, means plants like the Hardy Hibiscus have a bright future.
The original form of this plant, with its lilac single blooms and dark center, is still seen, but it has been mostly replaced with selected forms in a wide range of colors, and with flowers that have single, semi-double and double blooms.
Most double blooms can’t produce seeds, since their sexual parts have been turned into petals. Older single varieties make seeds and this diverts energy from blooming to seed-production, shortening the blooming season. Since we want a long season, and no pesky seedlings sprouting around, for single varieties it is best to choose ones that don’t make seeds. The best of these were created by Dr. Donald Egolf, a breeder with the US Department of Agriculture. He took plants of an old white single developed around 1916, called ‘William R. Smith’, and treated them with a chemical called colchicine to increase the number of chromosomes. He then did some complex crosses that included rare Asian varieties. The result was seedlings with odd numbers of chromosomes, called triploids, that can’t make seeds. The varieties we have from this work are definitely the best single flowered forms for the garden, with a compact form growing only 6 to 8 feet tall.
‘Diana’ –the enormous pure-white flowers never stop coming.
‘Helene’ –white flowers with a blood-red heart
‘Minerva’ – the ruffled edges to the blooms highlight the mauve-pink coloring
‘Aphrodite’ – a beautiful rich pink
There are just two of these, but for big blooms they can’t be beaten. With the largest blooms of any variety, on compact bushes, they are perfect for planters. They were created by Dr. Sam McFadden, a professional plant breeder who turned to hardy hibiscus as a hobby when he retired.
Blue Angel (‘Greba’) has true sky-blue flowers
White Angel (‘Greba’) has large, very frilly blossoms and is a unique hybrid between hardy hibiscus and tropical hibiscus.
The Lil’ Kim® Hardy Hibiscus are perfect for smaller gardens, growing only 3 or 4 feet tall. The flowers are also smaller, with a large, radiating red heart. There are three colors in the range – white, violet, and red.
These are all larger shrubs, up to 10 feet tall in warm zones, and they are perfect for planting in older gardens to give the right feel.
Double Red – ‘Amplissimus’. This French variety was certainly in existence before 1861, and it has big red-purple pom-pom flowers in profusion.
Double Purple – ‘Ardens’. The purple-pink flowers have a center of twirling extra petals, with dark-red bases. This is also probably French, first mentioned in 1873.
Double White – ‘Jeanne D’Arc’. Magnificent blooms like white peonies have made this plant popular since the 19th century.
Double Pink – ‘Lady Stanley’. Named after the wife of the man who founded hockey’s Stanley Cup, this English variety was first listed in 1875. It has white petals, with a partly-hidden red heart that spread pink across them, making a beautiful soft coloring.
Smoothie™ Hardy Hibiscus – Don Shadow, a breeder from Tennessee, and the Greenleaf Nursery Company of Oklahoma got together this century to update double blooming forms. The results are compact, bushy plants in a range of colors, all of them beautiful. They are bright, bold, and delicious.
With so many forms to choose from, you could build a whole garden with Hardy Hibiscus. From small to large, and in planters or the garden, they really are the way to bring color and interest to the second-half of the gardening season.