How to successfully propagate Hibiscus
Large flowers, vivid colors: Hibiscus is not without reason extremely popular among amateur gardeners. Here, we’ll explain how you can successfully propagate hibiscus.
There are a number of different ways you can propagate Hibiscus. They need to be vegetatively propagated if you want to retain the typical characteristics of this variety, such as flower color. Grafting is the most reliable method, as cuttings are very bad at forming roots in domestic gardens. Growing from seed is mainly useful for breeding new varieties. This also lets you produce the seedling rootstock needed for grafting.
Chinese Hibiscus (Hibiscus rosa-sinensis), better known as Rose Mallow, is usually kept as houseplants in the US, but can also spend the summer in pots on the balcony or patio. It is best propagated from tip or stem cuttings. Cultivars of Swamp Rose Mallow (Hibiscus x moscheutos), which also thrive in our gardens and are relatively hardy, is propagated by seeds or by cuttings that are also true to the variety.
If you want to propagate your rose of Sharon from seeds, you need to harvest the dried up capsules in fall. Unfortunately, Hibiscus does not reliably produce seeds every year, only after long summers with high temperatures. Alternatively, you can buy the seeds in specialist stores. In any case, the seeds should be stored in a cool, dry place over winter. You can sow the hibiscus seeds under glass in March. You can also sow directly into the flower bed and in the garden once the last frosts have passed. It will take at least four to five years for Hibiscus propagated from seed to show its first flowers. Hardy Hibiscus is propagated in the same way, however it blooms much earlier.
Rose of Sharon often sows itself in the garden; the flower color and shape of the seedlings can differ from the mother plant later on. Also the wild cut seedlings are well suited as grafting substrates. But they can simply be transplanted and further cultivated in another part of the garden. For this purpose, carefully dig out the seedling in early spring with a hand shovel and reinsert it immediately at the desired location. If you want to use the seedling as your rootstock for grafting, you should grow the young Hibiscus in a pot for one year before grafting it the following spring.
Rose of Sharon is particularly bushy when it is propagated by grafting. Strong, potted Hibiscus syriacus seedlings - at least 0.27 inches in size - are used as the rootstock. Grafting takes place from early January to mid-February; the types used are the splice graft, whip-and-tongue graft and cleft graft. Try to propagate as close as possible to the root crown, otherwise lots of wild shoots can develop. Secure the grafting point with bast fiber and then seal with grafting wax. It is best to protect the grafted plants from frost by keeping them in a greenhouse or high tunnel. Move them into larger pots after they take root; they are best grown in a cold frame or high tunnel for the first year. They can be transplanted into the ground in the following spring. Important: young Rose of Sharon plants can be susceptible to frost in unfavorable locations. To be on the safe side, they should be covered with leaves and fir tree branches at the base in fall.
Ungrafted varieties of Hibiscus syriacus, such as the dark red-flowered ‘Rubi’, can also be propagated from root cuttings – however, they are generally slower growing than grafted plants. In fall, cut off fleshy portions of root - about as thick as your finger - and put them in moist peat. Root cuttings should be kept frost-free until they are used in December/January. Make sure that the roots do not completely dry out during this time. Cut the roots horizontally into pieces that are approximately four inches long and put them in the potting soil. Press the root cuttings about 0.5 to 0.75 inches into the soil. There is no need to water them, but you should keep the substrate evenly moist at all times. Put the propagation box in a cool, dry place. Move the young plants to a bright location as soon as the root cuttings produce new shoots. Fast-growing varieties can be planted out in the garden in late spring, all other varieties should first be grown in pots for one year.
Rose of Sharon can be propagated in winter by taking hardwood cuttings from the previous year’s shoots. It is best to take pencil-length cuttings in fall just after the leaves drop, and to put them in moist, slightly loamy humus-rich soil in a shaded, unheated greenhouse. The rooting percentage is not high, but around five to ten percent of the hardwood cuttings form roots by spring. The rooted hardwood cuttings can be planted out in flower beds once frosts have subsided.
In general, all Hibiscus varieties can be propagated from cuttings. However, for amateur gardeners, this method of propagation only proves promising for Rose Mallow (Hibiscus rosa-sinensis) and Swamp Rose Mallow (Hibiscus moscheutos). Rose Mallow cuttings are taken in spring, just after new growth emerges. If there are already flower buds on the cutting, you should remove them. June is the best time to propagate Swamp Rose Mallow from cuttings.
Softwood or semi-ripe tip or stem cuttings are used for propagation. Lightly scratch the base of the cutting (approximately four inches long) with the garden knife and put a little rooting powder (such as "Neudofix") onto it. Put three cuttings together in small multi-cell trays or biodegradable seedling pots. The cuttings are most likely to form roots with a soil temperature of at least 72 degrees Fahrenheit. If the timing is right and the substrate is warm enough, the first roots usually form within three weeks. It’s generally quicker for Swamp Rose Mallow.
Rose Mallow is not hardy and young plants need to be kept frost-free and not too cold when cultivated indoors or in a heated greenhouse. Swamp Rose Mallow can be planted in flower beds after overwintering indoors, but needs good winter protection.