How to prune Hibiscus
There’s no obligation to prune Hibiscus, but the ornamental shrub produces an abundance of blossoms in summer if the previous year’s flowering shoots are hard pruned in late winter.
If you prune your Hibiscus correctly, the ornamental shrub rewards you with a luxuriant bloom in summer. The woody plant takes well to cutting and can even tolerate being cut back to the old wood – even if it takes the slow-growing shrub a bit longer to become nice and compact again. The type of pruning depends on the age of the Hibiscus and the growth form being trained. Here are some instructions and practical tips.
Note: Shrub Althea or Rose of Sharon (Hibiscus syriacus) is the only flowering shrub of the genus Hibiscus that is hardy in these parts. You should use a layer of mulch to protect young plants from severe frost in the first winter after planting, but there’s no need to worry about frost damaging larger plants. You should nevertheless treat Hibiscus to a warm, sunny spot with a favorable microclimate so that it grows well and flowers freely. The shrub needs to be protected against cold easterly winds in particular.
Hibiscus should be pruned on a regular basis to keep it beautiful, healthy and free flowering. Formative pruning begins immediately after planting, subsequent pruning helps with maintaining the crown, thinning and rejuvenation. Most pruning takes place in late winter or spring.
Formative pruning is carried out on young Hibiscus plants. During planting, remove any weak or damaged branches. Use shears to shorten the remaining shoots – it’s usually no more than two or three for young plants – by at least half to stimulate branching. Young plants should also be heavily pruned in subsequent years to encourage branching at the base.
Removing branches at the base makes the basic structure somewhat airier and allows young, energetic shoots to grow back from below. For this type of cutting, it’s best to use pruning shears with a small opening angle, because they make it easy to get to the inner parts of the shrub and you can position them directly at the branch joint. Inward growing branches should be completely cut off to let more light into the crown.
For competing shoots, place the shears on the v-shaped crotch and remove one of the two branches. This prevents them from hindering each other’s growth. It may seem like the front branch has grown outwards nicely, but unfortunately it has dried up and needs to be removed. Before doing so, you should use the shears to scratch off a little bark to make sure that there is no living tissue underneath.
Cut back long, thin flower branches leaving just a few buds. For heavily branched ends with lots of short growth from the current season, it is best to cut back to the second year wood. These develop when the shrub has not been pruned for several years. It’s important that there is a viable young branch below the cutting point or, like here, an outward facing eye. When pruning, you should try to maintain the natural crown shape of your Hibiscus by shortening the branches in the center less than those in the outer part of the crown.
New buds continually open on Hibiscus until the end of September. You should make some light thinning cuts the following year so that the crown doesn’t become too dense with new growth and it remains free flowering.
If the crown of your Hibiscus has developed satisfactorily, in future you only need to fully remove weak and dried up shoots. Cut back flowering stems from the previous year to leave just a few buds. However, since the ornamental shrub gets denser and denser over time, it needs to be thinned out now and again. This is achieved by completely removing part of the previous year’s flowering shoots. Remove one of the two shoots from the previous year on several crotches.
For established standards, you can either leave the crown to grow freely in subsequent years or treat it like a pollarded willow by, each year in February, removing all of the previous year’s shoots from the sturdy framework of branches, except for a few buds.
If the ornamental shrub is only growing on one side or is struggling to bloom after several years without pruning, rejuvenation pruning can put things right. To do this, simply cut all of the branches back to various heights between 12 and 20 inches above the ground. The Hibiscus will show new growth in many places in subsequent months. This new growth needs to be significantly thinned out in summer, leaving behind only the necessary leaders and branches from the old main stem. You should not expect the plant to flower in the first year after a hard rejuvenation prune, as the shrub’s first task is to make up for the substantial loss and it therefore limits itself to the vegetative growth phase. If the summer after the rejuvenation prune is very dry, you should water your Hibiscus regularly – otherwise, the shoots will remain very short that year.
You’ll need plenty of patience if you want to train your Hibiscus to grow as a standard, because it takes several years for it to fully develop this growth habit. During pruning, remove all shoots and stems, leaving only the strongest main stem uncut. In early February of subsequent years, cut back to the branch collar all shoots that emerge on the sides of the main stem, and otherwise leave the stem to grow undisturbed until it is slightly higher than the point where you would like the crown to begin. Cut off the top in early spring to stimulate sprouting of the buds underneath. Use a thin bamboo stick to vertically guide the central leader to grow up from the top of the new side branches. The remaining three to four side shoots form the main branches of the crown – shorten them by around a half to allow them to branch well.