Don’t let the name put you off. Hibiscus syriacus is not from Syria or any other part of the middle east, but is actually from the mountains of China and is quite suited to our cooler UK climate being ‘fully hardy’. In my mind, if I were to some up the word ‘tropical’ with one flower, it would be this one.
You’d be amazed on how surprised people are to see these unusual and highly attractive deciduous flowering shrubs in an English garden. Hardy hibiscuses can be allowed to grow into bushes, or (if you have more time on your hands) into standards. They will happily put out their large blooms from late summer until Autumn.
Caring for your hardy hibiscus
They prefer a well drained, but fertile soil. Plant in full sun and add a good organic mixture of compost or well-rotted manure. As with most plants and shrubs, it’s a good idea to gently tease a few roots out from the root ball. This will encourage them to spread throughout the soil to seek out moisture and nutrients. I like to add a sprinkling of mitochondrial fungus (Root Grow) into the hole before planting to encourage root growth. Water until established and throughout dry periods. I would also recommend applying a layer of leaves, several inches thick in winter and remove them again as the weather warms.
Hardy hibiscuses flower on this year’s new growth, so you don’t need to worry about losing your year’s blooms after a trim. You can be pretty mean to them, hard pruning in late spring in a manner very similar to pruning roses. Pruning will encourage more shoots to form and as a result, more flowers. Remove spent hibiscus flowers to encourage more growth. Keep your shrub healthy by ensuring that you remove any weak or dead branches.
To get the most out of your hardy hibiscus, feed with a good organic rose fertiliser annually during spring. I also like to dress my plants with a layer an inch or two thick of mulch to retain moisture. This will also frost protect the roots and keep the soil cool during hot weather.
Aphids and red spider mites can be an issue, but you can treat them both with a good organic insecticide. Hibiscuses are also a little prone to powdery mildew.
Hardy hibiscuses are reasonably easy to propagate. If you want to make more plants, you could either try layering, which many people have reported good results from. You could also try 5 inch soft or semi-hardwood cuttings. Dip them in hormone rooting powder and push into a 50/50 mix of grit and cutting compost. Place cuttings on a warm bright windowsill or in a propagator. Either method will take 4-6 weeks for roots to develop. I have also heard of gardeners growing them from seed with some success.
Be patient with your hardy hibiscus during spring. They can be a little slow to come into leaf. I’m sure that many a perfectly healthy plant has ended upon the compost heap due to impatience.