Known for its large, pink to purple (sometimes white), trumpet-shaped flowers and long and late season blooming, Rose of Sharon is a hardy deciduous shrub from the Malvaceae or mallow family.
It is native to south-central and southeast China, but is also widely found in many other parts of the world, particularly in Asia.
In the United States, the plant can easily be grown in USDA hardiness zones 5 to 8.
Bearing the scientific name Hibiscus Syriacus, the plant is known with the following common names in different parts of the world:
- Syrian ketmia
- Shrub althea
- Rose mallow
- Korean rose (rose of Sharon is the national flower of South Korea)
Grown easily in full sun or partial shade in a range of soil types (well-drained soil is best), Rose of Sharon is an easy-to-grow and low-maintenance shrub. It is also fairly drought tolerant.
But, you have to be very careful when fertilizing.
While fertilizing helps improve overall health and encourages blooming, feeding at the wrong time or over-feeding can cause it serious damage.
Best Fertilizer for Rose of Sharon
A nutrient-rich organic matter is the best feed for new Korean rose plants.
After the first growing season, use a 10-10-10 fertilizer. To be on the safe side choose a slow-release one.
When and How to Fertilize Rose of Sharon Plant
Hibiscus Syriacus is not a heavy feeder.
It generally survives and continues to grow properly even in poor soils.
However, if your flowering shrub is exhibiting slow or stunted growth along with producing fewer or smaller blooms, it needs to be fertilized.
Fertilizing New Rose of Sharon Plants
To prevent growth issues, it is best to fertilize new althea plants with a nutrient-rich organic material at the time of planting.
While the organic matter is preferred, use a root stimulating fertilizer instead.
However, be careful to not use any fertilizer containing high amounts of nitrogen.
Higher levels of nitrogen in the soil will promote foliage growth, but at the expense of root development.
To feed the new Rose of Sharon shrubs, add fertilizer into the planting hole before setting in the plants.
Feeding Rose of Sharon Plants after the First Season
After the first season of growth, feed your rose of Sharon bush with a general-purpose fertilizer (10-10-10) once a year, in early spring, as soon as the new growth starts to emerge.
It’s possible to use any fertilizer meant for flowering plants, and it is better to use a slow-release one as it eliminates the chances of damage from over-fertilizing.
Many gardeners opt for the second dose of fertilizer in mid-summer to encourage better and more blooms in late summer. But, it is better to not risk over-feeding.
With the rose of Sharon hibiscus plants, under-fertilizing is better than over-fertilizing.
However, if you choose to feed your plant twice a year, opt for a balanced 10-10-10 or 10-20-10 fertilizer for spring feeding and use a light application.
For the mid-summer feeding, choose a low to no nitrogen fertilizer, such as 0-10-10
How Much Fertilizer to Use for a Hibiscus Syriacus Plant?
How much fertilizer or the amount of fertilizer a rose of Sharon plant needs depends on its size.
Measure the height of your shrub from the soil level to the tips and use one tablespoon of fertilizer for each foot.
How to Feed an Althea Shrub?
Water the plant well one day before fertilizing.
Fertilizing on dry soil can cause a chemical burn to roots.
If you are using a granular fertilizer, always water after applying it to help it get absorbed into the soil.
Add a layer of mulch around the base of the plant to help conserve moisture.
Read instructions on the fertilizer label for exact directions.
But, in general, be careful to only apply it at the drip line and not on the trunk or stems.
Signs of Over-fertilizing
Since it is easy to over-fertilize rose mallows, it is recommended to watch out for its signs and stop feeding the plant if you notice any of them.
Some of the most common signs of over-fertilization rose of Sharon shrubs display include:
- Yellowing or browning of foliage
- Withering of leaves
- The plant drying out
- Fewer and/or smaller flowers, typically with abundant foliage growth
Over-feeding also makes these plants from the hibiscus family more susceptible to aphid infestation.
Related: What Causes Yellow Leaves On Rose of Sharon Plants?
Many gardeners end up over-fertilizing hardy hibiscus shrubs in an attempt to encourage blooming.
But, this is not the right approach.
Follow the once or twice a year fertilizing schedule only.
To encourage Rose of Sharon blooms in your garden, prune the plant in late winter or early spring.
The ease-of growth, beautiful flower color and the plant’s ability to attract hummingbirds and butterflies make Rose of Sharon a wonderful addition in gardens.