Posted by Brent Wilson on 11/10/2016 to Fertilizing & Watering Tips
When planted right and in the right spot, Hibiscus syriacus, commonly called Rose of Sharon or Althea, are exceptionally easy to grow.
Here's a breakdown of what you need to know for how to plant and care for Rose of Sharon Hibiscus...
Rose of Sharon will grow in a wide range of soils, including clay soils, preferring a moist but well-drained soil. As with so many other types of ornamental plants, constantly wet soils can cause root rot and other harmful plant diseases.
How To Test Soil Drainage
If you are uncertain about soil drainage in the area you intend to plant your Rose of Sharon, it's well worth taking the time to test the drainage before planting.
To test soil drainage, dig a hole 12" wide by 12" deep in the planting area. Fill the hole with water and let it drain. Then, after it drains, fill it with water again, but this time clock how long it takes to drain. In well-drained soil the water level will go down at a rate of about 1 inch an hour. A faster rate, such as in loose, sandy soil, may signal potentially dry site conditions. A slower rate indicates poor draining soil and is a caution you need to improve drainage, plant in a raised mound or bed, or look for plants that are more tolerant of wet or boggy soil conditions.
Rose of Sharon thrive in a wide range of soil pH from around 5.5 to 7.5 on the pH scale. Most average garden soils fall between a pH range of 6.0 to 7.0.
Testing Soil pH
Soil pH is a measurement of the alkalinity or acidity of soil and is measured on a scale of 1-14, with 7 as the neutral mark. Any measurement below 7 indicates acid soil conditions, and anything above 7 indicates alkaline.
If you're unsure about the pH of your soil, and whether or not it's suitable for growing Rose of Sharon, it's a good idea to test the soil pH in the planting area. You can quickly test soil pH with an inexpensive soil pH tester probe. To raise the pH (make more alkaline) you can add pelletized limestone to the soil. To lower the pH (make more acid) you can apply Soil Sulfur, Aluminum Sulfate, or Chelated Iron. Adding organic compost to the soil or using compost as mulch can also help to increase acidity and maintain acid soil conditions.
Learn More: What is Soil pH and How To Adjust It?
Rose of Sharon will grow well in full sun or part shade. For best flowering and overall performance, we suggest a minimum of 6 hours direct sunlight.
How To Plant A Rose of Sharon Hibiscus
Scroll down for container planting instructions and care tips
Start by digging your planting hole at least two to three times as wide and as deep or not much deeper than the root ball of your Rose of Sharon. The wider the hole the better. Place native soil removed from planting hole around the perimeter of the hole, in a wheel barrow, or on a tarp.
Depending on the type, fertility and porosity of the soil in the planting area, it might be beneficial to amend the native soil. When planting in heavy clay or poor soil it is beneficial to thoroughly mix in a good soil conditioner, planting mix, or other organic matter at a 50/50 ratio with the soil removed from the planting hole. When planting in very sandy, quick-draining soil top soil, organic compost, or peat moss can be added to help retain moisture. When planting in fertile, moist but well-drained soil there is no need to amend soil.
To remove your Rose of Sharon from the container it was growing in first squeeze the sides of the container to loosen root ball. Then grasp the base of the plant and very gently try to lift and remove the root ball from its container. If the root ball is stuck in the container it's best to use snips to cut away the container. After having removed the plant from the container, loosen some feeder roots around the surface of the root ball. If root bound, you can spray the sides and bottom of the root ball with a stream of water from a garden hose. This will help to wash away some soil from the exterior of the root ball making it easier to loosen roots.
Set your Rose of Sharon in the planting hole so that the top edge of the root ball is at or slightly above ground level to allow for settling. If necessary, add some backfill soil mixture to the bottom of the hole to achieve proper planting height.
Note: If the soil is poorly drained (constantly soggy or wet) improve soil drainage in the planting area or select a different plant species tolerant of wet soils.
After setting your Rose of Sharon in the planting hole, use one hand to hold the plant straight and your other hand to begin back-filling your soil mixture around the root ball, tamping as you go to remove air pockets. When you have filled the hole to the halfway point you can soak the soil. Then continue back-filling to the top edge of the root ball. To avoid suffocating your plant, do not put any soil on top of the root ball.
Note: If you are planting your Rose of Sharon with the top of the root ball above ground taper your soil mixture from the top edge of the root ball to ground level so that essentially your are planting in a raised mound. Roots should not be exposed above ground.
Step 6 (Optional)
When planting your Rose of Sharon far away from a water source, you can use remaining soil mixture to build a water retaining berm (catch basin / doughnut) around the outside perimeter of the planting hole, as shown in the diagram above. This basin will help to collect water from rainfall and irrigation often reducing watering frequency. The berm can be removed after a growing season or when the plant has established itself.
Next, deeply water the planting area, including the root ball, to a depth equal to the height of the root ball. For an extra boost, you can water your newly planted Rose of Sharon with a solution of Root Stimulator, which stimulates early root formation and stronger root development. Root Stimulator reduces plant shock and promotes greener, more vigorous plants.
To conserve moisture and to suppress weed growth, apply a 1 to 2" layer of shredded or chipped wood mulch or pine straw around the planting area. As the mulch decomposes it will add vital nutrients to the soil that your plant will appreciate. Avoid using freshly chipped or shredded wood for mulch until it has cured in a pile for at least 6 months, a year is better. Avoid placing or piling mulch directly against the base of your plant as this could cause the bark to rot.
How To Grow and Care Hibiscus Rose of Sharon
Feeding - Watering - Pruning
How To Fertilize Rose of Sharon
Rose of Sharon are moderate feeders that will benefit from fertilization. We suggest feeding Rose of Sharon in late winter or early spring with a quality slow-release shrub & tree type fertilizer or a natural organic plant food as directed on the product label.
Soil pH - Rose of Sharon grow best in a wide range of soil pH ranging from around 5.5 to 7.5 on the pH scale. Most average garden soils fall between a pH range of 6.0 to 7.0.
Learn More: What is Soil pH and How To Adjust It?
How To Water Rose of Sharon
Note: When watering with an automated irrigation system it's best to set your timer to water during the early morning hours and not in the late evening or at night, which can lead to the onset of fungus and other foliar diseases. During the first few weeks after planting, check soil moisture often and adjust irrigation time if necessary to keep the soil moist, not wet.
At Planting Time
Immediately after planting deep soak the soil in the planting area to a depth equal to the height of the plants root ball. For an extra boost, to stimulate early root formation and stronger root development, you can also water you newly planted Rose of Sharon with a solution of Root Stimulator, which reduces transplant shock and promotes greener, more vigorous plants.
Note: Shrubs planted during the winter dormant season, when plants are not actively growing and evaporation is much slower, will require much less water. So, be extra careful not to overwater during winter!
During the First Growing Season
In average garden soil you should not have to water your newly planted Rose of Sharon every day. More often than not, this causes soggy soil conditions that can lead to root rot and other harmful plant diseases. In the absence of sufficient rainfall, water only as needed to keep the root ball and surrounding soil damp to moist. Keep in mind that deep soaking less frequently, allowing the soil to dry out somewhat before watering again, is much better than splashing just a little water on the plants every day.
When established, Rose of Sharon are quite drought tolerant plants. Only during prolonged periods of summer drought will plants require supplemental irrigation. If you see leaves wilting or falling from the plant during a drought this is a sign your plants could use a deep soaking.
How To Prune Rose of Sharon
Rose of Sharon do not require pruning however respond very well to it. They can be grown as a shrub or lower branches can be removed to form a very attractive small tree.
When to Prune
For shaping purposes or to substantially reduce size, Rose of Sharon can be pruned annually in late winter or early spring, before new growth begins. A stray branch that is spoilinjg the shape of the plant can be pruned any time of year. A damaged or dead branch should be removed when it occurs.
Note: Cease any pruning 2 months prior to the average first-frost date in your area.
How To Prune
Rose of Sharon can be grown as a shrub or formed into a very attractive small tree.
Shaping: For general shaping to keep the plant tidy, you can use a sharp pair of bypass hand pruners to prune branches that have outgrown the rest of the shrub and are spoiling the shape of the plant. Cut these branches back to a point a few inches or so above the main form of the plant. Suckers growing from the base of the plant or leaves growing along the trunks can be removed any time of year.
Tree Forming: To tree form, wait until your Rose of Sharon is about 3 to 4 feet tall. At that time, start at the base of the plant by removing the lateral branches, twiggy growth and leaves growing from trunk(s). Continue removing branches until you've reached the desired height and are satisfied with the appearance. Before making your cuts, make sure that the removal of a branch will not spoil the shape of the canopy. Also, between each cut take a few steps back to take a look at your plant.
Plant Long & Prosper!
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