The scarlet rosemallow (Hibiscus coccineus) is native to the southeastern parts of the USA. It is found near marshes, swamps, and other moist areas, so in the garden, it does well near streams or water features. As it is tall-growing, it is wise to stake it.
I. Appearance and Characteristics
Hibiscus coccineus, the scarlet rosemallow, is a hardy Hibiscus species, also known as Texas star, brilliant hibiscus and scarlet hibiscus.
The plant is found in swamps, marshes and ditches on the coastal plain of the Southeastern United States. It is native from Southeastern Virginia south to Florida, then west to Louisiana. Despite its common name Texas star, the plant is not found naturally in Texas. In addition to the scarlet-flowering variety, a white-flowering variety is also known as the white Texas star or lone star hibiscus.
H. coccineus is a herbaceous perennial (it dies back during the winter) and grows 6–8 ft (1.8–2.4 m) tall. The palmately compound leaves are 5–6 in (13–15 cm) wide, and look much like those of the hemp plant, Cannabis sativa. It features bright scarlet flowers that have five petals and are reminiscent of hollyhock. These flowers are attractive to hummingbirds, butterflies and bees, including the specialized bee Ptilothrix bombiformis. The plant prefers to be grown in full sun with moist soil. It is hardy in USDA hardiness zones 6–9.
The Latin specific epithet coccineus means “coloured or dyed scarlet”. The genus name is the Greek and Latin name for “mallow”.
II. How to Grow and Care
Sunlight
Swamp hibiscus does best in full sun or partial shade. It can survive in shadier positions, but this usually means the stems will grow overly long and thin, and it will be more prone to collapsing. The blooms that appear aren’t likely to be as impressive either.
Temperature and Humidity
This plant prefers hot and humid summers. If you live in a more temperate region, making sure it has a good layer of mulch during the winter will help promote new growth the following season.
Even with mulch, this plant isn’t suited to areas that are prone to harsh freezing winter conditions.
Swamp hibiscus can be susceptible to windburn. For this reason, and because of its height, positioning it in a sheltered position is recommended.
Watering
The key to success with the swamp hibiscus is to ensure that it’s kept moist during the growing season. From spring right through to fall, it will need regular watering.
Although it will only need very limited watering in the winter, it’s still best not to let the soil dry out completely.
Soil
Scarlet rosemallow like slightly acidic, moist, well-drained soil with a pH value of 5.5-7. If the soil is sticky and heavy, coarse sands may be added to improve permeability. In the case of slightly alkaline, chalky soil and lime soil, add rotten leaf soil, peat soil, or completely decomposed garden compost along with sulfur fertilizer until the pH value reaches an appropriate range.
Fertilizing
Adult plants do not require frequent fertilization, but flowering plants are best fertilized annually. In early spring, granular or powdery slow-release fertilizer should be mixed into the soil around the aboveground part of the plant, generally 60-70g/m2. Scarlet rosemallow prefers potash fertilizer rather than phosphate fertilizer. Newly planted plants may also require additional, quick-acting, liquid fertilizer weekly.
Planting Instructions
The best planting season for scarlet rosemallow is during fall while it is still warm. This allows the root to recover in warm soil, encouraging vigorous growth the following year. A location that receives sufficient sunlight and is slightly shaded in the afternoon is best for planting scarlet rosemallow, depending on the local sunshine projection. All weeds should first be removed before planting, and then a planting pit can be dug. The pit should be at least twice the diameter of the root ball and attached soil, and slightly deeper than the root ball’s height.
For potting, try to choose a dwarf variety and the largest flowerpot possible. The flowerpot should be of sufficient weight and stability, with stone pots preferred. Pot depth should be at least 1.5 times the depth of the root ball. The diameter should be 1/6-1/4 of the height of the adult plant. Place 3 cm of rough stones at the flowerpot bottom for better drainage.
Sort and scatter the root ball, place it in the flowerpot or planting pit, and then gradually backfill and compact the soil. Cut off any diseased, damaged, inward-growing, or crossed branches and other branches that affect the plant’s shape. Water thoroughly and spread a 5 to 7 cm layer of decomposed medium or crushed bark. If the plant is a standard seedling type with a single trunk, insert a stake before planting to support the plant.
Pruning
Scarlet rosemallow generally does not require pruning. If desired, however, it should be pruned in early spring. Keep 2-4 buds on each branch grown the previous year and cut off any dead, diseased, or weak branches. For shrub shaping, trunks should be pruned to different heights, creating a sense of levels. For tree shaping, the lateral branches at the lower trunk should be removed and the upper lateral branches should be shortened.
To restore old branches, prune after blooming in fall. Each trunk should be shortened to a height of 30 to 46 cm. Afterward, apply a slow-release fertilizer. In the next growing season, keep 2-4 stronger, new branches on the trunk.
Propagation
Propagating swamp hibiscus from cuttings is easy. Look for a plant with five or more stems coming out of the ground for your cutting. Here’s how to propagate swamp hibiscus with cuttings:
- Take a 6-inch cutting from a healthy plant in the spring.
- Dip the cutting in the rooting hormone.
- Press the cutting 3 inches into a container filled with peat moss.
- Keep it moist and out of direct sunlight either indoors or outdoors.
- When new leaves start to appear, the cutting can be transplanted to its permanent position.
How to Grow Swamp Hibiscus From Seeds
Swamp hibiscus grows well from seeds. If you’re collecting seeds from your existing plants, wait until the seed pods at the base of the flowers turn from green to brown. The seeds within can be removed from the pods and stored until the early spring.
- Scrape seeds with sandpaper or a nail file so they will germinate faster.
- Soak in warm water for a minimum of an hour to soften.
- Sow into moist potting soil.
- The seedlings will do well in a sunny position.
- Keep soil moist.
- Germination should take about two weeks.
- Transplant the seedlings to their permanent position after the last spring frosts are passed.
Potting and Repotting
Swamp hibiscus does well in pots. If mixing in a large container, use it as the center showpiece. Place pots outdoors or even in shallow areas of ponds. Since this plant needs consistent moisture, opt for good quality potting soil. The plant will not bloom in dry soil.
Overwintering
In cooler regions, swamp hibiscus may survive outdoors over winter with a good cover of winter mulch. Limit watering the plant during cool months. The plant does not need to be taken indoors for the winter.
Pests and Diseases
Common Pests & Diseases
Although this is a hardy plant, pests such as aphids can sometimes be an issue. Sometimes it can be enough to spray cold water on the leaves to remove the insects. Insecticidal soaps can also be effective.
Plants with woody stems, like the swamp hibiscus, can sometimes be prone to a fungal disease known as rust. Orange spots, similar to the color of rust, can begin to appear on the leaves.
These sections should be removed by pruning. If the problem isn’t cleared up by winter, cutting the stems right back to the ground will eliminate the issue. New and fungal-free growth should appear the following season.
Common Growing Problems
Yellowing Leaves
Yellowing leaves on your swamp hibiscus can be indicative of a water issue. Too much or too little water can often cause this, so ensure your plant gets the optimal amount (consistent moisture).
Dropping Leaves
If you notice your swamp hibiscus’s leaves dropping, it could be due to drastic changes in temperature. This plant thrives in warm, humid conditions, so too little humidity, extreme cold, or high heat could cause leaf drop. Poor drainage and not enough light can also cause this.
Find Where to Buy the Best Scarlet Rose Mallow (Hibiscus coccineus)
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