Hibiscus flowers are tropical icons. Their colorful blooms feature not only in tropical gardens, but just about any form of tropical-themed product you could think of. The dinner plate hibiscus is true to its name, with beautiful flowers that reach an average of 7-9in / 18-23cm wide. Yes, they really are the size of dinner plates!
In some areas this plant goes by the common name of rose mallow, swamp mallow, crimson-eyed mallow and swamp rose mallow. As a herbaceous perennial, Hibiscus moscheutos varieties grow into large bushy plants. The dinner plate hibiscus can reach heights and widths of up to 6 ft (1.8 m) or 3 ft (0.9 m) for dwarf varieties.
Between different varieties, the diameter of individual flowers can vary from 2-12 in (5-30 cm). Leaves are large and generally mid-dark green but some varieties can feature leaves with bronze or purple tints. They will develop a saw-tooth or serrated margin as they mature.
These are hardy hibiscus plants suitable for USDA zone 4-9. This is great news for gardeners who are looking for tropical-style plants for cold climates. Dinner plate hibiscus will tolerate some salinity so is also useful in coastal locations1.
Dinner plate hibiscus is known for its showy flowers. Different varieties demonstrate one of two possible blooming patterns. Determinate blooming varieties form flowers on the tips of mature branches. They will have fewer flowers overall with most flowers at the top of the plant. Indeterminate flowering varieties will produce flowers at any point along stems. This means they produce a greater number of flowers distributed all over the plant. On average, an indeterminate variety will produce three times as many buds as a determinate blooming variety.
What you can expect from a dinner plate hibiscus
Flowers are produced from mid summer to late fall (autumn). Traditional colors are white, pink and red however, hybrid varieties are available in shades of lavender and blue2. Flowers may be a solid color or have a contrasting eye in the center. An example is H. moscheutos ‘Luna White’, which has white flowers and a red eye. Just like all hibiscus, it has five large petals that are closely arranged to form a large flower head.
After flowering and as winter approaches these plants will drop all foliage and flowers and stems will die back. Afterwards all that remains is the crown at the base of the plant and the root ball. Despite this appearance it isn’t dead, it’s just protecting itself over the cold winter. As much as you might think otherwise, you can count on it to return the following spring.
In early spring new growth emerges from the soil, signalling the beginning of the growing season. For the next few months it will grow rapidly. When mid summer arrives flower buds start to appear and before long you’ll have open flowers. It will bloom continuously throughout summer and early fall. You can expect new flowers until the days shorten. Eventually flower production stops after the fall equinox. Keep the new flowers coming by removing the spent blooms (deadheading). This will stop the plant from putting energy into producing the ‘fruit’ and seed and redirect efforts into producing beautiful new blooms instead.
Best potting soil and fertilizer for dinner plate hibiscus
The ideal growing medium for H. moscheutos varieties is 4 parts pine bark to one part vermicompost, with a potassium (K) fertilizer added4. You really only need to go to this effort if you are growing plants to sell commercially or for competition. Other standard or premium potting soils and blends will produce a healthy flowering plant. If you are growing your dinner plate hibiscus in the garden it will grow in any fertile soil.
Add an all-purpose slow-release fertilizer when growth starts in spring. Then 6-8 weeks later add a rose fertilizer (or any other flower-boosting fertilizer) to support flower production over the summer. The all-purpose fertilizer supports healthy new growth both above ground and at the root level and the the flower boosting fertilizer helps the plant to produce the stunning blooms it is grown for. Importantly, don’t add the flower-boosting fertilizer too early. If you do the plant won’t get the higher level of nitrogen it needs to produce the healthy stems and foliage that will give you larger flowers in the long term.
Only apply fertilizer at the rate advised because adding extra fertilizer can be bad for your plants. If your plants are near a body of water the extra fertilizer can enter the water through runoff and cause damage to aquatic plants. It can also cause excessive algal and bacterial growth which consumes oxygen in the water. Subsequently this leads to death of fish and other water life.
Selecting a location to grow your dinner plate hibiscus
In general, rich soils, enough water and lots of sunlight are the keys to successfully growing dinner plate hibiscus. Given that it is native to marshes and swamps of the east coast of North America it needs a moist soil. Accordingly, it will grow in wet soils quite happily. Wilting leaves or dropping leaves and flowers are early signs of insufficient water.
The preferred aspect is full sun as H. moscheutos varieties are generally considered long-day plants. This means that they achieve optimal plant mass and flowering with 16 hours per day of sunlight. Therefore, plants grown in partial shade or full shade locations will not produce as many leaves and if in full shade may not flower3. This is the reason that dinner plate hibiscus flowers later in the summer and fall as it needs the longer days to get enough light to produce flowers. For example, in higher latitudes that have longer hours of daylight it may develop flowers in early summer.
How to propagate dinner plate hibiscus
To get a plant with identical flowers to the parent, softwood stem cuttings taken in late spring through to early summer will give you the best success rate. There are alternative ways to propagate these perennial plants including division and seed. Dinner plate hibiscus plants can be grown from seed however many commercial hybrid varieties won’t produce seed. Growing a dinner plate hibiscus from seed doesn’t guarantee that the new plant will be the same as the parent.
Propagating dinner plate hibiscus from cuttings
To grow from cuttings firstly take sections while the plant is actively growing and make sure each has at least one leaf node. Then remove the leaves and dip the cutting in a hormone powder or gel. Following this make a hole in the seed raising medium using a dibbler (or the end of a pencil works fine) and then place the cutting in the hole. Keep it moist and warm, in a position where it receives good indirect light. You will see new growth will emerge from the leaf node within 2-4 weeks. Meanwhile if any of the cuttings die or have signs of rot remove and dispose of them.
Dividing dinner plate hibiscus plants
If you have a large mature plant you can divide it in late winter by digging up the root ball and separating it into new sections. Firstly, trim stems down to about 6-8 in (15-20 cm) and dig out the root ball. Next wash soil off the roots and then with a clean sharp spade or knife divide the root ball into two even sections. Immediately replant each section so that they settle ready to for their growth phase in spring.
How to grow dinner plate hibiscus from seed
To grow from seed collect the dried seed pods in fall and store them in a paper bag or envelope until late winter. When you are ready to start, the outer coating of the seeds needs to be scarified or soaked to support germination. To do this you can use a small blade such as a scalpel or razor to nick the coating. Alternatively, heat water to 75 oC/ 167 oF and add the seeds. Let the water cool to room temperature (at least 20 oC / 70 oF) and leave the seeds to soak for 12-24 hours.
Next plant the seeds in trays of seed raising mix and cover them thinly. Keep the mix moist and warm, and seedlings will begin to emerge in 4-6 days. Allow up to 10 days if using the soak method. After 2-3 weeks the seedlings can be transplanted into small pots or plug trays. Another 2-3 week wait will see new foliage begin to develop. Finally, by summer you will have a small plant that can be planted out into the garden. If you aren’t ready to plant it out yet you can keep it in the pot ready to be planted out in the following spring.
Pests and diseases
Root rot may be a problem in areas where cotton is grown as dinner plate hibiscus is susceptible to cotton root rot (Phymatotrichum omnivorum). It is also prone to wilt, crown and root rot caused by Fusarium sp5. Other pests include Japanese beetles, sawflies, spider mites and aphids.
As with many plants that grow in humid environments it may also get leaf spot. This is a fungal disease so can be treated with an anti-fungal spray but can also be prevented by not letting plants get overcrowded. Prune stems or if you have a large plant remove some branches with a strong pair of loppers to allow good air circulation around the leaves.
Popular dinner plate hibiscus varieties include:
Other forms of hibiscus that you might like are:
Hibiscus rosa-sinensis or Hibiscus syriacus (both may be known as Rose of Sharon).
In summary:
The best place to grow perennial hibiscus plants to enjoy bloom after beautiful bloom is in full sun, with a rich moist soil. Use an all-purpose fertilizer in early spring then in late spring switch to a flower-boosting fertilizer. Deadhead flowers to promote repeat flowering then prune back in winter.
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References:
1 Feng, X., Hussain, T., Guo, K., An, P., & Liu, X. (2021). Physiological, morphological and anatomical responses of Hibiscus moscheutos to non-uniform salinity stress. Environmental and Experimental Botany, 182, 104301.
2 Malinowski, D. P., Brown, R. S., & Pinchak, W. E. (2012). ‘Blue Angel’Winter-hardy Hibiscus (Hibiscus× moscheutos L.). HortScience, 47(2), 289-290.
3 Warner, R. M., & Erwin, J. E. (2003). Effect of photoperiod and daily light integral on flowering of five Hibiscus sp. Scientia Horticulturae, 97(3-4), 341-351.
4 McGinnis, M. S., Warren, S. L., & Bilderback, T. E. (2009). Replacing conventional nursery crop nutrient inputs with vermicompost for container production of Hibiscus moscheutos L.‘Luna Blush’. HortScience, 44(6), 1698-1703.
5 Lupien, S. L., Dugan, F. M., Ward, K. M., & O’Donnell, K. (2017). Wilt, crown, and root rot of common rose mallow (Hibiscus moscheutos) caused by a novel Fusarium sp. Plant Disease, 101(2), 354-358.
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