How To Grow And Care For Summer-Blooming Hibiscuses

When it comes to big, striking blooms, no plant packs quite the punch that hibiscus does. When they bloom, they produce enormous, vibrant blossoms that catch your eye and make you want to look closer. They're some of the showiest flowers in the garden and look positively gorgeous when they begin to bloom, which is why they're such popular summer flowers.

Hardy hibiscus (Hibiscus moscheutos), also known as swamp mallow and rose mallow, comes in a rainbow of colors, from bright red to orange, pink, yellow, and white. Many have deep red centers. Their blooms appear in mid-to-late summer, beginning in June and continuing into fall. According to The New Southern Living Garden Book, hibiscus are "among the showiest flowering plants in Southern gardens. They typically bear funnel-shaped blossoms sometimes as big as dinner plates and often with prominent stamens. The many species offer an astonishing range of flower colors, and most bloom over a long season." They're native to the southern United States, and the biggest hibiscus flowers can reach to 1 foot across. In addition to the pops of color they add to the garden, the flowers also attract butterflies and hummingbirds. Here's how to grow them in your garden.

Hibiscus Care

When caring for hardy hibiscus, ensure that it gets plenty of water during its blooming season. They thrive in full sun and don't start growing until the weather is nice and warm. As a wetland plant, hardy hibiscus can withstand soil that isn't well drained. Hibiscus is usually grown in the ground, but they also make a statement when grown in containers.

Light

Hardy hibiscus can be grown in full or partial sunlight, but the shade should be light if it won't be in direct sun for part of the day. In full sun (at least six hours of direct sunlight a day), the plant will produce more blooms and be more resistant to disease.

Soil

Hardy hibiscus is native to wetlands and creek banks around the southeastern United States. Hardy hibiscus can thrive in wet soil and does best in constantly moist soil that is organically rich. The plant is somewhat salt tolerant and can grow near brackish water. The soil can be loamy, silty, or partially sandy. Plant it in a low area, along a pond, or in a container in rich potting soil.

Water

Give your plant regular, deep waterings during the growing season to keep the soil moist. The leaves can scorch in the sun if the soil is allowed to dry out. It requires less water during the rest of the year, particularly in winter.

Temperature And Humidity

Hardy hibiscus can be grown everywhere in the South except for the Tropical South, which doesn't get chilly enough in winter for the plant to go into dormancy. This plant thrives in a hot, humid climate but requires good air circulation to prevent disease. Hardy hibiscus will die back to the ground after a hard freeze and send up new growth in spring once the weather warms. Sometimes that growth is slow to appear, so make sure to note where you planted it in the garden.

Fertilizer

If you are planting in sandy or heavy clay soil, mix in compost or other organic matter to help retain moisture and enrich the soil. After planting, you can fertilize your hardy hibiscus annually each spring by applying a layer of compost around the plant. You can also use a slow-release fertilizer once a year, but this plant can be sensitive to getting too much phosphorus. Fertilizers are labeled with a ratio of N-P-K (nitrogen, phosphorus, and potassium), so look for a fertilizer with a low middle number.

Types Of Hibiscus

When choosing which hibiscus selections to plant, take into account how much space the mature plant needs. The plant you purchase may look small but grow very large by the end of summer.

• 'Southern Belle' has pale pink flowers with small crimson centers and grows 4-6 feet tall and slightly less wide.
• 'Anne Arundel' has bright pink flowers and grows 4-5 feet tall and slightly less wide.
• 'Lady Baltimore' has soft pink flowers with a large red center, and grows 5 feet tall and wide.
• 'Perfect Storm' and Carousel™ Pink Candy are compact cultivars that grow to about 3 feet tall with pink-veined flowers and red centers.
• 'Cranberry Crush' has intensely scarlet flowers and grows to 4 feet tall and wide.
• 'Raspberry Rose' has bright raspberry red flowers and can reach 7 feet tall and 10 feet across.

Pruning

Hardy hibiscuses don't require pruning, but pinching the plants back in early summer will produce more compact, bushier growth. When the stems reach at least 6 inches tall, cut back no more than half the growth, pinching just above a set of leaves. If you like, you can do this two or three times before the 4th of July.

You can remove spent flowers to tidy up the plant or trim back stems by a third after they flower to encourage more growth. The plant will freeze to the ground in winter. In early spring before new growth appears, cut back the dead, woody stems to 4-6 inches above the ground.

Propagating Hardy Hibiscus

Hardy hibiscus can easily be propagated with cuttings during the growing season. You'll want to use firm young stems rather than the soft green growth at the tips:

1. Prepare small pots with a moist mixture of peat moss and sand or peat moss and vermiculite.
2. With a pair of sterile pruners, cut pencil-thick, firm young stems in sections 5 to 6 inches long. Cut off any green growth at the tip and strip off the lower leaves from the stems, leaving a pair of leaves at the top.
3. Dip the bottom of each stem in rooting powder, then stick one cutting 3 or 4 inches deep in each pot. Water to keep moist.
4. You can place the pots outdoors in full shade to soak up the humidity or keep them indoors, covering each pot with a clear plastic dome (the top of a 2-liter soda bottle can work well) until the plants begin to root and grow in four to six weeks. It can take two or three months for the root system to become established enough to repot or transplant your hibiscus.

How To Grow Hardy Hibiscus From Seed

Hardy hibiscus can be grown from seed, though the resulting plants may not look like the original you have growing in your garden. You'll need to give your hibiscus a head start to have it ready for the growing season. Start your seeds indoors 6-12 weeks before the last frost. The seeds germinate best in warm temperatures, so grow them in a room that stays at about 75 degrees Fahrenheit. Here's how to do it:

1. Soak your seeds in room temperature water overnight to help with germination.
2. Fill a seed-starting tray or small pots with a commercial seed-starting mixture and moisten.
3. Plant seeds 1/4 inch deep and water. Cover with clear plastic wrap or a dome to help conserve moisture.
4. In 14-21 days, seedlings should emerge. Move your tray or pots to a sunny window or under fluorescent plant lights. Remove any plastic.
5. As your plants grow, transplant them to larger pots if needed. Fertilize with a water-soluble houseplant fertilizer at half strength when the plants are about four weeks old.
6. Harden off plants outdoors for a week before transplanting once all danger of frost has passed. Place in a sheltered spot and gradually increase sun exposure.

Potting And Repotting Hardy Hibiscus

Hardy hibiscus can be grown in containers, but some grow quite wide and will need repotting during the growing season. Start by choosing a container one size wider than the nursery pot. Use one with a drainage hole so that rainwater won't be trapped. Fill it partway with high-quality potting soil that is rich in organic matter, place your plant at the same level it was in its nursery pot, and fill in around the plant with potting soil. Make sure to water your container regularly to keep the soil damp—hardy hibiscus requires consistently moist soil. You can place a tray underneath the container to conserve water, especially during hot, dry weather. Repot your plant in a larger container if roots begin to emerge from the drainage hole or the soil stops retaining moisture.

Overwintering

This plant is hardy throughout the South and generally doesn't require extra winter protection. Cut stems back to a few inches above the ground after the foliage dies. You can add a few inches of mulch or straw around the plant if you are expecting an extended hard freeze.

Common Pests & Plant Diseases

The foliage of hardy hibiscus can be severely damaged by Japanese beetles or the smooth, green caterpillars of sawflies. Pick them off and dunk them in a can of soapy water. Pesticides are most effective on sawfly caterpillars when they are small. Use insecticidal soap or spray foliage with a pesticide containing spinosad (Bt does not work on sawfly larvae). Hardy hibiscus can be affected by leaf spots from various fungi. Avoid overhead watering to reduce the spread and clean up and dispose of fallen leaves.

How To Get Hardy Hibiscus To Bloom

Depending on where you live, it's common for hardy hibiscus to hold off blooming until late summer. The plant blooms best in full sun, so increase sun exposure if you think that might be a factor. Also, make certain the soil is moist at all times to support the growth of the plant. Hardy hibiscus blooms on new growth, but pinching the plants too late in summer or pruning severely can delay blooming.