Learn about hardy hibiscus, including how to plant and grow them. Listen to podcast:
How to Grow: Hardy Hibiscus
Swamp rose mallow
Bloom Period and Seasonal Color
Late summer to fall in colors such as white, pink, red, and bi colors.
Mature Height x Spread
2 to 5 feet x 2 to 5 feet
attracts beneficials, attracts hummingbirds
Yes, you can grow hibiscus in New England. Often people think of the tropical houseplant when I mention this plant, but there is a hardy version that looks just as beautiful. The hardy hibiscus is a slow grower, but it builds size and energy through the summer to finally start flowering in late summer and continue until frost. It puts on quite a show. The flowers are colorful and can be 10 to 12 inches in diameter. They are sometimes called the dinner plate hibiscus for that reason. The plant can grow 5 feet tall and wide filling in an area in the perennial garden. The flowers only last one or two days, but they come in succession keeping the flower show going.
Where, When and How to Plant
Hardy hibiscus is grown throughout our region. You can start seeds indoors 2 months before your last frost date and transplant seedlings into the garden. For just a few plants it may be easier to purchase plants in spring from your local garden center. Plant after all danger of frost has passed and throughout the summer in well-drained, fertile soil. Hardy hibiscus like the heat and full sun, so consider planting them near a south-facing wall or building. Space plants 2 to 3 feet apart in the garden.
Hardy hibiscus like moist soils, so keep plants well watered and mulched with bark mulch to prevent weeds from crowding them and maintain the soil moisture. Fertilize in spring with a layer of compost.
Regional Advice and Care
Hardy hibiscus is slow to emerge in spring in cold areas so be patient. They may not pop out of the ground until June. Pinch the shoots of young plants in early summer to encourage branching and more flower stalks to form. Hardy hibiscus can also self-sow and become weedy. The self-sown seedlings will not necessarily be the same color as the parents, but can be transplanted and moved throughout the garden if so desired. Keep plants deadheaded to look tidy and prevent the seeds from sowing if you don’t want seedlings. Cut back plants after a frost to the ground and compost the flower stalks.
Companion Planting and Design
Plant hardy hibiscus in back of a perennial flower border or among other perennials that have finished flowering such as peonies, iris, and coneflowers. They can tolerate wet soils so are a good choice where Joe-pyeweed and other moisture-lovers thrive.
“Lord Baltimore” is an old fashioned variety with red flowers. “Lady Baltimore” is similar with white flowers and a red throat. “Kopper King” grows 4 feet tall with attractive burgundy colored foliage and pink flowers with a red throat. “Plum Crazy” has frilly pink colored flowers. “Blue River II” has stunning white colored flowers.
I’m not a big fan of gaudy sized and colored flowers, but here’s one I really love. The perennial hibiscus is flowering now throughout our region. Talk about a show stopper. It grows 3 to 6 feet tall and produces whomping 8 to 12 inch diameter flowers until frost.
Unlike its tropical cousin, the perennial hibiscus is hardy to zone 4. It emerges late in spring, but hits its stride in mid-summer putting on growth seemingly overnight. By late summer the flowers start to open in colors such as white, pink, red and lavender. The plant dies back to the ground each winter.
Since perennial hibiscus is a tall grower and fall bloomer be strategic about where to plant it in your garden. Use perennial hibiscus as a focal point in the back of a flower border or mass them along a wall or house for a dramatic effect. Some good varieties to try include ‘Lord Baltimore’, the diminutive Luna Red, Rose or White, or Kopper King. I like Kopper King because the white flowers have a red center and the deeply cut leaves are tinged with bronze.
Plant perennial hibiscus in full or part sun on well drained soil. They’re pretty forgiving plants, but do like a good drink during hot, dry summer weather. Amend the soil with compost annually. In very cold areas or for first year plants, consider mulching the roots in late fall with straw or bark mulch to protect them.
I’ve noticed that perennial hibiscus like to self sow in my garden. After a few years I see new plants popping up among my perennials. However, they all seem to have red flowers regardless of the variety I’m growing.
Now for this week’s tip, do you know when your melons are ripe? Lift cantaloupes off the ground and if the fruit naturally slips off the vine, they’re ready to eat. Check the last tendril or curly curl nearest your watermelon fruit. If it’s dried up, your watermelons are ripe.
From the Vermont Garden Journal.