Garden Guide: How to grow hardy hibiscus
Few plants bring the tropical feel like a hibiscus. They are planted in tropical climates across the world and are the state flower of Hawaii. That's why it may come as a surprise that some, like the Rose Mallow Hibiscus, are native to the Northeast United States and thrive in our climate.
The most common hibiscus for sale is Hibiscus rosa-sinensis. They're beautiful but are frost sensitive and are usually sold as summer annuals. The Rose Mallow Hibiscus, known botanically as Hibiscus moscheutos, can be harder to find for sale, but are worth looking for. They bloom for months and come back every year.
Rose Mallow Hibiscus flowers look similar to their tropical hibiscus cousins, but are much larger. It's very common for Rose Mallow blooms to reach a foot across! That’s how they got their other nickname, the "Dinner Plate Hibiscus". There are hundreds of varieties of Rose Mallow hibiscus, with white, red, or pink flowers. They come in many shapes and sizes and can fit in any yard. The smallest grow only 2 feet tall, and the largest reach more than 8 feet tall.
How to grow:
Perennial Hibiscus are one of the last plants to emerge in the spring, usually in late June in our climate. They're often overlooked because they are not available at local nurseries until the middle of the summer. While these plants are slow to wake up early in the season, they don't waste any time. Perennial Hibiscus only take a month to grow to full size. The blooms typically start by August. Some of the newer perennial hibiscus varieties bloom from mid-summer until the first freeze of the season. The blooms only last a single day, but new blooms are constantly opening up.
Unfortunately, these do not make good houseplants. They require a few months of cold weather to rest up for the next season. That is what makes them perfect landscape plants in our climate. These "tropical fakers" can’t get enough of our four seasons! Gardeners who don't have a spot in the ground can use these as container plants. They will come back every spring, even if the container freezes solid during the winter.
Rose Mallow Hibiscus require a lot of water and sunshine to look their best. Although they can bloom well in part-shade, they bloom their best in full sunshine. The blooms fall off on their own and no pruning is required. During the winter, all the branches above the ground can be cut back. This will not affect the plant in any way because the only part of this hibiscus species that stays alive during the winter is tucked away underground.
Rose of Sharon (Hibiscus syriacus)
This hardy Hibiscus species needs a category of its own. The Rose of Sharon is very popular and pretty, but it can be a problem for gardeners.
Hibiscus syriacus is not native to North America and has been declared invasive in some parts of the country. They have smaller flowers than our native hibiscus, and grow much taller because they do not die back to the ground each year.
Seed pods cover Rose of Sharon plants every Autumn and hundreds of seedlings sprout the following year. There are some cultivars that are supposedly unable to produce seedlings, but gardeners should exert caution before planting these.