Perennial Plants for Wet Areas

(News article for December 5, 2020)

This is southeastern Louisiana, where we have, on average, about 60 to 65 inches of rainfall each year.

While some areas of Tangipahoa and Washington Parishes have fine sandy loam topsoil and a water table (where soil stays saturated for an extended period) well below the surface, other areas have a heavier soil texture and a water table within a few inches of the surface. Even in relatively well-drained areas, there are often low spots or areas where, for example, water drains off the roof and soil stays wet much of the time.

Plants not suited to wet conditions often develop root rot or just don’t grow well in wet areas. Thankfully, we have options for wet spots.

There are certainly trees and shrubs suited to wet areas, but in this article I’m going to focus on some herbaceous (non-woody) perennial plants.

Louisiana irises include five iris species and hybrids among them. Flowers of three of the five species – I. brevicaulis (zigzag iris), I. giganticaerulea (giant blue iris), and I. hexagona (dixie iris) – commonly have “LSU colors,” or purplish sepals with yellow in the center. Iris fulva (copper iris) flowers typically have rusty red coloration. Iris x nelsonii (Abbeville iris) is believed to have resulted from crossing of other Louisiana iris species and can have flowers of a variety of colors.

A perk of Louisiana irises is that they have green leaves during the winter, unlike many herbaceous perennials. Active growth occurs between October and April, they bloom in March and April, and leaves tend to die back during the summer. August through early October is a good time to divide and transplant them.

Plant these in an area that gets at least six hours of sun per day for good flower production.

Southern blue flag iris (I. virginica) is another native iris suited to wet areas. Like some of the Louisiana irises, these produce purple to blue flowers with yellow coloration in the middle of the sepals in the spring.

Another flowering plant for wet areas is the southern swamp lily (Crinum americanum). This is the US’s only native Crinum species. This amaryllis relative grows to approximately 2 feet tall. They produce distinctive white flowers with six elongated petals and contrasting purple stamens between spring and fall.

Hymenocallis liriosme is another amaryllis family member that is sometimes called swamp lily or swamp spider lily. Like Crinum americanum, the flowers have six narrow white petals, but they also have a white membrane that connects stamens and resembles another whorl of petals.

Note that plants in the Lycoris genus are also called spider lilies, as well as naked ladies, surprise lilies, and hurricane lilies. Unlike Crinum americanum and Hymenocallis liriosme, Lycoris spp. plants are not wetland plants.

Some cold-hardy hibiscus species are well-suited to wet areas.

The Texas Star hibiscus or scarlet rose-mallow (Hibiscus coccineus) can reach 10 feet tall and wide and produces striking five-petaled red flowers in summer and fall. It dies back in winter and comes back from the roots. The leaves look like those of Cannabis sativa, so be prepared for some teasing from your neighbors.

Plants of crimsoneyed rosemallow or swamp rose-mallow (Hibiscus moscheutos, sometimes called “dinner plate” hibiscus) are available with flowers of a variety of colors. Like Texas star hibiscus, these die back in winter and come back from the roots. While the species can grow to 4 to 7 feet tall, cultivars in the Luna series only reach about 3 feet.

Finally, the rushes (Juncus spp.) are generally adapted to wet areas. Common or soft rush (Juncus effusus) and needlegrass rush or black needlerush (J. roemerianus) are two that are native to Louisiana wetlands. The round stems of these can reach approximately 5 feet tall.

Let me know if you have questions.

Contact Mary Helen Ferguson.

20180915_111403-cropped2jpgCrinum americanum blooms in Hammond Research Station’s rain garden (September 2018). (Photo by M.H. Ferguson)

12/10/2020 9:31:52 PM
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