This document is a part of a series that was originally written by Edward F. Gilman.
Introduction
Seaside joyweed is a native drought- and salt-tolerant herbaceous groundcover (Figure 1). This plant has small, succulent evergreen leaves (Figure 2). Inconspicuous yellow and white flowers are produced at the nodes (Figure 3). This species can be found in coastal and hammock ecosystems in south Florida. It is generally not considered a common landscaping plant but may be found at certain native plant nurseries. Stems creep along the sand, rooting at the nodes and sending up new shoots. The plant quickly covers an area in this manner, growing to about 6 inches tall, and may reseed itself in consecutive years. It is well suited as a groundcover or may cascade when planted near the edge of a wall. This plant is also suitable for coastal landscaping, dune stabilization, and habitat restoration.
Credit: © Joe Benjamin, some rights reserved (CC-BY-NC) via iNaturalist
Credit: Jade Fortnash, no rights reserved (CC0) via iNaturalist
Credit: © James K. Wetterer, some rights reserved (CC-BY-NC) via iNaturalist
General Information
Scientific name: Alternanthera maritima
Pronunciation: al-tur-nan-THEER-uh muh-RIT-tim-uh
Common name(s): Alternanthera
Family: Amaranthaceae
Plant type: herbaceous; groundcover
USDA hardiness zones: 9A through 11B; in coastal areas (Figures 4 and 5)
Credit: This map is based on the 2023 USDA Plant Hardiness Zone Map. Visit https://planthardiness.ars.usda.gov/ for specific zone information.
Credit: This map is based on the 2023 USDA Plant Hardiness Zone Map. Visit https://planthardiness.ars.usda.gov/ for specific zone information.
Planting month for zone 9: year-round
Planting month for zones 10 and 11: year-round
Origin: native to Florida
Uses: groundcover; cascading down a wall; habitat restoration; coastal landscaping
Availability: somewhat available, may have to go out of the region to find the plant
Description
Height: 0.5 to 1 foot
Spread: 2 to 3 feet
Plant habit: spreading
Plant density: moderate
Growth rate: fast
Texture: medium
Foliage
Leaf arrangement: opposite/subopposite
Leaf type: simple
Leaf margin: entire
Leaf shape: elliptic (oval)
Leaf venation: pinnate
Leaf type and persistence: evergreen
Leaf blade length: less than 2 inches
Leaf color: green
Fall color: no fall color change
Fall characteristic: not showy
Flower
Flower color: white, yellow
Flower characteristic: inconspicuous and not showy
Fruit
Fruit shape: irregular; utricle
Fruit length: less than 0.5 inch
Fruit cover: dry or hard
Fruit color: brown
Fruit characteristic: inconspicuous and not showy
Trunk and Branches
Trunk/bark/branches: not applicable
Current year stem/twig color: green
Current year stem/twig thickness: medium
Culture
Light requirement: plant grows in full sun
Soil tolerances: acidic; slightly alkaline; sand; loam; well-drained
Drought tolerance: high
Soil salt tolerance: good
Plant spacing: 36 to 60 inches
Other
Roots: not applicable
Winter interest: no special winter interest
Invasive potential: may self-seed each year
Pest resistance: long-term health usually not affected by pests
Use and Management
Seaside joyweed is a hardy native plant that tolerates nutrient poor, sandy soils. It is also highly drought tolerant and exhibits salt tolerance, making it a suitable plant for coastal landscaping. This plant thrives when planted in full sun. Plant on 3- to 4-foot centers to quickly establish a dense groundcover. The moderately thick stems will cascade and cover a wall nicely when planted near the edge.
Design Considerations
Seaside joyweed serves as a textural groundcover that complements and enhances the features of its companions. For a classic coastal dune look, combine it with plants that offer strong vertical contrast. An effective pairing is with sea oats (Uniola paniculata). The tall, graceful, and swaying habit of the sea oats rising directly from the dense, silvery-green mat of the seaside joyweed creates a dynamic and resilient composition that is the very definition of a stable dune ecosystem.
To introduce a bolder texture and form, plant seaside joyweed around the base of saw palmetto (Serenoa repens), particularly the silver variety. The fine, delicate foliage of seaside joyweed creates a soft foundation that contrasts beautifully with the palmetto’s large, rigid, fan-shaped fronds. For a splash of color, allow beach sunflower (Helianthus debilis) to weave through the seaside joyweed. Both are low-growing, salt-tolerant spreaders, but the sunflower's bright yellow daisy-like flowers will appear to float atop the fine-textured carpet of the seaside joyweed, creating pockets of seasonal color and interest without appearing messy.
Pests and Diseases
No pests or diseases of major concern.