Introduction

Porterweed is a small perennial shrub that becomes woody toward the base of the stem as is grows to about one year old. Plants grow about 4 feet tall by 6 feet wide before stems droop and touch the ground. Blue or pink flowers are borne terminally on long, stringy spikes at the ends of the stems. They attract butterflies to the landscape. Rich, dark green foliage displayed on square, green stems makes porterweed a nice addition to any sunny landscape.

General Information

Scientific name: Stachytarpheta cayennensis

Pronunciation: stake-kee-tar-FEE-tuh 

Common name(s): blue porterweed

Family: Verbenaceae

Plant type: shrub; perennial; herbaceous

USDA hardiness zones: 10 through 11 (Figure 1)

Planting month for zone 10 and 11: year round

Origin: not native to North America

Uses: hedge; border; mass planting; attracts butterflies

Availability: somewhat available, may have to go out of the region to find the plant

Description

Height: 4 to 8 feet

Spread: 4 to 8 feet

Plant habit: round

Plant density: dense

Growth rate: fast

Texture: medium

Foliage

Leaf arrangement: opposite/subopposite

Leaf type: simple

Leaf margin: serrate

Leaf shape: ovate

Leaf venation: pinnate; reticulate

Leaf type and persistence: semi-evergreen

Leaf blade length: less than 2 inches

Leaf color: green

Fall color: no fall color change

Fall characteristic: not showy

Flower

Flower color: pink; blue

Flower characteristic: summer flowering; fall flowering

Fruit

Fruit shape: unknown

Fruit length: unknown

Fruit cover: unknown

Fruit color: unknown

Fruit characteristic: inconspicuous and not showy

Trunk and Branches

Trunk/bark/branches: not particularly showy; typically multi-trunked or clumping stems

Current year stem/twig color: green

Current year stem/twig thickness: thin

Culture

Light requirement: plant grows in part shade/part sun

Soil tolerances: acidic; alkaline; sand; loam; clay

Drought tolerance: high

Soil salt tolerances: unknown

Plant spacing: 36 to 60 inches

Other

Roots: usually not a problem

Winter interest: no special winter interest

Outstanding plant: plant has outstanding ornamental features and could be planted more

Invasive potential: not known to be invasive

Pest resistance: long-term health usually not affected by pests

Use and Management

Porterweed is frequently used in a mass planting along a foundation, or as a clipped or natural unclipped hedge to provide continuous color to the landscape. Space plants about 3 to 4 feet apart. A row will maintain a nice uniform shape for 6 or more months without pruning. Regular clipping can maintain a uniform shape for more than a year before the plant needs to be cut back to thicken the growth. Unclipped plants begin to open up as stems droop to the ground. For this reason, they are usually cut back each year, or any time the plant becomes leggy. This allows new growth to fill in and thicken the plant.

Locate porterweed in a sunny location in any soil. Provide irrigation during establishment and then in extended drought in the summer. Fertilize about twice each year to maintain foliage color and provide for continuous growth.

Pest and Diseases

No serious pests or diseases are known to affect porterweed.