Blue Porterweed (Stachytarpheta cayennensis) is part of the Verbenaceae family. The bright green leaves have a quilt-like appearance and a toothed leaf margin. Small deep blue to purple flowers appear starting at the bottom of the bloom spike and extending up towards the top of the spike over time. The purple blooms appear throughout the year and the plant grows to about 3-4′ in height. Blue Porterweed is salt tolerant and relatively drought tolerant making it a good fit for our island environment.
Blue Porterweed does well in full sun to light shade and is native to the American Tropics. Its growth pattern is more sprawling than upright and looks particularly good in a casual garden setting. Mixed with other butterfly plants its blue/purple flowers and dark green leaves make an attractive border planting or as a mass planting with other mixed butterfly flowering plants to create a cottage-style garden. Other interesting names this plant goes by are Blue Snakeweed, Verbena Azul and Cayenne Snakeweed.
This plant is a must for every butterfly garden and you are sure to find it at most butterfly conservatories. Its deep blue to purple flower spikes provide a consistent source of nectar throughout the year, attracting butterflies such as the Gulf fritillary, Monarch and large Orange Sulphur. It is also a larval host plant for the Tropical Buckeye caterpillar. This plant attracts, bees, moths and beetles all of which beneficial to the garden.
Technically, Blue Porterweed is a perennial, although with proper pruning it can last for 3-4 years. It is a good practice to cut this plant back each year or anytime it gets too leggy so the new growth can fill in and create a fuller plant. This plant is self-seeding and most seedling will come up in the spring or early summer. You can also propagate it from stem cuttings. There are 2 other species that do well in South Florida also, a lighter blue version Stachytarpheta jamaicensis and a Red Porterweed, Stachytarpheta mutabilis.
There are very few plants in our tropical plant palette that have deep blue/purple blooms. Blue Porterweed brings that striking contrast into the garden to offset the reds, oranges and yellows so prevalent in tropical landscapes. Plant this in your butterfly garden or put some in a pretty piece of pottery and attract more butterflies to your yard.
This column is a joint effort by all at In The Garden, Sanibel’s local garden center located at 3889 Sanibel Captiva Road, Sanibel Island, Florida.