Posted 21 March 2012 - 07:10 AM
Eric, hopefully you'll get an answer from someone closet to your conditions, but I do grow it here in Berkeley, California, and have seen it growing in Oaxaca and Puebla states in southern Mexico. In habitat it grows best in cloudforest locations with those daily afternoon fogs, but I've also seen it growing as an escaped weed seeding itself at the edge of the asphalt highway in desert conditions with cactus. No larger mature plants to be seen there, so I doubt they survive such hot dry locations during the long term.
They are in bloom here right now, and easily tolerate our typical winters which only flirt with freezing, but burn foliage at/below 0°C. As you probably are already aware, after the second or third year they can start to spread vigorously from the roots. A large hillside planting of Wigandia up at the UC Berkeley Botanic Garden has taken over a 300 foot wide slope, so be warned what it is capable of.
What I'm not certain of is how Wigandia tolerates high summer night time temperatures, as I've only seen it at higher elevations in Mexico. It is a cool looking very large shrub/tree, the foliage can get up to 3 feet long, and bloom period here lasts up to 3 or 4 months. The downsides are potential invasive habit and heavy seeding in summer rainfall climates, and the stinging/itchiness factor of the foliage and stems. It seldom sets viable seed here in Berkeley, but I have had some volunteer seedlings show up in well watered containers in proximity to the Wigandia. It has also naturalized in north/east facing canyons of oak woodlands/chaparral vegetation in Los Angeles. I've never seen it escape here in the SF Bay Area, lack of pollinators and freezes as well as 6 month long dry season in the warmer months probably limit its spread. It has been easy and fast growing for me, with clay loam soils or even thin rocky slopes with some supplemental summer irrigation, it is relatively drought tolerant here under cool summer weather with coastal fog.