Ask Mr. Smarty Plants

There are about six (depending on how taxonomists group which plants together) native Passiflora (passionflower) vines in the United States. Exquisite in bloom and great screening plants, these vines can mostly be found in the warmest parts of the country. There are two that can tolerate colder winter weather conditions and could be possibilities for your garden in Colorado. The hardiest native passionflower vines are Passiflora incarnata and P. lutea.

Boulder, Colorado is in the USDA plant hardiness zone 5b/6a so these plants will need to be located in a protected site, given lots of extra mulch to insulate the roots and will die down to the ground during the winter.  A plentiful amount of continuous snow cover is also an excellent insulating blanket for the winter.  If it is too risky to grow these two passionflower vines outdoors in Boulder, then consider planting them in large containers and moving the containers into a garage or basement for the winter.  Then move them out to the garden in late spring.

The native passionflowers are: Passiflora affinis (native to TX), Passiflora foetida (AZ, FL, HI, and TX), Passiflora incarnata (DE to MO) Hardiness zone 5-7 to 10. Passiflora lutea (PA to FL) Hardiness zone 5 to 9 and tolerant of winter temperatures down to -15 or -30 deg. C. Passiflora suberosa (TX), and Passiflora tenuiloba (NM to TX).

There are no worries about any Passiflora becoming invasive in Colorado. The areas where native or exotic passionflower vines are an invasive issue are locations such as Hawaii where there is not a winter freeze to control the plant. A good resource for invasive plant information is the Invasive Plant Atlas of the United States developed by the University of Georgia - Center for Invasive Species and Ecosystem Health and the National Parks Service (among other partners).