Purple Passion Vine, Is it right for you?

I first saw passion vine when I was growing up in Southern California.  It was a woody vine covering a fence in my Grandmother's back yard.  It was probably blue crown passionflower, Passiflora caerulea, a native of South America. The flowers reminded me of flying saucers, perhaps from 'Lost in Space' in the 1960's.   Ever since then I have been drawn to having some of my own.  

The flowers of purple passion vine are beautiful and have
a pleasant sweet scent.  It's native to the Southeastern US to
Southern Virginia.  Winter hardy to USDA zone 5 (5-9).

There are over 500 species of passionflowers worldwide.  About 15 species are native to the continental US. Only two are found growing naturally from Virginia northward, purple passionflower and yellow passionflower (Passiflora incarnata and P. lutea, respectively).  Purple passionflower is the showier of the two and the most cold hardy, surviving as far north as USDA zone 5, but more common in zone 7a and warmer.  It will die back to the ground in zones 8 and colder.  In my zone 6b landscape it dies back to the ground each fall by comes back strongly and by mid-July when it starts to climb over neighboring shrubs. 

Variegated fritillary, Euptoieta claudia, is one of the butterfly species
that uses purple passion vine as a larval host.

Purple and yellow passionflowers are the larval host plants for the gulf fritillary butterfly (Dione vanillae).  This is primarily a southern species of butterfly.  Not surprisingly the  natural range of the gulf fritillary roughly corresponds to that of the purple passionflower.  Other butterflies common to the Mid-Atlantic region that utilize purple passionflower are the pearly crescent and variegated fritillary.  There are a variety of insects that feed on the leaves and fruits including Japanese beetles, grasshoppers and katydids. I have observed some spotted lantern flies on the vines but not to the extent that they feed on Virginia creeper or grapes.

In addition to the beautiful and fragrant flowers purple passion vine also produces edible fruits.  The structure of the fruits is similar to a pomegranate, with a sweet-tart gel surrounding a small hard seed.  The flavor is similar to guava with citrus and floral notes.  It can be eaten raw by sucking the pulp off the seeds or used to make jellies or syrup.  I prepared a syrup with sugar, water and pulp that could be used to add a 'tropical' note to mixed drinks.  Other names  for purple passionflower include Maypop and Liane de Grenade.  These are in reference to the noise that the fruits make when stepped on and popped.  Fruits ripen 8 or more weeks after pollination (mid-July to Mid-September, here).  They are fully ripe when slightly wrinkly and ready to fall off the vine.  

These fruits are not fully ripe yet, a little more tart than sweet,
but still good for making syrup. A ripe fruit would be a
little wrinkly and easy to pluck off the vine.

 

I bought a single plant in the fall of 2013.  Each year it got a little bigger.  After 6 or 7 years it was popping up in the lawn about 5 yards from the initial location.  It took nearly that long before the first fruits appeared.  The reason for this is that  purple passion vine  is not self-compatible, i.e. it does not self fertilize easily.  There are several mechanisms it employs to prevent self-fertilization.  One is biochemical, where pollen is inhibited from growing if it lands on a stigma of the same plant (a plant with the same genetic makeup).  There are also a couple of 'mechanical' means to discourage self-pollination.  

Here in mid-August the vine is growing over and shading
the asters and goldenrods.  In addition to the flowers,
passion vine can be recognized by its deeply cut
trilobed leaves and long tendrils.

Here you can see the separate male and female flower parts.  This photo was
taken in the afternoon after the stigmas have dropped.  The nectaries
attract large bees that walk in a circle around the pistil,
picking up and depositing pollen in the process.

One mechanism involves physical separation of male and female parts within a single flower.  When flowers open in the morning the female stigmas are held upright, while the male anthers, bearing pollen are facing downwards, hovering over the nectaries.  Flowers are exquisitely designed so that larger bees, especially the eastern carpenter bee, gathers pollen on its back as crawls over the nectaries.  Later in the day the stigmas drop down over the nectaries to pick up pollen from bees that had visited other flowers earlier in the day.  You can find more detailed photos of the flower at this post from Botany Nerd.  Another mechanism is that there is only one open flower at a time on a given stem.   Since that flower can't self pollinate, cross-pollination is the only option.  For detailed information  on how purple passion vine grows check out this article by Christopher M. McGuire in Economic Botany.

Even though all of the sprouts I have are from a single parent, it is now large enough to produce sufficient stems so that there is ripe pollen from distant stems finds its way to a receptive stigma.  This fall I got over a gallon of fruits from this single parent.  I imagine the yield would have been much higher if there were multiple parent plants around.

These are the vines that I pulled down at the beginning of October
with the jug of fruits that I pulled off.  It generally takes 8 weeks
for the fruit to mature, so these were probably 1-2 weeks too soon.

As noted above purple passion vine can be very aggressive.  The vines, growing up to 30', are supported by tendrils.  These tendrils are weaker and less permanent that those of wild grapes but they are still a nuisance when trying to bring a vine under control.  These vines can shade out supporting shrubs and block the view to other elements in your landscape.  

For this reason I would not recommend purple passion vine for smaller gardens or in gardens where plantings are well defined.  It is suitable for large spaces that can tolerate an aggressive vine that can cover the details.  Some suggest growing it in pots where the roots can be contained.  I have not tried that, but it does seem like a reasonable solution for this spreading vine.  I have found that I can control the spread with glyphosate, either normal foliar spray or by treating the cut stems with 20% glyphosate.  Next year I will make an attempt to contain the spread by treating shoots that come up outside the desired zone.  This approach has worked to stop the spread of new vines into the surround lawn areas; actually setting the reemergence back by more than a year.

I am a little concerned that this vine could escape and become a nuisance weed, considering that I am outside its native range (though only a few hundred miles).  I am somewhat comforted by its sensitivity to frost, where underground buds need to remain above freezing to survive.  A random seedling is not likely to survive its first winter.  Native Americans were known to use the vine medicinally and as food as far north as Virginia,  That it hasn't moved further north in the last 500 years is comforting.   Also there are a number of common insects that feed on the plant so there are biological controls in place.  

So the question remains, is this a good plant to introduce to your landscape?  As is often the case the answer is... it depends.  Among the positives are it has beautiful, fragrant flowers, it supports a variety of native insects, it has edible fruits, it dies back in winter in cooler climates and does little physical damage to supporting plants. (It does however persist as a woody vine in climates warmer than zone 8).  On the negative side it's an aggressive grower that can shade out other plants, and obscure their form, it's not compatible with a formal landscape, it is attractive to native carpenter bees (+/-) and the wide spreading rhizomes that can sprout up in random locations.  

Overall for me it brings more joy than it does frustration.  I think my joy can be increased with just a little more management early in the season.