Phaseolus caracalla: Imposter Amongst Us but Beautiful All the Same
Phaseolus
caracalla, is a typically a tender perennial vine, native
to South America, and hardy to Zone 8 to 11. P. caracalla can tolerate
some frost exposure but extended periods will result in the plant dying back to
the roots. This can be countered by planting it in a sheltered sunny location
or treating the plant as an annual, more on that in a bit. In my own garden
this plant typically dies back to a woody base and sends out annually 10 feet
of growth. Such growth makes it excellent for covering up unsightly walls or
the view of the neighbor’s lawn gnomes. Like many other vines training of
growth is crucial in keeping a tight tidy appearance. As with many vines growing
on walls we want them to remain 2D not 3D, bulging away from the wall, as such
any growth reaching outwards should be removed. The growth is easy to train as
it is not woody at all, use a trellis or a fish wire setup as your support
system, as this vine climbs in the same manner as clematis weaving its growth
tips and then wrapping around a support. This plant is very tolerant of poor
conditions. It has found residents in a long bed, that has probably the worst
soil in the whole garden. The soil in this bed is hard compacted sandy loam,
and drains quickly, being in a constant state of drought. Despite this, the
vine has not once shown any signs of stress other than pale green leaves at the
end of the season. A benefit of having this vine and in fact any legume is that
they are nitrogen fixers, absorbing and converting atmospheric nitrogen to
usable nitrogen via a fungal/ bacterial relationship in their roots, thus
feeding the soil. It is this adaptation that allows not only P. caracalla
but Legumes as whole to thrive in harshest of environments.
The
flowers of this species resemble the classic legume flower but are slightly
corkscrewed in shape, hence the common names of corkscrew or snail vine.
Unusual among flowers in that the blooms are asymmetrical in shape. Several
studies have revealed that this species uses a suite of large body bees, Bombus
and Xylocopa sp., as pollinators (). This seems to be true in my own
garden as members of both genera have been seen on this plant. Ants as well
have soon a particular interest in the flowers. The flowers of this species are
a pale purple and bear no scent. These flowers give rise to pods that resemble
that of sword peas, being narrow and long. Pods split off and seeds are spread
by the wind. In my own garden there have been a few volunteers, and it should
be noted that in more tropical regions this plant has been noted as a pest. As
such it is best to check your local agricultural department to see if its
listed. Seedlings are easy to remove while young and can be potted up and
shared with ease.
This plant can be
propagated vie two methods. The first is by cuttings. Cuttings can be done by
cutting a section of branch and depending on how many new plants one wants, a
gardener can either do cuttings consisting of 4 to 6 inches or using a single
node. Using a single node can be done two ways, one involves removing one leaf
and then placing the bare side on the soil and allowing it to root. The other
involves laying the plant flat and on both leaf axils roots should emerge. With
both methods make sure to peg your plant down. You can use a paper clip and
bend it into the shape of an arc to ensure cuttings are in contact with soil.
The second method is by seed. Finding seed online is a bit difficult, as we shall
discuss n a bit, but if found sow the seed and lightly cover providing heat if
possible. Like many tropical vines, if the young seedling experience cold
weather they may turn yellow. Seedlings
can then be planted out after the last frost.
The Taxonomic Mess and How the Gardener Can Sort
It Out
Finding
information let alone buying this vine can be a bit of a hassle. Another vine,
closely related, and resembling it exist, its name being Vigna caracalla.
V. caracalla gets all the attention, outshining its relative. Featuring
a similar growing habit to P. caracalla, differences arise with the more admirable blooms of the latter.
Blooms on this plant are corkscrewed but to greater extent. Flowers are white
with some purple blush and a yellow interior. Along with that this species has
a stronger scent then its purple relative. Sounds great! No wonder these plants
more popular! While not all is perfect in paradise. Vigna caracalla is
more frost tender and requires a lot more protection to survive winter, along
with preferring a richer soil.
Trying
to find a reliable source for either plant is difficult to say the least and
that is due to naming. Both plants have had several name changes. Troubling,
these changes have mostly consisted of the two species changing names or at
times even sharing the same name! Perhaps
the reason as to why there is so much confusion is due to how so many of us
gardeners come across this plant. When I had first stumbled upon this jewel it
was at a big box store in spring. It was being sold as Vigna caracalla yet
when it first bloomed, then did it reveal its true identity. My best advice when buying this plant is first find a reliable
source if you’re shopping online, and second in person look at the blooms. P.
caracalla has more open flowers that are purple throughout and V. caracalla
has flowers that are mostly white. Regardless both plants are worthy of
garden space.
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