Cultivating Carnivorous Plants (2015)
RORIDULA
Roridula is a genus of proto-carnivorous plants that
has a mutualistic relationship with the two members of
the Pameridea genus, Pameridea roridulae and Pameridea
marlothii. Although each species in the genus Roridula has
sticky hairs like Drosera, neither produces digestive
enzymes. Instead, both rely on Pameridea, most often
Pameridea roridulae, to digest any prey that becomes caught
on their leaves and excrete nutrients. This mutualism
makes growing Roridula somewhat more difficult than
other carnivorous plants.
Both species of Roridula are commonly described as
woody shrubs, but large Roridula plants are more
accurately described as small pine trees with Drosera-style,
carnivorous needles. At maturity, Roridula dentata can
reach five feet (1.5 meters) tall. Roridula gorgonias is
smaller, only reaching 20 inches (50 cm) tall. Given
Roridula dentata’s immense size, it is not surprising that
occasionally a large plant will be spotted after having
snared a small bird.
The Fynbos of South Africa is the only place on
earth where Roridula can be found in the wild. Recently,
however, a fossilized member of the Roridulaceae family
was unearthed in Kaliningrad, Russia. This fossil,
preserved in amber, indicates that a very similar species
could be found all along the Baltic coastline 35 - 47
million years, when the region was a massive swamp.
Nowadays, both existent species live in this narrow
stretch of land along the Western Cape which
experiences cool, rainy winters and warm, dry summers.
Their native soil is, as with most carnivores, nutrient-
Roridula dentata with prey in cultivation at the
poor, and brush fires frequently clear the landscape.
University of Connecticut.
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Although most of the rain in the Fynbos falls
in winter, both species of Roridula grow year-round.
In cultivation, they produce flowers in mid-winter
or early-spring, which is shortly before the plant
sees a burst of spring growth. The flowers are large,
showy, and pink. Roridula must be pollinated in
order to set seed, although cross-pollination is not
necessary. Seed is hard and fire-resistant. In fact, a
simulated brush fire is useful for germinating the
seed of both species, although it is only strictly
necessary for Roridula dentata.
In Cultivation
Neither species of Roridula is easy to grow.
Both can experience fungal attacks as a
consequence of stress, and both will easily succumb
unless the proper conditions are maintained and the
fungal-infected
areas
amputated.
Fungicides,
insecticides, and fertilizers are all barely tolerated, if
at all, and can easily be more damaging to Roridula
than the underlying pest or problem.
With both species of Roridula, the easiest and
surest way to propagate them successfully is via
seed. It is rare to obtain a Roridula plant in any form
other than seed, probably because of the difficulty
in germinating the seeds. For both species, the
seeds must be kept moist--but not wet--after
planting. It will take one to three months for the
seeds to germinate. If they have not germinated by
the three month mark, simulating a brush fire by
burning leaf litter atop their pot may be useful.
After germination, the seedlings can be repotted,
but care must be taken to avoid breaking the roots.
It is possible to propagate Roridula via cuttings,
but it is difficult to do and, generally, generates
weaker plants than those grown from seed. Cuttings
should be placed in the same type of media mixture
as adult plants after being dipped in a rooting
hormone. After potting, cuttings should be given
high humidity, but not stale air (as would occur in a
sealed plastic bag). Bottom heating will increase
likelihood of rooting.
Neither species of Roridula can survive
Roridula dentata in cultivation.
stagnant, humid air for more than a few hours. As a
This plant is over five feet tall!
consequence, it is probably not feasible to grow
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CULTIVATING CARNIVOROUS PLANTS
either species in a terrarium due to the lack of fresh airflow. A mere few hours of stagnant, humid air can
result in the entire plant being overcome and succumbing to wilt and death.
Foliar fertilization can be of benefit to both species of Roridula, but it must be done carefully. A high
nitrogen, low phosphorous fertilizer, such as orchid fertilizer, is best, and should be lightly tested on a side
branch before the entire plant is dosed. An alternative to fertilization is to introduce Pameridea, but these can
be difficult to obtain.
Roridula dentata
The flower of Roridula dentata.38
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NATCH GREYES
Roridula dentata is native to the hot and arid inland South African mountains of Clanwilliam and Tulbagh
Ceres, centering on Cederberg. Plants are ordinarily found near streams and on moist slopes, which allow
them to access water via their deep taproots in times of little rain. The soils of these slopes are sandstone-
based, acidic with low levels of nutrients.
As
with
many
natives of the Finbos,
Roridula dentata is a
rapid grower, but it is
also a temperamental
grower. It will not do
well in conditions that
do not closely match
those of its native
habitat.
Unlike
Roridula
gorgonias, which typically
grows along a single
stalk, branching only
after flowering, Roridula
dentata grows as a true
bush, and sends off
multiple branches from
its central trunk. This
branching tendency is
good news for growers,
as it provides them with
more opportunity to
The flower of Roridula dentata just beginning to open.39
experiment
with
feeding and conditions. It is not infrequently the case that a plant will suddenly have branches that begin to
turn brown and die. The reason for this is mostly likely the result of humidity being too high, light being too
little, or too much prey being captured. In order to prevent loss of the plant, the affected area must be
amputated before the rot spreads to healthy sections of the plant.
The easiest way to propagate Roridula dentata is via seed. The most successful way to get the seed to
germinate is to scarify the seeds with sandpaper. Then plant the seeds, half covered, in an appropriate media.
A brush fire must then be simulated, or, at least, the chemicals released by a brush fire must be introduced
into the media. The easiest way to do this is to burn some twigs and leaves on top of the soil, trapping the
smoke in a glass jar and holding it over the seeds for several minutes. Alternatively, one can purchase a
smoke-impregnated seed primer and use that to simulate a brush fire.
After simulating a brush fire, the pot should be kept in full sun, and the soil kept moist. After
germination, seedlings of Roridula dentata will grow quickly, sending a single taproot deep into the soil. As a
consequence, Roridula dentata requires a large pot. Clay is preferable. As the plant grows, watering should taper
off to the point of not watering for several days at a time, as with Drosophyllum.
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CULTIVATING CARNIVOROUS PLANTS
Roridula gorgonias
Roridula gorgonias growing in cultivation at the Kew Botanical Gardens.40
Roridula gorgonias is native to the cool, humid area near the city of Hermanus, South Africa. As a
consequence, Roridula gorgonias prefers slightly cooler and wetter conditions than Roridula dentata. Perhaps the
easiest way to water Roridula gorgonias is via the tray method in summer, allowing the tray to dry completely
before filling with more water, but be careful not to overwater.
Unlike Roridula dentata, Roridula gorgonias does not require a simulated brush fire for its seed to germinate. A
simulated brush fire can, however, increase germination rates significantly. Growth of Roridula gorgonias is
slow, however, compared to Roridula dentata. This species grows at only half the rate of Roridula dentata.
My standard growing guide for Roridula is as follows:
✵
Media: A mixture of one part sphagnum peat and one part sand seems to work well.
✵
Moisture: Watering via the tray method and allowing the water to evaporate and stay evaporated for a
while between each watering is probably easiest. Roridula dentata should be kept drier than Roridula
gorgonias. Aim for as dry as Drosophyllum for Roridula dentata.
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✵
Humidity: Humidity should be kept low, and the air should not be allowed to become stagnant for
either species of Roridula.
✵
Pot Size: Pots should be made of clay, if possible, and around 1 gallon in size. Roridula dentata requires
a larger pot than Roridula gorgonias.
✵
Feeding: A high nitrogen, low phosphorous fertilizer diluted to quarter strength and applied to the
leaf may work, but should be tested on a small portion of the plant before being applied to the whole
plant.
✵
Temperature: Temperatures should be kept above freezing and below 95° F (35° C).
✵
Dormancy: Dormancy is not required for Roridula.
✵
Propagation: Roridula is most easily propagated through seed, but it can also be propagated through
leaf cuttings. The best method for propagating each species Roridula is discussed below.
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