Experiments with Highland Nepenthes Seedlings: A Summary of Measured
Robert Sacilotto • Botanique • http://www.pitcherplant.com/
Keywords: Ecology: Cultivation: Nepenthes.
One of the most difficult things to describe to someone is how to grow
a plant that is restricted in its tolerances. Partly to blame is our
human perception of these conditions. What exactly is “bright light”?
What is “clean water” and how acidic is “acid”?
Highland Nepenthes are often one of the more perplexing groups
to work with. What seems to work for one person fails when someone else
tries to reproduce the cultural environment. Nepenthes villosa,
for example, is not an easy plant to grow from seed; it has a narrow
range of conditions necessary to grow well. Beans are easy to grow, highland Nepenthes are
In order to get better insight into the needs of several species, I
conducted five years worth of experiments aimed at quantifying their
needs. Instead of subjective terms, I used tools to measure environmental
conditions in all test groups. A light meter, conductivity meter, pH
meter, recording thermometers and a high quality humidity meter were
employed to put some numbers behind the findings. (Cheap meters are dangerous
to rely on, so only meters that could be calibrated and tested were used.)
This way, anyone could nearly duplicate the conditions that were successful,
and avoid potential disaster by measuring variables before plants get
put into a bad environment.
The following Nepenthes were used in this study: N. burbidgeae, N.
edwardsiana (Tambuyukon type), N. fusca, N. stenophylla, N.
tentaculata (Mt. Tambuyukon type and Mt. Kinabalu type), and N.
villosa. All were raised from donated seed or very tiny seedlings
(cotyledon spread 0.63 cm., 0.25 inch). Dead or struggling plants were
considered indicators of exceeding the species tolerance to one or
more variables within their environment. The bane and beauty of using
seedlings is that they do not take long to indicate improper environments;
they die quickly!
Several points deserve mention, before getting into the “meat” of
this article. First, plants grow in a system, where the elements of culture
play off each other. For example, higher light levels require greater
nutrient levels, as plants need more nitrogen to eliminate photosynthetic
(waste) byproducts. Stresses from lower relative humidity might be offset
by lower light or more available moisture at the root zone. Thus, I am
not suggesting one rigid method, when explaining a successful technique.
My intention is to give benchmarks and warning signs.
Second, this article was written as a distillation from five years (1996-2001)
worth of records. A full description of these experiments would fill
several volumes of this newsletter with tedious detail. My intention
is to present a simplified summary of what happened during these experiments.
One example of this practical focus was to simplify the complex science
of light. The usual grower purchases a readily available light source
or uses sunlight. The intensity of the illumination striking the plants
is determined by the light source, the distance from the source to the
plants, and/or the amount of shading. The simplest way to get a reasonably
accurate measurement of intensity is to use a light meter, specifying
the unit of measure and the source (very important). For spectral analysis
of artificial lights used herein, contact the manufacturer.
Finally, it is important to note that, unlike formal experimental design,
there were no control groups, per se. In many of these species, seedling
death is the norm. Other growers, who worked with many of the same seed
lots, reported complete losses in difficult species like N.edwardsiana,
and N. villosa. Thus, it was nearly impossible to assign a control
group without first figuring out how to keep it alive! The main support
for these findings is that significantly large numbers of plants were
used. The results herein are preliminary and not conclusive; other factors
(such as bacterial infection, seed viability, genetics of the donated
seed, etc.) could have had an effect on these findings. Readers should
consider this article a detailed summary by a professional horticulturist,
rather than a classic, formal experiment. As far as I am aware, this
is the first time that meters have been used to quantify the major (growing)
environmental parameters, and that these measurements have been united
Seedling lots were from two hundred to four hundred seedlings per
species. The seedlings were carefully transplanted into groups of
32 per 10.2 cm (four inch) plastic pot at the cotyledon stage of
seedling development. Lesser quantities of seedlings were put into
the same size pots when I intended to expose these to extreme, probably
fatal conditions (such as pH below 4.5, or light below 4300 lx, i.e.
400 fc), or when the seedlings grew enough to need extra space. These “community
pots” were then placed into different, carefully monitored
environments (including different media). Groups were examined monthly
and compared visually. It was obvious which groups were prospering
and which were dead or growing poorly, so I did not measure each
Conductivity meter (American Marine, Inc., Pinpoint™ Conductivity
Meter) giving values in microsiemens/cm.
Light meter (Extech, model 40125), values were originally measured
in foot candles and converted to lux1.
Hygrometer/Thermometer (Extech model 44470), values given as relative
Min/Max thermometers (Taylor), temperatures were originally recorded
in degrees Fahrenheit.
Artificial light sources included:
High pressure sodium (Philips, SonAgro, 430W).
Metal halide (Philips, AgroSun™, MS400/HOR/AS, 400W).
A fluorescent combination using 50% Wide spectrum Gro-Lux® (Sylvania,
40W) plus 50% Interior Designer® cool white (Sylvania, 40W).
Greenhouse shading for sunlight was accomplished using Continental
Products® Koolray Easyoff. This horticultural liquid shading
was diluted/applied/removed as necessary to maintain fairly consistent
light levels. Artificial light sources were on for fourteen hours
per day (24 hour cycle). Unlike day length supplied by artificial
lighting, seasonal day length determined the photoperiod in groups
All plant groups used in this experiment were given identical preventative
fungicide treatment to discourage pathogens from degrading the test
groups. A mixture of Zyban® (4 ml/liter, 1 TBS/gal.) plus Subdue® (1.6
drops/liter, six drops/gal.) were lightly misted over seed or seedlings,
once every two months. Every other application, Cleary’s 3336® (4
ml/liter, 1 TBS/gal.) was substituted for the Zyban to reduce the
total chemical load. (Zyban® is the same as Cleary’s 3336® plus
Mancozeb®.) Nepenthes seedlings are subject to damp-off.
Usually, damp-off is caused by species of Pythium or Rhizoctonia. Botrytis and
several other fungi are usually less common as damp-off culprits.
Pathogen identity was primarily determined by examining conidia under
compound microscope. Non-systemic fungicides, such as Captan®,
were not used because they are less effective and the concentration
needed for pathogen control raised the conductivity of the soil to
deadly levels2. Mortality rate of untreated seedlings (two months
after germination) was between ten and eighty percent, so untreated
groups were not used in these experiments. Mortality rate of fungicide-treated
seedlings was generally below ten percent (two months after germination).
Twenty-four hours after fungicides were applied, all media were leached
with purified, aerated water, to remove soluble residues.
Another hidden seedling killer proved to be salts that slowly leached
out of perlite, one of the main media components. Perlite is hydrated
obsidian that is heat treated to expand. Perlite was added to purified
water (two parts water to one part perlite) and the conductivity
of the water increased more than threefold, over a two day period.
Since all examined groups of seedling Nepenthes seemed to
favor a conductivity level in the soil of between 10-20 microsiemens;
the perlite was pushing the conductive load of the media to dangerous
levels (24-75 microsiemens). However, after repeated leaching the
perlite became a great, inert material to use in seedling media mixes.
Certainly, the quality of perlite is variable.
The irrigation water was purified by reverse osmosis and aerated
using a utility pump. The conductivity of the water was 10-12 microsiemens.
Eighty percent of all groups were watered twice a month with a boiled,
strained, peat moss and sphagnum water extract (tea) which was added
to irrigation water prior to aeration. The formula, pH and conductivity
levels of this diluted tea were monitored and standardized for the
tests. The tea was used to add nutrients, regulate soil pH and examine
the effects of conductivity in an organic, acid matrix (media containing
primarily tannic, fulvic and humic acids as acidifying agents). Conductivity
values given here are from water extracts of potting media. Water
extracts from the media were made by saturating the media for one
hour and passing purified water (approximately equal to the soil
volume) through the media. This leachate was measured for pH and
conductivity. As one might expect, the makeup of water ultimately
determined the conductivity of the media. The breakdown and leaching
of organic materials in the media did not elevate conductivity significantly,
i.e. organic compounds tend to yield low conductivity products as
they leach or decompose. It may be helpful for readers to imagine
a hydroponic model, where the water chemistry has more effect on
soil chemistry than the media. This is especially true in media consisting
largely of perlite. It is also important to note that the effects
of conductivity relate to pH in terms of seedling tolerance; if the
pH of the media is outside a plant’s preferred range, higher
conductivity values tend to make the stress worse (higher death rates).
When “optimal” conductivity values are given, these are
what appeared optimal at suitable pH.
All right, before this sounds too much like a physical science treatise...on
to the plants!
Results on specific plants
N. burbidgeae was fairly broad in its tolerances,
especially in regards to soil types and temperature. This species
tolerated every media blend used. Stunted growth was evident with
50% silica gel, 10% peat moss chunks, and 20% each sphagnum and fir
bark. The best growth rates were in media consisting of 50% perlite
(leached), 10% peat moss chunks, 10% fir bark and 30% sphagnum moss
(dead, long fiber). Media with no fir bark and higher percentages
of sphagnum worked equally well. Plants tolerated temperature in
the range of 9-41°C (48°-105°F), but grew about 50% slower,
with fewer pitchers, when night temperatures were consistently over
(65°F). The best growth occurred when temperatures were 20-29°C
(68°-85°F) during the day, and 12-16°C (54°-60°F)
at night. Optimal pH was 4.8-5.5. (Slower growth was observed at
a pH of 3.5.) Optimal conductivity was 10-24 microsiemens; foliar
burn appeared after prolonged exposure (one week or more) to levels
above 60 microsiemens. Relative humidity seemed best within the range
of 68-95%. Constant high humidity (over 90%) encouraged disease outbreaks
and higher death rates, especially in seedlings less than one year
old. Preferred light levels were 7000-9700 lx (650-900 fc) under
high pressure sodium, 6500-9100 lx (600-850 fc) under metal halide,
5400-7300 lx (500-680 fc) under the fluorescent combination, and
8100-11000 lx (750-1000 fc) under sunlight. Plants survived lower
light levels, but poor pigmentation and etiolated growth was observed.
Plants responded well to dilute Miracid® fertilizer , applied
monthly to the pitchers3. Light misting (foliar feed)
of the same solution, monthly, had no noticeable effect on the plants.
N. edwardsiana was, without question, the most fragile seedling
observed, although the plants became much sturdier as they aged.
The following conditions were concurrent with 100% mortality in cotyledon
stage seedlings: constant high humidity (over 90% RH), water droplets
sitting on leaves or crown, conductivity over 45 microsiemens, and
pH above 6. This test group was the smallest (after two months),
but a few plants were growing gloriously well in 50% perlite, 10%
peat moss chunks, 10% fir bark and 30% sphagnum. In addition, a top
dressing of live sphagnum proved very helpful; many of the roots
weaved through this layer. Optimal soil conditions appeared to include
a pH between 4.8-5.4, and conductivity at levels below 24 microsiemens.
Humidity appeared best between 65-85 RH, although older plants (one
year or greater) tolerated brief (1-3 days) exposures to 90-99% RH.
Under high pressure sodium, light at 7500-9100 lx (700-850 fc) seemed
optimal. Other light sources were not tested. Due to the fragile/valuable
nature of the few plants, only insects were fed to the plants. When
the pitchers were about 3 mm (1/8 in.), dried fruit fly (Drosophila
melanogaster) larvae were used as food. As the pitchers grew,
ants (Acanthomyops sp.) were used as food. Plants grew most
vigorously when night temperatures were 13-16°C (55-60°F)
and day temperatures ran 21-29°C (70-85°F). Growth was very
slow for the first 8 months; as the plants reached 2 cm (3/4 inch)
in diameter, the growth rate went up dramatically.
N. fusca proved to be very tolerant of cultural variances.
None of the test groups showed greater than 25% death rates, except
seedlings raised without fungicides, which had from 10% to 100% death
rate. This death rate appeared to be random. Although the seedlings
survived all the cultivation conditions I subjected them to, some
patterns indicating preferences did occur. Media containing higher
organic components performed better, i.e. 30% perlite, 10% peat moss
chunks and 60% any combination of sphagnum and/or fir bark. A slightly
more acidic condition was preferred, from 4.5-5.0 pH. Conductivity
tolerances showed good growth between 10-45 microsiemens. Humidity
was optimal from 65-90% RH. Though the seedlings tolerated from 10-38°C
(50-100°F), growth and pitcher production was poor when nights
were routinely over 21°C (70°F). Lighting experiments yielded
the following: metal halide, high pressure sodium and sunlight all
performed best from 6400-8600 lx (600-800 fc). However, the most
vibrant colors were obviously in plants grown under 50% Gro-Lux® and
50% cool white fluorescent at 5400-7500 lx (500-700 fc). Some plants
grown for several months under sun, metal halide or hp sodium were
moved to the above fluorescent combination with dramatic results;
green leaves turned bronzy, light reds became vibrant magenta and
spotting on the pitchers became much darker. Growth rates, under
all light sources, were similar. Miracid® at 1/4 strength3, applied
inside pitchers, was effective. Ants worked as well for feeding.
N. stenophylla was the slowest overall performer, and I am
not certain I ever found ideal conditions for growing it. Generally,
the plants grew reasonably well but very slowly, although about 10%
of the plants, within a group, tended to grow faster than the others.
Despite the sluggish growth, the plants appeared healthy. Pitcher
feeding seemed very important, but not all plants responded similarly;
about 30% of a group grew 200% in six months, whereas the rest of
the seedlings grew about 20% in six months. Miracid®3, Drosophila larvae
and ants were equally effective in feeding tests. Despite somewhat
ambiguous results, plants grew reasonably well in media containing
40-50% perlite and 40-50% sphagnum moss; adding about 10% fir bark
had no noticeable effect. Conductivity was best near 10-22 microsiemens;
stress appeared at levels over 45 microsiemens. The pH observations
were inconclusive. One plant (in a container with 5 other similar
seedlings) took off at pH 4.0 , while the rest appeared impaired.
Most plants grew reasonably well at a pH of 5.0. All light sources
worked well, but the best observed growth was under sunlight at 8600-12,000
lx (800-1,100 fc). Plants seem to resent water on the foliage and
crown, when young; nearly 30% died if their tops were wetted routinely.
Plants grew well at 65-90% RH and tolerated temperatures of 10-38°C
(50-100°F). Best growth was achieved with nights at 13-17°C
(55-62°F) and day temperatures of 24-29°C (75-85°F).
Worth noting, the gradual appearance of mosses on the media surface
appears to coincide with increased growth rate/plant health.
N. tentaculata from Tambuyukon and from Mt. Kinabalu behave
like two different species. Though I am trusting the accuracy of
the donors, the morphology of the plants supports the original, supposed
ranges. Both types showed an affinity for acidic media, pH 3.8-5.0.
In several cases, plants growing near a pH of 4.0 did better than
those at higher pH. This was observed in seedlings of Tambuyukon
origin; Kinabalu type plants performed fairly equally from pH 3.8-5.0.
Peat tea was found more useful in maintaining a lower pH and overall
health in Tambuyukon plants. Both groups tolerated conductivity ranges
from 10-40 microsiemens. A media of 30% perlite with 20% peat moss
chunks and 50% sphagnum worked well for both types. Since these plants
showed affinity to low pH, a few of each type were potted in pure
peat moss, which had the dustier fraction removed. Despite early
success, all plants grown in pure peat were dead after one year,
whereas plants in better aerated media survived. As temperature ranges
were increased, the differences in Tambuyukon and Kinabalu plants
became dramatic. Kinabalu plants were much more tolerant of higher
temperatures (10-37°C, 50-98°F). The Tambuyukon plants started
dying when either the day temperature went much beyond 29°C (85°F)
or the night temperatures stayed above 18°C (65°F). Whereas
other species usually showed stress signs before dying, N. tentaculata from
Tambuyukon often died overnight, with little or no warning. I could
not help but be reminded of how Darlingtonia suddenly collapses
after persistent warm media. Evident, as well, was a relationship
between light and temperatures: the higher the temperature, the lower
the light tolerance in N. tentaculata from Tambuyukon. Both
races grew well under 6500 lx (600 fc) of the previously mentioned
fluorescent light mix. Under high pressure sodium, 5400 lx (500 fc)
was effective. Tambuyukon plants did poorly, but survived under metal
halide (no optimal range observed), whereas Kinabalu types thrived
at 6500-7500 lx (600-700 fc) of metal halide. Both types did well
receiving from 6500-9100 lx (600-850 fc) of diffused natural light.
Under the above light levels, Kinabalu plants thrived from 14-32°C
(58-90°F); Tambuyukon plants did best from 10-26°C (50-78°F).
In this study, N. tentaculata from Tambuyukon was the most
sensitive species to high temperature, even more sensitive than N.villosa.
It may be that the dark green leaves are subject to high heat gain,
or that symbiotic relationships, especially at the root zone, are
greatly influenced by temperature. Chelated iron availability may
also be critical, as distressed plants showed foliar symptoms similar
to iron deficiency. More study on this species is needed.
N. villosa had some unusual preferences in culture. For a
cloud forest dweller, this species showed a high death rate when
seedlings were misted or kept at very high humidity (> 90% RH)
for long periods (a week or more). Optimum humidity levels were 65-85%
RH. Though the plants tolerated warm nights to 24°C (75°F),
the plants stopped growing well when nights were above 17°C (62°F).
Many seedlings stayed the same size for over one year, when constantly
exposed to nights between 17-24°C (62-75°F); most of the
plants in this group ultimately died. The best plants were grown
with night temperatures near 14°C (58°F) and day temperatures
from 21-29°C (70-85°F). N. villosa proved very sensitive
to conductive water or media, needing a range below 25 microsiemens
to grow well. Seedlings exposed to foliar Miracid® at 1/4 strength3
and 1/6 strength3 died within two weeks. Seedlings 3/4 inch or more
in diameter, however, responded well to the above solutions when
placed only in half (some) of the pitchers. Ants proved to be effective,
as did dried Drosophila larvae. Because of the low nutrient
level of the media, pitcher feeding appeared critical for plant health.
Since the tiny seedlings make pitchers too small to feed with insects
(practically speaking), I developed a technique to deliver the dilute
Miracid® into pitchers 3mm (1/8 inch) tall, or less. Hair, from
Whitetail deer (Odocoileus virginianus), was clipped to 3mm
(1/8 inch) and soaked in the fertilizer. Since deer hair is porous
in all directions, it proved an effective carrier for the nutrients.
One or two hairs could easily be put into a tiny pitcher, once the
pitcher lid was removed. Of the seedlings given this treatment, 75%
showed significant growth rate increase. However, the other 25% usually
died. When media with significantly higher organic/nutrient levels
were used, the plants died. Often the low nutrient uptake of the
seedlings created an ideal environment for blue-green algae to form
a pellicle on the media surface. Aside from possible phytotoxic compounds,
this pellicle decreased oxygen supply to the roots. In every test
lot, N.villosa displayed an affinity for extremely
well oxygenated media, or media with very high porosity. The best
plants were raised in 75-80% perlite, with the remaining fraction
sphagnum and peat moss chunks. Peat tea was used periodically to
maintain a pH of 4.8-5.0 and a conductivity of 10-18 microsiemens.
Plants given media at pH 3.8-4.0, (conductivity 28-41 microsiemens)
were stunted. A thin top dressing of live sphagnum seemed to help,
but was not as useful as in N. edwardsiana culture; the N.
villosa did not root (much) directly into the live moss.
Although other growers have been successful using metal halide as
artificial lighting, I was not able to get satisfactory growth with
ranges of 8100-12000 lx (750-1100 fc). Much better growth was achieved
using natural sunlight 8600-11000 lx (800-1000 fc), the fluorescent
light combination mentioned earlier 7300-8100 lx (680-750 fc), and
high pressure sodium 8400-9700 lx (780-900 fc). When a single fluorescent
(2-40 watt bulbs, as described earlier) was angled to add to the
high pressure sodium spectrum, colors and general plant health was
improved. This is interesting, since the fluorescent lights only
added about 900 lx (80 fc), when used in this fashion. Plants growing
under the high pressure sodium/fluorescent combination grew faster
and produced more pitchers.
Shortly after this study was completed, Dr. Perry Malouf (personal
communication4) did some limited soil analysis on Mt. Kinabalu, examining
samples from near the root zones of several Nepenthes species.
His preliminary findings on conductivity and pH in the field were
very similar to those found to be near optimal in these seedling
experiments. In general, Nepenthes seem to favor a soil pH
near 5 with very low conductivity.
It is hoped that this information will help growers achieve success
in their efforts and that ecologists can use the quantified data
such as acid tolerances and conductivity to better predict when a Nepenthes habitat
is threatened by factors such as acid rain, fertilizer runoff or
deforestation. Acid rain can have a pH less than 3, and I have measured
conductivities of over 70 microsiemens in Virginia’s polluted
rainwater. I am concerned that the increased use of high sulfur coal,
as fuel in China and surrounding countries, will introduce acid rain
to highland habitats. The reckless disregard for pollution, that
has killed fish and most of the high elevation spruce forests in
Virginia, could manifest itself in places like Mt. Kinabalu and Mt.
Tambuyukon, transforming the currently vibrant ecosystems into ecologically
damaged mountainsides. With the rapid development of the Eastern
hemisphere, I fear many of us will live to witness such a tragedy.
Monitoring rain water quality in montane habitats may prove vital
in preventing habitat destruction by an invisible threat. Minimizing
the risks is key to avoiding loss of species diversity.
1. Values given in lux can be converted to foot candles using 1
lx = 0.0929 fc.
2. My thanks to Dr. Jay Stipes, VA Polytechnic Institute, for assisting
me in finding an effective fungicide combination.
3. Miracid®, when used, was usually applied at 1/4 the labeled
strength for house plants, 0.3 ml/liter approximately equals 0.2g/liter
(1/4 tsp/gal. approximately equals 0.75g/gal.). Purified water was
used. The solution was put in each opened pitcher, filling the pitchers
to the top (peristome).
4. Dr. Perry Malouf can be reached via e-mail @jhuapl.edu.
Figure 1: Tiny Nepenthes villosa seedlings being manipulated
with a pair of forceps.