Grow Guide
On the cultivation of Nepenthes
First it should be stated that this guide is based primarily on the work of Xavier Garreau de Loubresse of Select Plants. I highly recommend anyone interested in proper cultivation to read his 2012 paper on the cultivation of Paphiopedilum, the genus of orchids that often occur in the same habitats as Nepenthes and whose cultivation is nearly the same as the genus of interest here. Due to this change of understanding of what carnivorous plants need I decided it was time to rewrite this guide and provide an explanation of some concepts that cause frequent misunderstanding and a jumping off point for those wishing to grow their plants faster and better. There is a lot of myths around the requirements of Nepenthes as well, some insight on these is provided and why they came to be. My hope is that this helps other growers grow better plants and stay in the hobby rather than giving up on seemingly slow plants.
Basics
In orchids it is increasingly understood that fertilization is required for proper growth and therefore that community is slightly more receptive towards the idea. However, carnivorous plants has had a long history of growers saying “Don’t fertilize your plants” and sadly this concept has frozen the progress of growers of Nepenthes amongst the other genera. Overall though, the other carnivorous plants are less demanding in their nutritional needs and have less issues reaching maturity, except for certain species and genera like Darlingtonia. It should be alarming for any grower that a vine that grows faster than the surrounding foliage and trees in the wild grows at snail’s pace in cultivation. Similarly, photos of healthy wild Nepenthes are extremely impressive in stature with a lush green color – hard to believe for a plant that tries to rot constantly in cultivation. Something is clearly wrong with what we are doing in cultivation.
Frequently cited as the answer to bad growth is incorrect temperature, water on the leaves or too much water, random fungus that nobody ever identifies, or light. Reading the replies to questions from new growers wondering what is going wrong is incredibly boring after a point. Apparently, it was missed that Nepenthes grow in a practical rainforest. According to the status quo: the rain comes only in the morning and the rain goes around the leaves so they don’t get wet; fungus is also not a specific identified pathogen like glomerella but instead is a monolithic entity that is all and any issue afflicting Nepenthes; and the cure for any disease, thrips, mites, or cancer is Bayer 3-in-1. This is of course ludicrous. The temperature is slightly more interesting since it affects the plants metabolism and therefore the plants nutrient requirements fluctuate according with the temperature range, a concept often lost. Many growers who have tried growing in freezers realize that many Nepenthes slow down dramatically when given cold temperatures, this is simply because the cold temps slow the plant’s growth down and therefore nutrients in the soil can sort of “catch up” to the growth rate and the plant visibly becomes greener. Apparently, temperature is probably critical for rooting or flowering; however for average growing, hitting a certain temperature is not critical.
Similarly, the sunburn issue is a bit aggravating. Many growers like the red leaf coloration of species like N. peltata without ever realizing most peltata have perfectly green leaves in the wild. It should be noted too that peltata is one of the most painstakingly slow species in cultivation, and it should be no surprise that most grower’s slowest plants also have red leaves. This fertilizer issue is often “improved” by reducing light and therefore photosynthesis – this lowers the plant’s nutrient demand and therefore new leaves green up. Using a high nitrogen fertilizer can actually momentarily speed up the plant’s metabolism (the effects are not always visible as in new leaves) but then this stretches the plant’s resources of other nutrients, worsening the red.
As these statements have mentioned nutrition being the root cause of most issues of these plants it is a good idea to clarify on this concept that Nepenthes need nutrients, which despite being very clearly carnivorous is a lost concept. Nepenthes are plants and therefore abide by the rules of plants, mainly they require certain nutrients in order to live and photosynthesis - without these nutrients they die. Due to their carnivory it seems a lot of people think they actually “eat” like animals do, which while they can absorb aminos, is not the purpose of their carnivory. From their prey they obtain 2 nutrients typically low (not devoid) in their environment, Nitrogen and Phosphorous. This is interesting because it means the pitchers are not that great at absorbing other nutrients other than these two, and while they can absorb Magnesium etc via the pitchers it is inefficient and therefore pitcher fertilizing is a bit flawed although can be helpful and certainly better than not fertilizing.
It is often said that Nepenthes grow in nutrient devoid areas. This is simply not true and with zero evidence. It is extremely difficult to find anything free of ionic nutrients, even supposedly inert medias like rockwool or LECA. Ultramafic soils like on Kinabalu are extremely rich in nutrients, hence the name “ultra mafic.” A large quantity of these nutrients are available to the plants especially Magnesium and Nickel. There is not much denying of this since studies on these soils show the nutrients are freely available, and second, Nepenthes are well documented as growing directly in this strange substrate so no excuse of growing in less nutrient filled moss is applicable. The ideal available soil Magnesium level for vegetables is around 60 ppm (mg per kg) while soils on Kinabalu contain around 800 ppm! The next argument is that the Nepenthes simply don’t absorb these nutrients which is also absurd as fertilizer responses are known in this genera, and also a leaf analysis on Nepenthes shows a Magnesium level of 0.4% which is 4,000 ppm! Furthermore, this accumulating of nutrients in plants in higher quantities than the substrate is true of all plants, which only makes one wonder if plant derived substrates like coco coir or Sphagnum are actually nutrient devoid as so often touted. This all points to the fact that fertilizing Nepenthes was improperly done to start with and as a result it was better not to actively fertilize but instead rely on the growing media to provide a slow release of nutrients to the plant. This safety precaution (as not to make a mistake fertilizing) has blinded many into making this applies to what nature does effortlessly rather than try to experiment and figure out what the nutrient needs of Nepenthes are.
Substrates
Nepenthes like all plants need a substrate. We cannot obtain and use ultramafic rocks or the strange moss (not sphagnum!) that epiphytic species grow on in situ, so we must make a good substitute. Most often used is Sphagnum, typically the New Zealand variety, and while it can be used and has been so many times with great success, I consider it the worst choice. Its high saturation slows down rooting success at cuttings, imports from nurseries like BE stunt in it (BE’s Neps are acclimated to growing in coco), and root growth is often pathetic. The short lifespan of the substrate also makes it impossible to use while fertilizing (repotting must be every 6 months if fertilized ideally), which speeds up decomposition and untangling the strands while repotting is impossible without breaking many roots. Certainly, it can be used, but it is not efficient or affordable with many plants.
The other media that is increasingly used is coconut coir. This substrate is now more accepted as a growing media but took a while to catch on and many are still skeptical of it. This is surprising considering a few large growers use it with great success, Borneo Exotics uses it exclusively and has so since they started. It seems that the high EC value (i.e., TDS meters convert EC into an approximate and inaccurate ppm) scares a lot of growers from using it, and even when they do use it, it is only after repeated soaks of water to leach salts out of the coir. Ironically, few carnivorous plant growers actually know what these salts are that cause coir to have a high EC. A quick search reveals that the nutrient composition of coir is no great mystery since it is well documented in hydroponics as well as orchids. The “salts” in question are Sodium and Potassium, mainly because the coconuts are from saline environments (Sri Lanka being one of the biggest exporters of coir) and also since the coconuts are sprayed with Potassium chloride, the main Potassium fertilizer used in agriculture. As thoroughly explained by Xavier, one of the main issues with coir is that what started as a good byproduct of the coconut industry was then cheapened to allow easier production by using green coconut husks rather than mature brown coconuts. This is essentially like expecting a green sapling to make as good a house as mature lumber. The result is a product that breaks down quickly and leaches a brown “coconut tea” constantly that can inhibit plant growth if not watered heavily. Furthermore, the husks are rinsed using the rivers in Sri Lanka, creating an ecological disaster of stained brown polluted rivers, hardly the eco-friendly alternative to peat that it is so often promoted as.
It should be noted that coir does make a good media for Nepenthes, arguably superior and cheaper than Sphagnum. The issue of the excess Sodium is concerning however since it can interfere with fertilizing and also is slowly released over months. While most Nepenthes growers soak and flush coir to get rid of these nutrients, such a process only gets rid of about half of the K and Sodium since the rest is tightly bound to the coir. The solution to this was a procedure created by Xavier that is very similar to how a water softener works but in reverse. The coir is soaked in a solution of Magnesium sulfate (Epsoms salts) and Calcium nitrate or other Calcium fertilizer (I would recommend Calcium sulfate since Ca nitrate stunts Nepenthes) so the ions swap and replace a greater proportion of the more dangerous Sodium. Then the coir is flushed and rinsed like normal. BE chose to heat sterilize their coir by boiling or steaming batches, something difficult for most to do and probably breaks down the coir faster – however it does accomplish a similar effect and can semi sterilize the media. It should be noted that coir is rarely used in the orchid world and when it is used it typically ends in sickly plants after a promising start. The promising start is due to the coirs hormone content (it is the husk of a seed after all) that stimulates root growth and afterwards runs out. The increased success with Nepenthes is interesting considering this and perhaps points to Nepenthes tolerating high concentrations of Sodium, this would make sense because N. viridis, sumatrana, and treubiana all make their homes on cliffs and bluffs directly on the sea, with even N. merriliana sometimes found growing in brackish mangroves. For most growers, doing this complex rinsing process is probably too complicated and time consuming, but so far rinsing before potting with pure water is successful.
Kanuma and akadama are two similar products mined from Japanese mountains meant for bonsai. As a Nepenthes substrate they have a lot of good qualities, the small size is best used and comes off the roots easily when repotting causing minimal damage. When used alone it has an excellent growth effect on many Nepenthes such as hamata, ham x ed, palawanensis, most Philippine species, etc. With some appropriate fertilization it can be made to work well on the rest of the genera as well such as stenophylla, rein etc. Even cuttings root surprisingly well and quickly in it despite it seeming not to make good contact with the stem. Sadly, both products are increasingly expensive, and this makes it very prohibitive to use on any scale. They do work though; it is important to rinse the substrate heavily and drain it before using since the dust will otherwise collect at the bottom of the pot, sometimes random areas too, and impede drainage and root growth. For some reason kanuma and akadama are often mixed in equal portions, the advantage over using one form pure is not really specified. I agree with Michael Smith that kanuma is the better product and works very well straight, or in large pots with perlite added (normal size, not large). Akadama seems to break down faster into a muddy substrate while kanuma holds up as long as it is not crushed etc, however this arguably varies by batch.
Peat is an interesting substrate. It would appear that it was once much more widely used for Nepenthes but has lost favor to Sphagnum. In Germany, there are still growers that use it proficiently, and it is not relegated to lowland species as one might expect but instead N. lowii and the like is grown in it with spectacular results compared to the majority of US collections. While many growers would point out that it is not airy enough and is too wet for use with Nepenthes, this is not strictly true but points to the bigger issue which simply put is the sheer variability of peat batches. It must be understood that the peat sold in hardware stores across the US is the lowest quality grade peat and is used for little else than selling to homeowners planting flower beds and the like. Growing grade peat is sold specifically for nurseries in several different grades by various wholesale suppliers and is a much different product, being less wet and sticky with the best grades being brown in color (not black) and fluffy even without perlite. As the US peat supply comes almost exclusively from Canada while Europe’s supply grows in various countries there it is not too surprising as Xavier explained that the nutrient compositions of these peats are different due to their different environments of origin, with the highest grade (and apparently difficult to obtain) peat being EU only. I’m not sure just how big of a difference there is between these two sources, but it seems like at least the higher grade growers peat in the US is usable for Nepenthes if PH is adjusted appropriately and perhaps is superior to coir since it would appear to have less phytotoxic compounds and more normal nutrient concentrations. This would of course need to be confirmed with soil tests but seems likely the case. Ideally the peat would be used with polyurethane foam cubes since perlite actually doesn’t increase airiness that much (rather it lightens the pot and breaks up the media) but it seems the horticultural product is impossible to get in the US.
Rockwool is the last media of any note, but I already made a blog post on it. For most growers, coir and kanuma will achieve very good results.
Light & Temperatures
Generally, intermediate temperatures can achieve good growth for all the species with a day temp in the high 70s and nights in the 60s. The temp drop is less about hitting a certain temp, but rather is making the nightly photosynthesis process easier on the plant. Lowland plants would prefer it warmer, but a lot of the issues can be fixed via fertilizers. Similarly, the dying back of vines during hot spells in highland species is also a nutrient issue that is related to the macronutrients and specifically one micro.
Good bright light is recommended. Many LED brands do not produce a full spectrum as claimed since that is just the nature of LEDs… they produce specific wave lengths. No amount of false marketing will change that fact. However, many brands do achieve good growth. I use a mix of LEDs and original T5 fluorescents at 6500 K I believe, along with CMH which is only useful for very large enclosures. CMH is the closest light to natural sunlight and has the benefit of UV which some species genera require – many nightshades for instance produce Vitamin D which requires UV for synthesis. “Sunburning” is always related with nutrient deficiencies because the plant is trying to shade out the light (blushing red) and reduce the internal demands for more nutrients to keep pace with the light supply, which is why a reduction of light often improves matters but never resolves it fully. Many neps in the wild grow in full sun, after all, vines vine to reach the light, not stay in the shade.
Diseases & Pests
Nepenthes have very few diseases in fact. Almost always nutrient deficiencies are mislabeled as a fungal issue etc with no idea of what is actually going on. Fungal issues are distinct, they typically cause round leaf spots or sunken dead lesions.
The only important fungal issue for growers to concern themselves with is Pythium and Phytophthora, which in fact are oomycetes not fungus. This pathogens are primarily responsible for root and stem rot and act very quickly (there is also root suffocation [typically from heavy peat with no new root growth] and true root burn but that is later). In truth, almost all plants are infected with these or it dwells in the substrate. Any stress on the plant can trigger a “flare,” that is repotting, long shipping, a severe deficiency, root suffocation, or uneven soil moistures. Currently, the main thought process on this disease is that it is a mystical punishment for you overwatering your Neps. This makes no logical sense because Nepenthes grow in rainforests…
Using Azoxystrobin as a preventive every couple months and when repotting can help with this issue although it has the weakest effect on stopping rot. It is however the most available fungicide that has an effect on these pathogens since it is sold by Scotts for lawns for a cheaper price.
A lot of growers have a diehard fascination with Eagle fungicide which has zero effects on stopping rots and since that is the only issue worth fixing, imo is completely a total waste of time and money. It is used to improve leaf damage from opportunistic fungus but this is accomplished more readily with fertilizers.
Another option to mix with another fungicide is Mancozeb/Dithane which is cheap and available. It again doesn’t work that great but helps, and also vastly improves the growth of some species like reinwartdia.
For those that have severe issues and wish to spend the money, Fosetyl-Al works very well unlike the other options but must be used with lime if watered in. Can be sprayed too.
For plants that already have rot then they must be cut and rooted. Generally, rot can be identified by growth stalling, the leaves wrinkling and wilting that does not improve with watering or bagging, and finally, the leaf bases turning black and spreading towards the tip – this symptom moves up the stem in an ascending fashion which indicates the progress of the rot (in fact the rot in the stem is typically farther up the stem than this external symptom).
Generally, always err on cutting the plant once it wilts and lack of water was not the cause if it does not improve after a day. To confirm, you can make a nick into the lower stem to see if the stem inside is brown. If not, then the plant can be buried at the nick and it will make more roots from the wound. However, stem rot does not always expand in a linear fashion up the stem and sometimes it is just a small spot in a random location that is difficult to detect, so the nicking test is not foolproof. More on rooting the cuttings below. It should be noted that a severe nutrient issue can compromise the plant’s defenses so badly that no amount of fungicides can save it. In the wild, plants are typically better fed and hence have less diseases – otherwise they would be extinct.
Bacteria issues are uncommon but cause a melting of the stem. Viral issues can also occur in Nepenthes but so far none have tested positive in my collection. Typically in Nepenthes and orchids alike, it is simply taken for granted that their collections are virus free with zero proof, thinking a virus would give visible symptoms – in fact typically the plant remains green and grows slowly.
Thrips scarring on new leaf.
The most common pests in Nepenthes are thrips, scale, fungus gnats and mites. Contrary to what is said, thrips are almost never ever seen since they live in the actual growth point out of sight and cause scarring of new leaves and stunting. Scale are typically found on the underside of the lower leaves by the midrib, resembling a small lump or bit of dirt. Scale are problematic since they inject toxins which slow the plant, typically they like hamata type species but even macrophylla will be attacked. Fungus gnat larvae eat the roots quite efficiently. Mites cause similar damage to thrips but give a leathery appearance to the leaves, again they are not visible.
Very few obtainable non-banned pesticides work well on thrips and hard scale. Only Dinotefuran and I believe Orthene works on hard scale, and both work on thrips. Either work very well at eliminating fungus gnats. However, Orthene smells so terrible that it can only be recommended for outdoor greenhouses. Typically, the thrips will eventually rebound after some months since they gain resistance easily. Never use Imidacloprid (Bayer) due to mite flaring – the mites will become completely pesticide resistant and impossible to eradicate, this is a known fact that a google search will reveal. Also, Imidacloprid works dismally on thrips. Again, just because something is widely recommended doesn’t mean it works, its actually because it is cheap.
Spinosad can also work very well on thrips but is chemically between the neonicotinoids (Dinotefuran) and abamectine (Avid) which is our best defense against mites, so the risk of resistance seems higher in my mind. However, it does work as a spray and must be watered into the substrate at the same time too.
Avid works on both mites and thrips. Has to be sprayed twice about 2 weeks apart if I recall.
Forbid also works on the typical mites that plague Nepenthes but is expensive. Some growers buy predatory mites but who knows how long that investment lives, and they definitely don’t live once an actual miticide has to be used. Since Nepenthes are expensive, predatory mites seems like too casual a method of fixing a real issue. If neither avid or forbid works on the mites, then the symptoms should be checked again for thrips.
Cuttings
Cut the plant back to the green stem with a sterile knife and root it in new media. Cutting under water is a wonderful myth since the cut scars over regardless within a day even when rooted in water, so in effect the only purpose of cutting underwater is to allow easier access for fungus penetration. Cuttings in fact absorb all their moisture from the sides of the stem not the cut itself which makes sense due to where the new roots emerge from. So best is to just make a clean cut.
Cuttings typically root faster in kanuma or coir than sphagnum. Higher levels of humidity is often beneficial especially with Sumatran species which have lower rooting success.
Random Issues
There is the issue of basals outgrowing the main vine that many experience and believe is normal – for me at constant fertilization, the basals and vine grow at the same rate and never stall.
Seedlings often bleach white and once that occurs many are lost to rot. Again, this is a fertilizer issue but unfortunately all the regular fertilizers will quickly worsen the issue due to again, N pushing the growth beyond the supply of other nutrients. The best option is preventative doses of the root fungicides previously mentioned (applied at time of sowing) and sowing on finely chopped sphagnum or high grade peat (a great rarity). Using lime can possibly help the issue too but is not the cause. While I do know the exact cause of the bleaching, it is not to my advantage to share it since very few would try it except for other nurseries. In the meantime, I can offer a fertilizer that does in fact cure the issue unlike maxsea, osmocote, fill-in-the-blank – as I have spent a lot of time, financial, and plant losses performing lab tests and experiments I must remind anyone who objects to the withholding of information that I am not obligated to offer it.
Seeds do seem to sprout quicker under dim lighting. There is occasionally an issue of seed molding but it seems so far that the mold only attacks nonviable or weak seeds since seeds with high germination rates rarely mold. If the mold is an issue, Captan can be suspended in the watering solution and sprayed onto the seeds. Captan is just a contact fungicide that works very well for such things and dipping cuttings but otherwise is not too useful. Never use Physan or the like that rely on a PH difference rather than a curative effect.
Improperly forming pitchers or defective tendrils so far is connected to one of the micronutrients for certain. It is also likely connected with Potassium which serves as an osmocotium (water/leaf turgor regulator) and thus responds with higher humidity which relieves the plant’s demands. The “fertilizer stops pitchering” story is inaccurate and rather a nutrient imbalance again. This is easily proved since both Wistuba and BE fertilize pretty much constantly, and in fact is true for almost all the larger growers, while they meanwhile tell the little grower to use “pure water.” Again, just cause somebody did fertilization badly does not make blanket statements true.
Occasionally, there are plants that start turning many different colors suddenly with no improvements. Reds, lots of yellow, a crispy edge on random leaves with not much rhyme or reason and sometimes red dots – typically this occurs in old media especially sphagnum. This is caused by a PH issue from when the media breaks down and likely releases some weird substances. PH issues are also the cause of root burns from fertilizer, not the fertilizer itself. The concept is simple, the PH drops when fertilized down to PH 3 if not controlled and the roots die from the acidity. Control the PH and the plants can tolerate a very high EC (PPM). Whether they grow fast at that high ppm depends entirely on the fertilizer and managing of deficiencies.
Fertilizers
Leaving off the last concept, PH is critical to fertilizing. Nepenthes prefer the 5.5-5.8 range. Substrate choice plays a part in PH with Sphagnum being more acidic, coir and kanuma being less so. The biggest producer of the acids however is the plant itself, they can change soil PH within a day and that is a certain fact. The PH they change it too depends on soil buffering and the fertilizer itself, with generally nitrate raising the PH and ammonium lowering it. Urea raises the PH temporarily then lowers gradually, however for Nepenthes urea, while a very good nitrogen source, is not as easy to use.
Like Paphs, Nepenthes prefer ammonium/urea, not nitrate. Sadly, there is a very bad myth that circulated in orchids thanks to very bad misinterpretations of faulty data and a mistaken believe that orchids are vegetables, that myth being that orchids need nitrate nitrogen. While they do use nitrate, it is not preferred and can be toxic if not managed properly. For the sake of PH control (since many growers cannot be expected to buffer the PH with carbonates) nitrates can be used as an effective fertilizer as long as a portion of nitrogen is ammonium. Wistuba’s fertilizer is 50/50 ammonium to nitrate, and BE uses a mix of both as well, although I believe more heavy on the nitrate. EP’s fertilizer “ESF” fertilizer is a slow release pellet produced by Bailey’s AU that is likely a mix as well.
For clarity, do not use MSU fertilizers. They are all nitrate, specifically they contain a large chunk of Calcium nitrate which is very toxic to Nepenthes if given in any quantity unlike Potassium nitrate or Ammonium nitrate. Calcium toxicity results in an instant stalling of growth for months. Other forms of Calcium (hard water, lime) so far are absolutely safe because there is no nitrate to force absorption. MSU had (limited) success in orchids due to the university’s backing of a different product than typically sold (they used the well water special not rainwater mix and neither were based on any so called “tests”), the raising of the soil’s PH due to nitrate which relieves some plant stress, the higher levels of Magnesium that greens up the leaves, and finally, false advertising by nurseries selling MSU fertilizers and claiming they use them themselves. For sure MSU fertilizers is responsible for killing more orchids than any other fertilizer. But before getting sidetracked…
As a general recommendation, a low nitrogen dry soluble fertilizer should be used via the soil, or for those concerned, via the pitchers although less efficient. Foliar fertilizing for regular growing is pretty much useless unless you need to kill some time. Never use premixed liquid fertilizers since the nutrient composition is different than advertised and also they are buffered very acidically. It is not hard to dissolve a powder fertilizer. By low nitrogen, I do not mean keeping a low ppm of N since Nepenthes can use a lot, but rather PK should be higher. A balanced 20-20-20 fertilizer can work in a pinch but can worsen “sunburning” if used consistently. To prevent PH issues which cause “fert burn,” hardwater can be mixed in with the RO water as long as chlorine free or dolomite lime can be added to the pot surface (powdered not the pelleted) – either option gives very low odds of the PH going too high so that is not a concern. Northiana, campanulata, mapu, etc all grow on limestone…
As a general recommendation, Jacks 10-30-20 bloom booster should give good results with all the Nepenthes although will not work as well as a custom fertilizer.
Slow release pellets should be used in soil around 12 pellets minimum per 3.5" pot (same rate as BE) - via pitchers will only result in the pitcher die off. There is a couple of generic osmocotes, a complete with micronutrients should always be used. Nutricote has some more options and a steadier release.
Magnesium sulfate should be used on a regular basis, it is almost a universal deficiency in Nepenthes. Use at around ¼ tsp per gallon consistently, rates can be adjusted per conditions. Typically, Mg effects the old growth, less so the new leaves but is important for the leaves living a long time. It is unnatural for leaves to die off early.
Mild Magnesium deficiency in lower leaf.
Potassium deficiency crisp often found in veitchii, truncata, and flowering Neps - it is not chemical burn, too much light, fungus, or any other unproven fantasy. Vegetable symptoms in squash etc are quite similar.