Question
I have a 55 gal. Terrarium with various Nepenthes, pings and sundews.  All plants are doing well with the exception of one Nepenthes. It's leaves have lightened up to almost a greenish yellow and black spots are appearing. The plant is approximately 4 years old. Worried it is a fungus and transferable.
Currently at 10 hours of light per day. Humidity 50 to 70% and temps from 60 to 80. Humidity and temps fluctuate with lighting. I also have a fan blowing at all times. Soil is sphagnum moss on top and clay balls underneath for drainage.
Any suggestions?

Thank you.
Regards.
Dean

Answer
Hello Dean,

Terrariums are one of the main ways that many carnivorous plants die by. The variety of species you have all require different soil, different lighting, and different watering techniques to keep healthy and most of them probably do not require high humidity.

Terrariums induce mold, keep the plants from capturing household insect pests, hold in water and create bacterial breeding grounds near plant roots, hold in too much humidity and restrict air flow, restrict lighting systems, and simply are not conducive to ease of growing most plants of any kind.

Your best bet at this point would be to determine what species you have, which absolutely have to have high humidity to survive, and which can be grown open pot. Most Drosera do best in a mix of half sphagnum peat and half perlite with a tray watering system so that about 1/4 the bottom of the pot is in water. Most Pinguiculas are not so picky about soil, but need a large amount of drainage and less water than sundews in general. Keep Pinguiculas in pots with 1/3 or 1/4 sphagnum peat and the rest even mixture of perlite and vermiculite for drainage and some mineral content. Pings like some minerals in their soil. Nepenthes actually do best in airy mixes of 1/3 sphagnum peat, 1/3 orchid bark, and 1/3 perlite or coconut husk (not coco peat, but actual broken pieces of coconut shell). Nepenthes need a lot of drainage mixed in their soil like Pinguiculas and need less water than Sundews. Do not keep trays of water under Npenthes or Pinguiculas, merely have a tray to catch runoff water and let it dry out for a couple days between waterings. Only allow a fraction of an inch in the tray after watering.

Your Nepenthes might be suffering from a number of problems. If it is mold, you can remove some with a paper towel. If the mold is on particular spots, it might be simply mold growing on areas of nectar production on the leaves and pitchers, which occurs in Nepenthes when they get too little light and restricted air flow. That kind of mold is usually not a problem since it is eating the nectar, not the plant. If the black spots do not come off when wiped with a moist paper towel, then it might be leaf damage from too little light or too much water. Nepenthes need more light than Pinguiculas and as they grow larger, simply need more light over a larger area. Try increasing the light to 12 hours a day in Winter and to 16 in Summer. Make sure they are getting at least 12000 lumens of light intensity or more from cool white florescent lights over several feet of area to cover the leaf growth patterns. Nepenthes roots can suffer root rot when allowed to sit in stagnant water, which basically is what is in the bottom of an enclosed terrarium in the drainage layer. Nepenthes roots can grow out to find that layer, then may become infected and asphyxiated with bacteria laden stagnant water and begin rotting out, resulting in blackening leaves and a dying plant.

If you decide to remove the plants from the terrarium (make sure the plants are all capable of adapting to low humidity by first checking their species and humidity requirements), you will need to adapt them slowly to lower humidity over several weeks by opeing the terrarium slightly and keeping it open for two or three days. Only keep it open about a quarter or half an inch the first few days, then open it up another quarter inch every three days until about three or so weeks have passed. By that time, the top should be open a few inches and can be removed. Lower humidity will have inundated the terrarium slowly and the plants will have had time to adapt to it. Those that require high humidity can remain in the terrarium and can be protected with plastic bags while you adapt the other plants. Once adapted, the low humidity capable species can be repotted in regular pots and placed under florescent lights on a shelf as I keep all of mine.

If the Nepenthes with the leaf spots is suffering from too much water or too little light, the increase in light and decrease in stagnant water near its roots should help out. If it is mold, the increase in light and decrease in humidity should help out. Since the leaves are yellowing, it could be from low light or too much water. Both are inadequate at this time so change both for the better.

Christopher