Nepenthes in inorganic media?

Peat is ubiquitous in horticulture. A lot of gardeners turn to peat moss as an amendment to loosen up clumpy soil. Those who grow carnivorous plants often use the "standard CP mix," which is 1:1 peat and perlite, for many species. For Nepenthes, most mixes involve long-fiber sphagnum moss. LFS is popular for orchids, too. It retains moisture, allows air to get to the roots, and even has antibacterial properties. What's not to love? 

Well, for starters, sphagnum breaks down over time. The wetter the mix, the more frequently the plant will need to be repotted. Fortunately, sphagnum is readily available in most garden centers and online.

Unfortunately, sphagnum is not sustainable (see here and here). For most plants, there are a lot of more sustainable alternatives, including compost and coconut coir or coco "peat" (a byproduct of the coconut industry). Compost is out for Nepenthes, which are sensitive to nutrients in the soil and prefer an airier mix anyway. Coconut products are a better alternative. The only drawback is that they are often saturated with salts and need to be soaked and washed in pure or distilled water several times first.

I want to wean myself off sphagnum, but rinsing coconut products in pure water isn't really feasible for someone who buys his distilled water from the store. So, I'm experimenting with inorganic mixes.

There are as many soil mixes for Nepenthes as there are growers. Some will swear that there is no alternative to sphagnum, others will tell you they successfully grow their plants in floral foam. There is, of course, no perfect mix and other factors (temperature, humidity, fertilization, frequency of watering, etc.) need to be accounted for when choosing a mix.

I already grow my Nepenthes vieillardii in a mostly inorganic mix, composed of turface, perlite, laterite, lava rock, hydroton, and fine-grade orchid bark.

N. vieillardii

N. vieillardii is one that often limps along in collections, growing but never quite thriving. One grower has had success growing it in a drier, grittier mix, given that the plant grows naturally in the dry, lateritic soils of New Caledonia. After a few months growing it in long-fiber sphagnum, I decided to give the aforementioned mix a shot. Time will tell.

What about the rest of the genus? Nepenthes prefer acidic, moist, airy, nutrient-poor substrates and sphagnum fits the bill. After a lot of searching, I came across a soil called kanuma that is used for bonsai azalea and other calcifuges because it is reported to be more acidic than akadama, the usual bonsai substrate (though this is controversial).  Kanuma is a yellowish, lightweight, slightly crumbly soil from the Kanuma area in central Japan. It has great moisture retention yet allows plenty of air to get to the roots. Also, because it's soft, thin-rooted plants should have no trouble growing through it. This, I thought, might be an ideal base for an inorganic mix. Here are two N. ventricosa potted up in kanuma mixes:

  
The one to the left is in a mix of kanuma, perlite, and lava rock. The other is in a 50:50 mix of kanuma and perlite They haven't been in the mix very long, just a few days, but already I'm learning that it isn't easy determining how often to water. Since there is no organic material, fertilization will be necessary, too. I don't know how much, but certainly more than my other Nepenthes get. Only time will tell if this mix is suitable or not. But I do hope that this will bring me closer to a peat/sphagnum-free Nepenthes mix.