I purchased a Drosophyllum in a peat pot a few weeks ago and I plan to transplant it into a two feet diameter terra-cotta pot in the next few days. I just have a few questions before I put the plant into its permanent home.
The previous inhabitant of the pot was a cactus (Hylocereus to be specific) and after several years of growing about half of the pot was just the roots of the plant. The pot was put on concrete so the roots were unable to grow out from the pot. I am considering putting the pot on a patch of dirt so that the Drosophyllum's roots will be able to grow into the ground if they like. However, in Barry Rice's Growing Carnivorous Plants, he writes that Drosophyllum roots only grow ten to fifteen inches into the soil even in the wild. So should I just go ahead and put the pot on concrete? Or would the plant grow more if the roots have more room to spread?
Also, the growing medium I plan to use is about one part peat, one part perlite, one part 20 grit silica sand, and one part vermiculite. Does that sound right, or will the vermiculite hold too much water like the peat will? I've never used it as a growing medium before, so I'm not sure about it. Also, is 20 grit sand coarse enough? I couldn't find any coarser sand in local nurseries, and it is industrial sand, which I have never used before.
Finally, I've been growing the Drosophyllum in the front of my house where it receives six or seven hours of full sun each day in southern California. It has caught many insects, and yet the leaves it is making are becoming shorter than the leaves it had when I first purchased it. Is this due to stress or the new growing conditions, or is this some other problem? I was told by the nursery that the plant gets more compact in full sun, but I hope the plant doesn't remain small when I transplant it into a much larger pot.
Apologies for all the questions; I don't have any experience with this plant or with many of the substrates in which it is grown.
A picture of the plant soon after I got it:
I can only recommend the following:
1) This may not be an issue with your native CA soil, but here in the south our soil is loaded with pathogens, both fungal and bacterial. If I had a Drosophyllum that big I'd certainly place it on a bench or concrete or a plant stand. Plus, if Drosophyllum does end up rooting into the ground and you need to move it, you'll break the roots. Not only will that shock the plant, but it'll be left with a bunch of wounds that can allow the entry of soil pathogens.
2) Vermiculite doesn't last very long and is very prone to breakdown, whereupon it forms a disgusting wet sludge. I am currently growing baby Drosophyllum in a medium I use frequently (Turface, or Schultz Aquatic Plant Soil) and they seem to love it. I'm a huge fan of Turface because it resists compaction and breakdown forever. It provides constant air space. And because it is clay, it holds water and fertilizer at just the right amount. I would replace vermiculite with this if you're able to find it. If not, maybe add additional sand instead. I have grown hundreds of species of cacti, succulents, mesembs, etc. in a Turface/potting soil blend and it has lasted for years without me ever having to repot. It's insane how well it performs. If you feel drainage may be an issue maybe try looking into very small pieces of gravel (such as aquarium gravel).